Isabella Børja

Research Professor

(+47) 974 80 317
isabella.borja@nibio.no

Place
Ås H8

Visiting address
Høgskoleveien 8, 1433 Ås

Abstract

In Norway the common ash (Fraxinus excelsior L.) has its northernmost distribution in Europe. It grows along the coastal range as small fragmented populations. The first occurrence of ash dieback caused by Hymenoscyphus fraxineus in Norway was reported in 2008. At that time, the disease had already spread through large areas of southern and south-eastern parts of Norway. Since then the disease continued spreading with a speed of about 50- 60 km per year along the western coastal range. To monitor the disease development over time, we established eight permanent monitoring plots in south-eastern and western Norway in 2009 and 2012, respectively. In all plots tree mortality was high, especially among the youngest trees in south-eastern Norway. The extent of crown damage has continually increased in all diameter classes for both regions. In 2009, 76.8 % of all trees on the five monitoring plots in south-eastern Norway were considered to be healthy or slightly damaged, and only 8.9 % to be severely damaged. In 2015, 51.7 % were dead, 13.5 % severely damaged and only 25.7 % remained healthy or slightly damaged. To assess the infection pressure and spore dispersal patterns of the pathogen, we used a Burkard volumetric spore sampler placed in an infested ash stand in southern Norway. We examined the airborne ascospores of H. fraxineus and H. albidus captured on the sampling tape microscopically and with real-time PCR assays specific to these fungi. We detected very few ascospores of H. albidus, whereas ascospores of H. fraxineus dominated throughout entire sampling periods of 2009, 2010 and 2011. Spore discharge occurred mainly between the hours of 5 and 8 a.m., though the distinctive sporulation had yearly variation between 5-7 a.m. We observed the same diurnal pattern throughout the entire sampling period, with a seasonal peak in spore liberation between mid-July and midAugust, after which the number of ascospores decreased substantially. Similar diurnal patterns were observed throughout the sampling period except that after mid-August the number of trapped ascospores substantially decreased. To compare the genetic pattern of common ash in the northern and central ranges of Europe we analyzed the Norwegian samples together with available samples from central Europe by using chloroplast and nuclear microsatellite markers. We found that the northern range of common ash was colonized via a single migration route that originated in eastern or south-eastern Europe with little influence originating from other southern or western European refugia. In the northern range margins, genetic diversity decreased and population differentiation increased, coherent with a post-glacial colonization history characterized by founder events and population fluctuations. Based on our findings we discuss the future management and conservational implications.

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Abstract

High biodiversity is regarded as a barrier against biological invasions. We hypothesized that the invasion success of the pathogenic ascomycete Hymenoscyphus fraxineus threatening common ash in Europe relates to differences in dispersal and colonization success between the invader and the diverse native competitors. Ash leaf mycobiome was monitored by high-throughput sequencing of the fungal internal transcribed spacer region (ITS) and quantitative PCR profiling of H. fraxineus DNA. Initiation of ascospore production by H. fraxineus after overwintering was followed by pathogen accumulation in asymptomatic leaves. The induction of necrotic leaf lesions coincided with escalation of H. fraxineus DNA levels and changes in proportion of biotrophs, followed by an increase of ubiquitous endophytes with pathogenic potential. H. fraxineus uses high propagule pressure to establish in leaves as quiescent thalli that switch to pathogenic mode once these thalli reach a certain threshold – the massive feedback from the saprophytic phase enables this fungus to challenge host defenses and the resident competitors in mid-season when their density in host tissues is still low. Despite the general correspondence between the ITS-1 and ITS-2 datasets, marker biases were observed, which suggests that multiple barcodes provide better overall representation of mycobiomes.

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Abstract

The ongoing climate change may have a distinct effect on Norway spruce growth, one of the most important tree species in European forest management. Therefore, the understanding and assessment of climate-growth relationship can help to reveal relevant patterns in temporal variability that may result in lower tree vitality and decline. The main objective of our study was to evaluate the long-term climate-growth variability of Norway spruce in south-eastern Norway, at the northern edge of the temperate zone. We sampled in total 270 dominant and co-dominant trees from 18 plots in south-eastern Norway. We analysed stem cores and evaluated crown condition parameters to assess the retrospective tree growth and vitality. Despite considerable differences in the crown parameters, high similarity among tree-ring width (TRW) series allowed compiling the regional tree-ring width chronology. Correlations between TRW and climate parameters showed temporal instability in their relationship during the period 1915–2012. While we did not detect any significant relationships between TRW and climate parameters in the first half of the study period (1915–1963), a significant correlation between TRW and spring precipitation was observed for the period 1964–2012. This shift appeared concurrent with temperatures reaching above-average values compared to the average of the climate normal period 1961–1990.

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Abstract

Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responses of fine roots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fine roots and fungal hyphae at different soil depths. In control plots fine roots proliferated in upper soil layers, whereas in drought plots there was no fine root growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphae followed the same pattern as fine roots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fine roots and fungal hyphae respond to long-term drought stress by growing into deeper soil layers.

Abstract

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, has been spreading throughout Europe since the early 1990s, threatening European ash at a continental scale. Little is known about the development of the disease in individual forest trees and in different age classes. In this study we monitored ash dieback on trees of different diameter classes in five permanent plots in ash stands in south-eastern Norway from 2009 to 2016, and from 2012 to 2016 in three plots in western Norway with a shorter disease history. Our results showed that more than 80% of the youngest and more than 40% of the intermediate future crop trees in the plots in south-eastern Norway were dead by 2016, while the disease development in large, dominant trees was slower. Although less damage has been observed in the plots in western Norway, the trend for the juvenile trees is the same as in south-eastern Norway with rapidly increasing damage and mortality. Most dead trees in south-eastern Norway were found at sites with high soil moisture and showed symptoms of root-rot caused by Armillaria species. Infected trees, both young and old ones, are weakened by the disease and appear to be more susceptible to other, secondary pathogens, especially under unfavourable site conditions.

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Abstract

There is evidence that recently occurring top dieback of Norway spruce (Picea abies (L.) Karsten) tress in southern Norway is associated with drought stress. We compared functional wood traits of 20 healthy looking trees and 20 trees with visual signs of top dieback. SilviScan technology was applied to measure cell dimensions (lumen and cell wall thickness) in a selected set of trunk wood specimens where vulnerability to cavitation (P50) data were available. The wall/lumen ratio ((t/b)²) was a quite good proxy for P50. Cell dimensions were measured on wood cores of all 40 trees; theoretical vulnerability of single annual rings could be thus estimated. Declining trees tended to have lower (t/b)² before and during a period of water deficit (difference between precipitation and potential evapotranspiration) that lasted from 2004 to 2006. The results are discussed with respect to genetic predisposition.

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Abstract

Top dieback in 40–60 years old forest stands of Norway spruce [Picea abies (L.) Karst.] in southern Norway is supposed to be associated with climatic extremes. Our intention was to learn more about the processes related to top dieback and in particular about the plasticity of possible predisposing factors. We aimed at (i) developing proxies for P50 based on anatomical data assessed by SilviScan technology and (ii) testing these proxies for their plasticity regarding climate, in order to (iii) analyze annual variations of hydraulic proxies of healthy looking trees and trees with top dieback upon their impact on tree survival. At two sites we selected 10 tree pairs, i.e., one healthy looking tree and one tree with visual signs of dieback such as dry tops, needle shortening and needle yellowing (n = 40 trees). Vulnerability to cavitation (P50) of the main trunk was assessed in a selected sample set (n = 19) and we thereafter applied SilviScan technology to measure cell dimensions (lumen (b) and cell wall thickness (t)) in these specimen and in all 40 trees in tree rings formed between 1990 and 2010. In a first analysis step, we searched for anatomical proxies for P50. The set of potential proxies included hydraulic lumen diameters and wall reinforcement parameters based on mean, radial, and tangential tracheid diameters. The conduit wall reinforcement based on tangential hydraulic lumen diameters ((t/bht)2) was the best estimate for P50. It was thus possible to relate climatic extremes to the potential vulnerability of single annual rings. Trees with top dieback had significantly lower (t/bht)2 and wider tangential (hydraulic) lumen diameters some years before a period of water deficit (2005–2006). Radial (hydraulic) lumen diameters showed however no significant differences between both tree groups. (t/bht)2 was influenced by annual climate variability; strongest correlations were found with precipitation in September of the previous growing season: high precipitation in previous September resulted in more vulnerable annual rings in the next season. The results are discussed with respect to an “opportunistic behavior” and genetic predisposition to drought sensitivity.

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Abstract

Top dieback of Norway spruce (Picea abies), triggered by drought in 2004–2006, has been observed in Southeast Norway and trees died within four years after appearance of the first symptoms. The aim of our study was to use sap flux measurements as a diagnostic method for assessment of tree vitality. We used the heat field deformation method to monitor the sap flux density (SFD) in four pairs of healthy and declining trees in situ. To provide retrospective information on hydraulic performance of the trees we took samples for wood anatomical analysis. After felling the trees we used the modified differential translucence method (MDT) as a proxy for the SFD measurements. Healthy trees had three times higher SFD values as declining trees. In some healthy trees we detected decreasing SFD with time. The MDT method agreed with the SFD measurements. In conclusion, we detected sap flux dysfunction in declining trees and showed that the SFD reduction may occur during a short period, prior to occurrence of any visual symptoms. We suggest incorporating the SFD measurements into the repertoire of diagnostic tools in forest pathology.

Abstract

Pythium species are fungal-like organisms distributed all over the world. Most Pythium spp. live as saprophytes, but some of them are pathogenic. Here we report on disease incidence in Norway spruce (Picea abies) seedlings caused by Pythium undulatum, and pathogenicity in vitro of Norwegian isolates of P. undulatum and P. anandrum.

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Abstract

Trees must respond to many environmental factors during their development, and light is one of the main stimuli regulating tree growth. Thinning of forest stands by selective tree removal is a common tool in forest management that increases light intensity. However, morphological and anatomical adaptations of individual shoots to the new environmental conditions created by thinning are still poorly understood. In this study, we evaluated shoot morphology (shoot length, needle number, projected leaf area) and anatomy (tracheid lumen area, tracheid number, tracheid dimensions, xylem area, potential hydraulic conductivity) in three Norway spruce (Picea abies/L./Karst.) families exposed to different thinning regimes. We compared shoot characteristics of upper-canopy (i.e. sun-exposed) and lower-canopy (i.e. shaded) current-year shoots in a control plot and a plot thinned to 50 % stand density the previous year. One tree per family was chosen in each treatment, and five shoots were taken per canopy position. We found that upper-canopy shoots in both plots had higher values than lower-canopy shoots for all studied parameters, except lumen roundness and tracheid frequency (i.e. tracheid number per xylem area). Thinning had little effect on shoot morphology and anatomy 1 year after thinning, except for small but significant changes in tracheid dimensions. Needles were more sensitive to altered light conditions, as projected leaf area of shoot, needle number and leaf hydraulic conductivity changed after thinning. Differences between upper- and lower-canopy shoots did not seem to be influenced by thinning and were almost the same in both plots. Our results suggest that lower-canopy shoots require several years to modify their morphology and anatomy to new light conditions following thinning. The slow light adaptation of the lower canopy may be of practical importance in forest management: thinned stands may be predisposed to drought stress because newly exposed shoots experience increased illumination and transpiration after thinning.

Abstract

Ari M. Hietala, Volkmar Timmermann, Isabella Børja & Halvor Solheim Norwegian Forest and Landscape Institute. PO Box 115, 1431 Ås, Norway: ari.hietala@skogoglandskap.no Owing to the Gulf Stream, the northernmost European populations of several tree species are found in Norway. Common ash (Fraxinus excelsior), the only native ash species in Norway, is present in the lowlands in the southeastern part with continental climate and in southern and southwestern coastal regions with North Atlantic climate up to Central Norway. The current standing volume of ash in Norway is ca 3 mill m3 (broadleaved trees in total 220 mill m3). The first documentation of Ash Dieback (ADB) is from 2008 from a nursery in the southeastern part of the country. A survey later that year showed that dieback symptoms were present over a distance of nearly 400 km in the southeastern region. In addition to nurseries and forests, ADB symptoms were observed on roadside, alley, garden and park trees. Based on the presence of old ADB-like stem lesions detected in 2008, the pathogen must have arrived to Norway no later than 2006. In 2008, the Norwegian Food Safety Authority laid down regulations with the aim of preventing further spread of ADB. These regulations divide the country into quarantine, observation and infection-free zones, and prohibit the export of ash seedlings, seed and wood from the quarantine zone. Despite of these regulations, the disease spread rapidly along the western coast in the period between 2009 and 2013, and currently only the ash stands in Central Norway are free of the disease. The rapid spread of the disease in Norway is obviously due to airborne dispersal of pathogen ascospores. In our experimental stand in SE Norway the number of pathogen fruit bodies can be as high as 10,000 per m2 in the peak season, mid-July to mid-August. During the early morning hours the amount of pathogen ascospores at a diseased stand can exceed 100,000 ascospores per m3 air. The first symptoms of the disease, necrotic lesions on leaf blade and petiole, appear typically during the first two weeks of August in SE Norway. To observe long-term impacts of ADB, eight monitoring plots have been established in continental and North Atlantic climate zones. In SE Norway with the oldest disease history, above 60 % of the trees with a breast height diameter (BHD) below 12.5 cm have so far died or suffer from severe defoliation, 1/3 of the larger trees being affected to a similar degree. The proportions of healthy (no signs of defoliation) small and larger trees are 20% and 37%, respectively. In SW Norway with more recent disease history a similar trend is observed but the proportion of dead trees is still small. As a consequence of ADB, the Norwegian nurseries no longer grow ash seedlings. There are currently no practical control options for the disease in forestland. Several European countries have reported that even at heavily diseased ash stands there are often some ash trees that show little symptoms. This may be due to genetic variation between trees in disease resistance, a hypothesis that is currently being investigated in several European projects. Thus implementation of forest management practices that eliminate ash could have a negative effect as survival of the tree ultimately depends on selection of trees with increased disease resistance. Bibliography for Ari M. Hietala Ari M. Hietala is a Senior Forest Pathologist at the Norwegian Forest and Landscape Institute, which is a primarily government funded organisation providing scientific research and services to government, non-governmental and commercial organisations. He has worked with a range of fungal root and shoot diseases occurring on broadleaved trees and conifers indigenous to the Nordic countries. Ari and the rest of the group participate currently in several European consortia engaged in ash dieback research.

Abstract

In cases where sap flow is measured in trees and cross-sectional sapwood is not uniformly distributed, as in stems of diseased trees, an additional method may refine the sap flow measurements. If the studied trees are felled, the modified differential translucence method (MDT) for quantifying sapwood distribution in cross-sectional area may be compared with sap flow measurements. We studied sap flow by the heat field deformation method (HFD) in 12 Norway spruce trees with visible dieback symptoms and 12 without symptoms. Later, all sample trees were felled and analysed by MDT method. Results from MDT described well the differences and abnormalities which were also detected by HFD at any depth of the sapwood. Sap flow for whole tree (SF1) was calculated in accordance with radial and circumferential variation of sap flow density detected by HFD (based on average sap flow radial profiles). Other sapwood disturbances in parts not covered by HFD measurements were later corrected by MDT and refined total sap flow (SF2) was calculated. Relative differences between SF1and SF2 reached an interval from -0.21 to 0.41 for symptomatic trees and from -0.15 to 0.29 for non-symptomatic trees. The majority of the non-symptomatic trees had the relative difference close to zero. The theoretical use of single-point sensors for sap flow measurement was compared with the proportions of three wood types in a line 2 cm below the vascular cambium (a-sapwood, b-borders sapwood/heartwood or embolism, c-heartwood or embolism). The variability across wood types in the chosen line in the symptomatic trees was high and therefore quantifying the sap flow by the single point method was not possible.

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Abstract

Purpose: Drought-induced tree susceptibility is a major risk associated with climate change. Here we report how an 11-week drought affected tracheid structure, gene expression, and above- and belowground growth in 5-year-old Norway spruce trees (Picea abies) under controlled conditions. Results: The canopy of trees subjected to severe drought had significantly less current-year needle biomass, and fewer tracheids and tracheid rows in current-year shoots compared to fully watered control trees. Belowground tissues were more strongly affected by drought than aboveground tissues. In fine roots (<2 mm diameter) severe drought significantly reduced root biomass, root diameter, root length density and root surface area per soil volume compared to the control. Tracheid diameter and hydraulic conductivity in fine roots were significantly lower and tracheid flatness higher in trees subjected to severe drought than in control trees, both for long and short roots. Transcripts of the drought-related dehydrins PaDhn1 and PaDhn6 were strongly upregulated in stem bark and current-year needles in response to drought, whereas PaDhn4.5 was down-regulated. Conclusions: This study demonstrates that drought reduces biomass and hydraulic conductivity in fine roots and needles. We suggest that the ratio between PaDhn6 and PaDhn4.5 may be a sensitive marker of drought stress in Norway spruce.

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Abstract

Estimates of root absorption magnitude are needed for the balanced management of forest ecosystems, but no methods able to work on the whole tree and stand level were available. Modified earth impedance method was developed recently and here it was tested, by comparing the results with those obtained by combination of several classical methods. Methods We used direct (soil cores, scanning and microscopy) and indirect (sap flow patterns and modified earth impedance) methods in an attempt to estimate the absorptive root area indexes (RAI) at two sites of about 25 and 40-years-old Norway spruce. We considered the geometric surfaces of all scanned fine roots to be equal to the fine root absorptive area (RAIscan). To estimate the potentially physically permeable area of fine roots, we microscopically evaluated the point of secondary xylem appearance and calculated the geometric area of root portions with primary structure (RAImicro). We termed the area of electrically conductive root surface as the active (ion) absorptive area (RAImei) and measured its extent by the modified earth impedance (MEI) method. Results The highest values for absorptive root areas at the two experimental sites we obtained with the scanning method (RAIscan was considered to be 100%), followed by the RAImicro (51%) and RAImei (32%). RAImei reached about 2/3 of RAImicro. The surface area of the ectomycorrhizal hyphae was an order of magnitude larger than that of all fine roots, but the MEI did not measure such increase. Conclusions We showed that the absorptive root area, indirectly estimated by the MEI, provides consistent results that approach the values obtained for fine roots with a primary structure estimated by traditional direct methods. The similar range of the values for the absorptive root surface area obtained by microscopy and by the MEI method indicates that this method is feasible and that it could be used to determine the extent of active absorptive root surface areas in forests.

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Abstract

Background and Aims: Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values. Methods: We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature. Results: Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0.86 yr−1 for Fagus sylvatica and 0.88 yr−1 for Picea abies when maximum biomass data were used for the calculation, and 1.11 yr−1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula. Conclusions: We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting.

Abstract

Top-dieback of Norway spruce (Picea abies) trees has been observed in SE Norway. Trees usually die within 1-4 years after the first symptoms become visible and the dieback cause is unknown. The aim of our study was to establish when the irreversible spiral to tree death occurs. We assumed that hydraulic dysfunction, exemplified here by the sap flow reduction, was the final trigger of tree decline. We used the non-destructive heat field deformation method (HFD) to monitor the sap flow density (SFD) in non-symptomatic trees. After felling the trees we used the modified differential translucence method (MDT) to evaluate the sapwood translucence as an additional indicator of its functionality. In this study we show three examples of non-symptomatic trees with widely different sap flow densities detected by the HFD; tree A with unchanged sap flow throughout the monitoring period, tree B with decreasing sap flow in the last formed annual rings and minimal sap flow detected in tree C, which also started to show the first visible signs of dieback. In contrast, the MDT method detected in all cases functional (translucent) sapwood. In conclusion, we show that the sap flow reduction may occur during a relatively short period, prior to occurrence of any visual symptoms. Also, dysfunctions in sap flow could not be detected by the MDT method, as the sapwood still looked translucent and thus functional, although minimal sap flow was detected in that area by HFD method. Here we demonstrate the sensitivity of the HFD method in detecting the quantity of sap flow and thus a suitable diagnostic tool to evaluate the vitality in Norway spruce trees before the onset of visible disease symptoms.

Abstract

Shoot dieback disease of European ash caused by the ascomycete Hymenoscyphus pseudoalbidus threatens ash on a continental scale. A spore sampler placed in a diseased ash forest in Southern Norway, coupled with microscopy and DNA-based fungal species-specific real-time PCR assays, was employed to profile diurnal and within-season variation in infection pressure by ascospores of H. pseudoalbidus and the potentially co-existing non-pathogenic Hymenoscyphusalbidus. Hymenoscyphus pseudoalbidus was found to be predominant in the stand. Massive simultaneous liberation, by active discharge of pathogen ascospores in the morning, peaked in mid-Jul. to mid-Aug. Accumulation of pathogen DNA on leaflets of current-year leaves reached a high level plateau phase before appearance of autumn coloration, suggesting that pathogen establishment in leaves is terminated before the onset of leaf senescence.

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Abstract

Conifer needles are extraordinarily variable and much of this diversity is linked to the water transport capacity of the xylem and to xylem conduit properties. However, we still know little about how anatomical characteristics influence the hydraulic efficiency of needle xylem in different parts of the crown. In this study we evaluated needle function and anatomy in Norway spruce families exposed to different light conditions. We measured tracheid and needle characteristics of sun-exposed and shaded current-year needles in two experimental plots: a control plot and a thinned plot with 50% reduction in stand density. Sun-exposed needles had a larger tracheid lumen area than shaded needles, and this was caused by a larger maximum tracheid lumen diameter, while the minimum lumen diameter was less plastic. Sun-exposed needles had also higher theoretical hydraulic conductivity than shaded needles. Thinning leads to increased radiation to the lower branches, and presumably exposes the upper branches to stronger water stress than before thinning. Thinning affected several needle parameters both in sun-exposed and shaded needles; tracheid lumens were more circular and minimum tracheid lumen diameter was larger in the thinned plot, whereas maximum tracheid lumen diameter was less plastic on both plots. This study demonstrates that needle xylem structure in Norway spruce is clearly influenced by the light gradient within the tree crown.

Abstract

In South-east Norway, several scattered observations of reduced growth and dieback symptoms were observed over the last 20 years in 40-60 years old Norway spruce (Picea abies) trees. Typical symptoms start with yellowing in the top and subsequent dieback downwards from the top. These symptoms are often combined with bark beetle (Ips typographus), honey fungus (Armillaria spp.) infections, and a sudden decrease in diameter and height growth. After about 1-5 years, most of the symptomatic trees are dead.We selected 11 representative stands in six counties. In each stand all trees in ten 250 m2 plots were evaluated, in total about 4000 trees. In each of these 110 plots, one symptomatic and one non-symptomatic tree were investigated in more detail. We measured tree diameter, height, took increment cores and assessed crown condition, wounds, resin flow, stem cracks, bark beetle infection and Armillaria presence. In addition, internode lengths of the last 20 years were measured in two of the stands.Preliminary results of internode lengths and increment cores showed a sudden decrease of height and diameter growth in the symptomatic trees. Many of these trees had a secondary infection of bark beetles and Armillaria. Some years appear to be typical problem years for many of the trees. These years also correspond with summer drought, i.e. negative Palmer drought severity indexes which were estimated for each stand. In comparison, the non-symptomatic trees, growing close to the symptomatic ones, showed none or minor growth reductions and discolouration.Climate change and increased summer drought may worsen spruce dieback problems. Management adaptions are uncertain. We conclude that Norway spruce is sensitive to drought, which reduce the growth and weaken the health, and probably reduce the defence against secondary infections.

Abstract

Dieback of European ash (Fraxinus excelsior), caused by the ascomycete Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea), started around 1992 in Poland and has since then spread over large geographical areas. By November 2010, the disease had been recorded in 22 European countries. The gradual expansion and high intensity of the ash dieback epidemic in Europe may suggest that H. pseudoalbidus is an invasive alien organism. In Norway, ash dieback was first reported in spring 2008, and a survey in early summer of the same year revealed that the disease had spread over large parts of the southern and eastern regions of the country. The distance from the southernmost to the northernmost infected stands was, at that time, about 400 km. Some old necrotic lesions were also observed, indicating that the ash dieback pathogen is likely to have been present in Norway since at least 2006. In 2009, a spore sampler was installed in a diseased ash stand at Ås, South-Eastern Norway. Sampling started in late July and continued until late September. Large numbers of ascospores resembling those of H. pseudoalbidus were observed, with the maximum number of spores occurring from the end of July to mid-August. The deposition of ascospores occurred mainly between 6 and 8 a.m. Ascospores are most likely to be the primary source initiating host infections and responsible for the rapid recent spread of H. pseudoalbidus in Europe.

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Abstract

Conifers and other trees are constantly adapting to changes in light conditions, water/nutrient supply and temperatures by physiological and morphological modifications of their foliage. However, the relationship between physiological processes and anatomical characteristics of foliage has been little explored in trees. In this study we evaluated needle structure and function in Norway spruce families exposed to different light conditions and transpiration regimes. We compared needle characteristics of sun-exposed and shaded current-year needles in a control plot and a thinned plot with 50% reduction in stand density. Whole-tree transpiration rates remained similar across plots, but increased transpiration of lower branches after thinning implies that sun-exposed needles in the thinned plot were subjected to higher water stress than sun-exposed needles in the control plot. In general, morphological and anatomical needle parameters increased with increasing tree height and light intensity. Needle width, needle cross-section area, needle stele area and needle flatness (the ratio of needle thickness to needle width) differed most between the upper and lower canopy. The parameters that were most sensitive to the altered needle water status of the upper canopy after thinning were needle thickness, needle flatness and percentage of stele area in needle area. These results show that studies comparing needle structure or function between tree species should consider not only tree height and light gradients, but also needle water status. Unaccounted for differences in needle water status may have contributed to the variable relationship between needle structure and irradiance that has been observed among conifers.

Abstract

Fungi are the main degraders of organic matter and are associated symbiotically with over 80% of terrestrial plants (Smith and Read 1997). Thus, the extent of the mycelial network is an indicator of the decomposing or symbiotic activity. Although the importance of fungi in soil is undisputable, the determination of the extent of hyphal mats and the hyphal biomass is difficult to assess. Methods for estimating hyphae in soil are mostly based on the gridline intersect method originally developed to determine the root length or recently by measuring of the ergosterol content, fungal sterol found in the cell membranes....

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Abstract

Molecular methods are emerging also as useful tools for wood protection studies. The aim of the present study was to evaluate quantitative real-time polymerase chain reaction (qPCR) as a tool for investigating details of the colonization pattern of basidiomycete decay fungi in wood samples after 6 years of soil exposure. Samples of Pinus sylvestris L. (heartwood without treatment), furfurylated P. sylvestris sapwood and Cu-HDO treated P. sylvestris sapwood was in focus. The qPCR method based on basidiomycete DNA content in the wood had the highest sensitivity, while the ergosterol assay was more sensitive than the chitin assay. Visual rating was compared with laboratory analyses and was found to be correlating well with qPCR. This study demonstrates that qPCR in combination with microscopy provides relevant data about basidiomycete colonization in wooden material.

Abstract

Logging residues, branches and treetops after logging, were considered in the past as unsalable portions of the felled trees and remained on the landing. Currently, logging residues are harvested, stored in piles for variable time periods prior to being utilized as a bioenergy source. However, it is still unclear to what extent the colonization by decay fungi during outdoor storage impairs the fuel quality. Our objective was to find out whether the storage method influenced the amount of basidiomycetous fungi, the main wood degraders in logging residues....

Abstract

Fungal hyphae in soil, although crucial in the C-dynamics, are difficult to quantify. Here we present a simple method for fungal biomass assessment and possibility for up-scaling. Originally we used root nets to quantify fine roots in drought-stressed Picea abies stand as described by Lukac and Godbold (2010).Root nets (7 cm wide, mesh size 1 mm) were inserted vertically to 20 cm depth, twice during the course of one year. When root nets were extracted from the soil, large amounts of hyphae were growing on and through the nets in the control plot, whereas little or no hyphae were growing in nets from the drought-stressed plot.This observation led us to consider root nets as a promising tool to quantify hyphae as well. The inert net material together with its regular geometric pattern is well suited for obtaining fungal biomass estimates and provide a material for further molecular analysis of fungal species. We will describe a proposal how to scan the hyphae, calculate the biomass and upscale to the soil volume unit.

Abstract

This study is a part of a larger project designed to find out the causes of top dieback symptoms in Norway spruce in SE Norway. Because sapwood tracheids constitute a water transport system while parenchyma serves as a reserve tissue (Sellin, 1991), the separation and quantification of the sapwood and heartwood may contribute to understanding of the healthy tree functioning. As the extent of sapwood is related to tree vitality, it reflects the tree growth, health and effect of environmental factors (Sandberg & Sterley, 2009). Therefore, the sapwood cross-sectional area is widely used as a biometric parameter indicating the tree vitality, although its estimation and evaluation is prone to scaling errors....

Abstract

Plants use an array of responses to pathogenic infection. Understanding of the underlying defence mechanisms may lead to new strategies for reducing the damage. Our objective here was to study histological and cytological responses in Norway spruce of different ages (from seedlings to mature trees) to infection with several pathogenic organisms (Pythium dimorphum, Ceratocystis polonica and Heterobasidion annosum) and compared them to effects of mechanical wounding. To visualize the reaction on infection/wounding we used different histological staining techniques followed by laser confocal microscopy and TEM. Primary roots of Norway spruce seedlings were infected with P. dimorphum, while mature trees (about 30 years old) were infected with C. polonica, H. annosum and wounded. In seedling roots the hyphae of P. dimorphum penetrated the tissue rapidly and colonized the root within 24 hours. In the infected tissue the lignin concentration doubled within 6 days compared to non infected roots. General response to infection by C. polonica and H. annosum in mature trees was the production of lignosuberised wound periderm, accumulation of polyphenolic aggregates in living parenchyma cells in the phloem and development of traumatic resin ducts in the xylem. Upon wounding, we observed a similar, but less intense response. In conclusion, although we tested fungi belonging to different taxonomical and ecological groups, the responses were similar, differing in intensity and timing of the defence response mainly. The response seems to be similar but dependent on the degree of susceptibility in the individual trees and clones.

Abstract

We monitored the effects of the drought stress on 20-year old clones of Norway spruce (Picea abies) by using a range of instrumental methods. On two experimental plots (Hoxmark, Norway, 59°40\"14`N, 10°47\"36`E) the drought was induced in a period between May and October 2009 by removing the throughfall using the rain shelters and trenching. We collected data on soil moisture, stem and branch sap flow, xylem diameter, anatomical and calorimetric analysis of the needles, fine root biomass and dynamics and resistance to pathogens. Standard meteorological data were collected locally throughout the whole period. Here we present the preliminary analysis of sap flow and xylem diameter in a period 1-17 august 2009. The sap flow was measured on stems in the breast height by using the method of stem tissue heat balance (THB, EMS Brno). The values were measured once in 2 minutes and saved as the average of 10 minutes. The fluctuations in xylem diameter was monitored by using the automatic dendrometers DR26 (EMS Brno). We evaluated both diurnal and seasonal dynamics. Preliminary results show a significant difference in shape of diurnal curves of transpiration as well as different time lag among the sap flow and the potential evapo-transpiration. Also the differences in diurnal dynamics of the stem circumference suggested different xylem water potential in stressed and control trees. In the drought-stressed trees the diurnal fluctuation in stem diameter was about 4 times higher and the total stem increment one third lower, com-pared to the control trees.

Abstract

The drought stress presents a significant threat for the forest ecosystems. The climate change brings some extreme climatic conditions including longer and more common periods of the drought into the still more forest stands. Current forest management and consecutively wood processing industry in the Czech Republic is nowadays dependent mostly on the Norway spruce. In the same hand, Norway spruce is probably the most threatened tree species by the climate change. Therefore there is a demand for the suitable methodology to monitor the direct effect of the drought on the trees. Presented publication puts together different methods of the evaluation of the water stress and tries to assess their value for the study of the water stress. Of course, there are dozen of the methods to study the water stress. In this handbook we skipped the difficult and expensive techniques and focused rather on the simple methods, suitable for the field use. Methodology begins with the description of the meteorological measurements with current widely available instrumental techniques (i.e. measurements of the intensity of global radiation, air temperature and humidity, wind speed and precipitation) and continues with the monitoring of the soil water content and soil water potential. Then there is a focus on the direct effect of the water stress on the plant. We began with the plant root system since we believed that the fine roots were the most susceptible part of the tree. The focus was on their morphology, anatomy and biological activity. In the aboveground part of the tree we focused on the development of the hydraulic architecture of the tree on the microscopic level. This theoretical analysis was validated by the in-situ measurements of the sap flow. Direct and immediate effect of the water stress on the plant water status is described in the means of the plant water potential. Similarly to the hydraulic architecture we dealt with both the xylogenesis (on the cellular level) and the stem increment measured (on the tree level) by the logging band dendrometers. Finally we discussed the effect of the plant water status on the mineral nutrition of the tree. To conclude, none of the methods alone can implicate the complexity of the water stress, however the combination of the different views gives rather good insight on the tree condition and enable to predict the further tree development.

Abstract

There is a need to establish new objective and sensitive methods for early detection and quantification of decay fungi in wood materials. Molecular methods have proven to be a useful tool within wood protection issues, however, this field is still poorly explored and so far relatively few have used these methods within the field of wood deterioration. Among the techniques used in the indirect quantification of fungi in decayed wood and building material are chitin and ergosterol assays. DNA-based methods are rarely used for identification in connection with quantification. Access to knowledge about fungal colonisation paterns in different wood substrates would allow further improvement of new products. The aim of this study was to investigate the colonisation pattern of decay fungi in wood samples after six years in soil exposure, in an EN252 test.....

Abstract

In Norway, it is planned to double the stationary use of bioenergy from all sources by up to 14 TWh before 2020, with much of this increase coming from forest resources, including residues like branches and tops (which are not much used today) being removed after tree harvest. This removal will reduce the supply of nutrients and organic matter to the forest soil, and may in the longer term increase the risk for future nutrient imbalance, reduced forest production, and changes in biodiversity and ground vegetation species composition. However, field experiments have found contrasting results (e.g. Johnson and Curtis 2001; Olsson et al. 1996). Soil effects of increased biomass removal will be closely related to soil organic matter (SOM) dynamics, litter quality, and turnover rates. The SOM pool is derived from a balance between above- and below-ground input of plant material and decomposition of both plants and SOM. Harvest intensity may affect the decomposition of existing SOM as well as the build-up of new SOM from litter and forest residues, by changing factors like soil temperature and moisture as well as amount and type of litter input. Changes in input of litter with different nutrient concentrations and decomposition patterns along with changes in SOM decomposition will affect the total storage of carbon, nitrogen and other vital nutrients in the soil. To quantify how different harvesting regimes lead to different C addition to soil, and to determine which factors have the greatest effect on decomposition of SOM under different environmental conditions, two Norway spruce forest systems will be investigated in the context of a research project starting in 2008/2009, one in eastern and one in western Norway, representing different climatic and landscape types. At each location, two treatment regimes will be tested: Conventional harvesting, with residues left on-site (CH) Aboveground whole-tree harvest, with branches, needles, and tops removed (WTH). Input of different forest residues will be quantified post harvest. Soil water at 30 cm soil depth will be analysed for nutrients and element fluxes will be estimated to provide information about nutrient leaching. Soil respiration will be measured, along with lab decomposition studies under different temperature and moisture regimes. Long term in situ decomposition studies will be carried out in the WTH plots using three different tree compartments (needles, coarse twigs, fine roots) decomposing in litter bags, in order to determine their limit value. The structure of the fungal community will be determined by soil core sampling and use of molecular techniques allowing qualitative and quantitative estimation. Understorey vegetation will be sampled to determine the biomass, and the frequency of all vascular plants, bryophytes and lichens will be estimated. After harvesting, replanting will be carried out. Seedling survival, causes of mortality and potential damage, growth, and needle nutrients will be monitored. Results from these studies will be used to identify key processes explaining trends observed in two series of ongoing long-term whole-tree thinning trials. We shall combine knowledge obtained using field experiments with results of modelling and data from the Norwegian Monitoring Programme for Forest Damage and National Forest Inventory. This will help us to predict and map the ecologically most suitable areas for increased harvesting of branches and tops on a regional scale based on current knowledge, and to identify uncertainties and additional knowledge needed to improve current predictions.

Abstract

Minirhizotrons, transparent acrylic tubes inserted in the soil, are well suited for long term, non destructive, in situ observations of fine roots. In minirhizotrons, the fine roots are regularly photographed and the root images are visually evaluated according to their status as living, dead or disappeared. This evaluation gives the background for further statistical treatment to estimate the fine root longevity. It is inherent in the minirhizotron technique that a large group of roots will be described as “disappeared” due to grazing, overgrowing by other roots, unclear images or other reasons. Because the fraction of disappeared roots is substantial in some cases, this has consequences for the interpretation of the longevity results. We processed three years of minirhizotron images from Norway spruce stands in southeast Norway (30 yr old) and northern Finland (60 yr old). Of all processed fine roots 32 and 23% was evaluated as disappeared in Norway and Finland, respectively. When roots labelled as disappeared were pooled together with dead ones, the fine root longevity estimates, using the Kaplan Meier method, decreased almost by a factor of two (401 and 433 days), as opposed to labeling them as censored observations (770 and 750 days for Norway and Finland, respectively). Here we demonstrate how the early decision making on the fine root status bears consequences on the resulting longevity estimates. The implications will be discussed

Abstract

In this study, we surveyed the long term effects of liming and fertilizing in old Scots pine stands on the ectomycorrhiza (ECM) colonization, tree growth and needle nutrient concentration 35 years later. Four mature stands of Scots pine on low productive mineral soil were limed in 1959 and 1964 with total doses of limestone ranging from 3 to 15 Mg ha1 and fertilized with nitrogen (N) in 1970. Thirty-five years after the first liming treatment, all stands were analysed for tree growth and needle nutrient concentrations and two of the stands were also analysed for ECM colonization. ECM colonization increased significantly with liming from 61.5% in the control plots to 88% in the plot with the highest limestone dose...

Abstract

The soil is considered to be the major Carbon (C) sink in boreal forests, thus determination of soil carbon fluxes is essential for reliable C budgets. Especially partitioning of soil and root respiration is a major challenge. Soil respiration (Rs) consists of autotrophic respiration (Ra, respiration of plant roots and of microorganisms living on root-derived organic C in the rhizosphere) and heterotrophic respiration (Rh, respiration of free-living microorganisms during their decomposition of soil organic matter. In our study we attempted to estimate the contribution of roots to soil respiration by a girdling experiment. The study was established in two Norway spruce (Picea abies) stands, 35 and 65 year old, at Nordmoen, southeast Norway. Four quadratic plots (21m x 21m) were chosen within each of the two stands in spring 2006 and within two plots all trees were girdled. To estimate the contribution of root respiration, we measured CO2 efflux within each plot with a PP EGM-4 gas monitor for CO2, at permanently marked spots during two years (2006 and 2007). In the youngest stand in 2006, Rs in the control plots was higher than in the girdled plots at all measurement occasions. During this period, the mean Rs in the girdled plots was 64.9 % of the mean Rs in the control plots. In 2007, the Rs was highest in the girdled plots on most occasions, but the difference was never significant. In the oldest stand, Rs was also highest in the control plots in 2006 and highest in the girdled stand in most cases in 2007, but the difference was never significant. The implications will be discussed.

Abstract

Tree and understorey fine root growth and longevity was determined by minirhizotrone research in northern Finland. The study was made in a 70-year-old Norway spruce stand, growing on a mesic mineral soil site in the Kivalo experimental forest. Three replicate plots were established, and three vertical minirhizotron tubes installed in June 2003 in soil of each of the three plots. The images were taken at monthly intervals (altogether 11 sessions) during the growing seasons 2004, 2005 and 2006. The lengths, diameters and status (new, living, dead, disappeared) of Norway spruce and understorey (mainly shrub) fine roots were recorded. Our data indicates that there were more new roots growing in the upper soil depths (the organic layer) than in the lower soil depths (mineral soil). Roots in the organic layer, however, elongated less than roots in the upper mineral soil. The growth rate was highest in late summer and early autumn. Regarding root longevity, both trees and understorey showed the same trends by root order and soil depth; the average longevity was 14-16 months. The time from death to disappearance was 6-8 months for trees and 2-7 months for understorey. Furthermore, monthly trends of new roots born versus their death and/or disappearance by soil depth are also presented.

Abstract

We investigated whether the stand age affects the life span of tree and understory fine roots (<1mm) in three Norway spruce (Picea abies) stands: 30, 60 and 120-yr-old. In each stand 9 minirhizotrons were installed and images were collected once in a month throughout the growing season during the three years. Norway spruce fine roots in the 30-yr old stand had a life span 401 ± 27 and 341 ± 68 days, and understory 409 ± 162 and 349 ± 142 days, estimated by using the Kaplan Meier survival analysis (KM) and Weibull distribution, respectively...

Abstract

Human-induced and natural stress factors can affect fine roots and ectomycorrhizas. Therefore they have potential utility as indicators of environmental change. We evaluated, through meta-analysis, the magnitude of the effects of acidic deposition, nitrogen deposition, increased ozone levels, elevated atmospheric carbon dioxide, and drought on fine roots and ectomycorrhizal (ECM) characteristics. Ectomycorrhizal colonization was an unsuitable parameter for environmental change, but fine root length and biomass could be useful. Acidic deposition had a significantly negative impact on fine roots, root length being more sensitive than root biomass. There were no significant effects of nitrogen deposition or elevated tropospheric ozone on the quantitative root parameters. Elevated CO2 had a significant positive effect. Drought had a significantly negative effect on fine root biomass. The negative effect of acidic deposition and the positive effect of elevated CO2 increased over time, indicating that effects were persistent contrary the other factors. The meta-analysis also showed that experimental conditions, including both laboratory and field experiments, were a major source of variation. In addition to quantitative changes, environmental changes affect the species composition of the ectomycorrhizal fungal community.

Abstract

In spring 2002, extensive damage was recorded in southeast Norway on nursery-grown Norway spruce seedlings that had either wintered in nursery cold storage or had been planted out in autumn 2001. The damage was characterised by a top shoot dieback. Two visually distinct types of necroses were located either on the upper or lower part of the 2001-year-shoot. Isolations from the upper stem necroses rendered Gremmeniella abietina, while Phomopsis sp. was isolated mostly from the from the lower stem necroses. RAMS (random amplified microsatellites) profiling indicated that the G. abietina strains associated with diseased nursery seedlings belonged to LTT (large-tree type) ecotype, and inoculation tests confirmed their pathogenicity on Norway spruce seedlings. Phomopsis sp. was not pathogenic in inoculation tests, this implying it may be a secondary colonizer. We describe here the Gremmeniella - associated shoot dieback symptoms on Norway spruce seedlings and conclude that the unusual disease outburst was related to the Gremmeniella epidemic caused by the LTT type on large pines in 2001. The role of Phomopsis sp. in the tissue of diseased Norway spruce seedlings is yet unclear.

Abstract

Fine roots (2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors.The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m-2, and that of spruce and pine 297 g m-2 and 277 g m-2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone.The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.

Abstract

Fine root production, respiration, longevity and mortality are the major processes in carbon dynamics of the forest soils. The objective of the present work was to determine fine root biomass, respiration and root longevity. The study was carried out at a ten year-old stand of planted Norway spruce (Picea abies) (a clearcut, dominated by natural regrowth of Scots pine and birch) and three stands of Norway spruce, approximately 30, 60 and 120 years old, during 2001 and 2002. The stands were located at Nordmoen, a plain of sandy deposits in southeast Norway.Root biomass of both trees and understorey vegetation (0-1, 1-2 and 2-5 mm in diameter) in the humus layer and mineral soil horizons (to depth of 60 cm) was sampled by soil coring. Root respiration was performed in situ, by measuring the CO2 of excavated fine roots by using the CIRAS-I portable gas analyser. For the root turnover study, altogether 60 minirhizotrones were installed and images were processed. Root biomass and necromass (g m-2), specific root length (SRL, m g -1), root length density (RLD, cm cm-3), number of root-tips and mean longevity (y) were estimated.Root biomass was 2-3 times higher in the mineral soil than in the humus horizon. Compared with other stands, root biomass, SRL, RLD and the number of root tips were highest in the 30-year-old stand. At the 10 and 120 year-old stands understorey vegetation roots counted for 70 and 40% of total root biomass, respectively. The amount of necromass at 60 year-old stand was about twice as high (45%) compared to other stands.Root respiration (g C/min./g roots) was significantly lowest at 10-year-old stand. Root respiration among 30, 60 and 120 year-old stands was not significantly different, but it was highest in the 60-year-old stand. The respiration varied seasonally, with high peaks during the summer and lower values during the spring and autumn. Fine root longevity of tree and understorey roots at the 10-year-old stand were 1.2 and 1.4 years, respectively.It is concluded that stand age may influence the dynamics of the fine roots. The complexity of influences will be discussed.

Abstract

The minirhizotron technique provides the opportunity to perform in situ measurements of fine root dynamics and obtain accurate estimates of fine root production and turnover. The objective of the present work was to determine the fine root longevity and mycorrhization in a Norway spruce chronosequence. The study was carried out on four stands of planted Norway spruce (Picea abies), approximately 10, 30, 60 and 120 years old, during 2001 and 2002. The stands were located at Nordmoen, a plain of sandy deposits in southeast Norway (60o15 N, 11o06 E). For the root turnover study, altogether 60 minirhizotrones were installed and images were processed.Individual fine roots were identified, their mycorrhization assessed, appearance and possible disappearance dated, and growth in length measured. The data set was subjected to a survival analysis, using a Kaplan-Meier product-limit approach. The minirhizotron samples were stratified according to stand age class, and Coxs F-test was used to analyze differences in survival estimates. The analysis may also be extended to consider other covariates such as tree species (spruce, pine or birch), understory vegetation, or soil depth. Typical survival function estimates will be presented, and the influence of stand age on the mycorrhization and the dynamics of the fine roots will be discussed.

Abstract

Conidia germination of the root pathogen fungi Fusarium sp. and Cylindrocarpon sp. were followed for up to 96 hours in the presence of border cells from newly germinated Norway spruce. The border cells stimulated the conidium germination of both fungi. We postulate that this may be a part of the defence mechanism of Norway spruce against pathogens. The stimulating agent is unknown The stimulating effect was not seen when border cells originated from plants grown in the presence of aluminium

Abstract

In spring 2002, extensive damages were recorded in southeast Norway on nursery-grown Norway spruce seedlings that had either wintered in nursery cold storage or had been planted out in autumn 2001. The damages were characterised by leader shoot dieback and necroses on the upper or lower part of the 2001-year-shoot. Gremmeniella abietina and Phomopsis sp. were frequently isolated from the diseased seedlings. RAMS (random amplified microsatellites) profiling indicated that the G.abietina strains associated with diseased nursery seedlings belonged to LTT (large-tree type) ecotype, and inoculation tests confirmed their pathogenicity on Norway spruce. Based on sequence analysis of the internal transcribed spacer (ITS) regions of ribosomal DNA, the Phomopsis strains associated with diseased seedlings do not represent any characterized Phomopsis species associated with conifers. Phomopsis sp. was not pathogenic in inoculation tests, this implying it may be a secondary colonizer. ITS-based real-time PCR assays were developed in order to detect and quantify Gremmeniella and Phomopsis in the nursery stock. We describe here the Gremmeniella - associated shoot dieback symptoms on Norway spruce seedlings and conclude that the unusual disease outburst was related to the Gremmeniella epidemic caused by the LTT type on large pines in 2001.

Abstract

Border cells from the seedling root tips were added to the conidium suspensions of two soilborne rootpathogens, Fusarium sp. and Cylindrocarpon sp. The presence of border cells in the suspension clearly stimulated germination of fungal conidia. Conidia of Fusarium sp. and Cylindrocarpon sp.started to germinate within 3 hours after inoculation.When border cells were washed off, the stimulating effect disappeared. Addition of malt extract caused similar stimulation as border cells. Germination of conidia was suppressed in Al-treated plants.

Abstract

Cleaning of containers to counteract infection that might cause root dieback should remove old, adhering media and roots that may harbour pathogens. This study investigated seedling growth and the number of viable fungal propagules retained on the container cavity walls as a result of different container cleaning treatments: washing with cold water (ca 8C) only, or in addition with a bath temperature of 60, 70, 80 or 95C for 30 seconds.More fungal propagules were isolated from containers washed in cold water, than from the other treatments. The most frequently isolated fungi were Paecilomyces sp. and Penicillium sp., which are well known saprophytes. Bacteria and yeast did not seem to be affected by the washing.Electron microscopy studies of container cavity walls revealed many organic particles and fungal spores on the walls of coldwashed containers. Among other fungal spores there were visible chains of Paecilomyces spp. spores.Containers that were washed at 80C had some organic debris attached to the cavity walls, but no spores were visible. In used and unwashed containers fungal spores, hyphae and organic debris were found on the container cavity walls. Containers in which the major part of the seedlings previously had suffered from root dieback might have contained a considerable amount of inoculum before washing.Almost 60% of the seedlings grown in unwashed containers had dead or very stunted root systems, whereas about 10% of the seedlings in cold washed containers suffered from severe root dieback. Additional warm water treatment further reduced the root dieback of this group of containers. In unwashed containers in which healthy seedlings had been grown, about 4% seedlings and after cold washing no seedlings with root dieback were observed.The cold washing procedure had a positive effect on seedling height, but there was no additional effect of the warm water treatment. We conclude that cold pressurised washing alone does not provide adequate control of root dieback and that an additional warm water bath of at least 60C is recommended.

Abstract

A rapid and sensitive method was developed to discriminate between Seiridium cardinale and Seiridium cupressi, the fungi causing severe cankers on common cypress in the Mediterranean area. The method amplified sequence variants in the ITS2 region of ribosomal DNA using the polymerase chain reaction (PCR), followed by polyacrylamide gel electrophoresis, to reveal single-strand conformation polymorphism (SSCP) between the two species. The greatest separation pattern was obtained with a gel matrix containing 7-10% formamide and 3-5% glycerol under optimized running conditions, which were found to be 30-40 V at 4-5 degrees C for 4-8 h. Sequence homology among isolates within each of the two species caused no mobility shifts, with all isolates displaying the same migration pattern. A few base differences between S. cardinale and S. cupressi caused markedly different migration patterns, allowing differentiation of the two pathogens. Differences between these fungi at the genetic level are consistent with known data on morphological, physiological and pathogenic characteristics. SSCP analysis constitutes a rapid and easy-to-perform method by which to recognize and distinguish closely related organisms, and has considerable potential for use in diagnosis and taxonomy.

Abstract

A richly illustrated field guide for mushroom-pickers through the four seasons of the year. The book presents 95 high-quality, colour paintings by Aurel Dermek accompanied by descriptions and text by Isabella Brja. The book is written in slovak language, however, the names of fungi are also in English, German, Czech and Hungarian

Abstract

Roots of Picea abies seedlings were inoculated with pathogenic Pythium dimorphum. The ongoing lignification process, the accumulation of lignin, and the distribution of flavanols and condensed tannins (CT), were related to the concurrent visual disease symptoms, hyphal colonization, and cellular changes. The hyphae ramified in both the cortex and the stele within 24 h. Three days after inoculation the concentration of lignin had increased to a level twice that in noninfected tissues. With histochemical staining, the accumulation of lignin and the ongoing lignification were co-located in the inner cortex layer 4-6 days after infection. Comparison of temporal onset of lignification with the timing of the intruding hyphae shows that this defense response occurs too late to effectively prevent the pathogen from spreading. Flavanols and CT were also detected in both infected and noninfected roots.Increased staining of these compounds in infected roots was often detected in the inner cortex. Electron microscopic studies revealed that at least some of these phenolic compounds were localized either as spherules or as a layer appressed to the tonoplast of the central vacuole.

Abstract

Root dieback is a disease affecting seedlings during their first or second growing seasons. It is caused by pathogenic fungi in the rhizosphere in combination with environmental factors that stress the plants. In this thesis the process of root dieback was studied at several levels.The pathogenesis in primary roots of Norway spruce, Picea abies (L.)Karst., challenged with the pathogenic fungus, Pythium dimorphum Hendrix Campbell, was chosen as a model system to study disease development in nurseries, infection process, and host defenee mechanisms.The development of visual disease symptoms was assessed in three different nurseries, where Norway spruce seedlings were inoculatcd with uniform inoculum of either P. dimorphum or Rhizoctonia sp. Among factors tested (irrigation, media, fungicide, inoculated fungi) only the fungal inoculum had significant effeet on viability of seedlings. Application of benomyl fungicide supressed Rhizoctonia spp. but clearly promoted Pythiaeeous fungi.Hyphae of P. dimorphum penetrated the juvenile roots of Norway spruce rapidly and colonized the whole root tissue within 24 hours. Three days after infection, lignin, measured quantitatively as ligninthioglycolic acid, in infected tissues was double the arnount in non-infected tissues. Flavanols and condensed tannins were constitutively present in both infected and non-infected tissues.More than 30 different pathogenesis-rclated (PR) proteins accumulated in root tissues within two days after inoculation. Ten different proteins revealed chitinase activity, three had chitosanase activity and two 6-1,3-glucanase activity. Two of the chitinases were constitutively present, in addition to eight others that only accumulated after infection. Infection-induced chitinases were detectable already the first day after inoculation.Activity of three chitosanases was detected solely in infected roots, from the second day after inoculation. Two 6-1,3-g1ucanases, accurnulated from second and fourth days after inoculati on, respectively.The hypothesis, that proteins (including PR proteins) in Norway spruce are normally complexed with polyphenols and become released upon fungal infection, was forrnulated. It was tested by adding in the extraction buffer of non-infected roots either non-ionic detergent (Triton X-IDO), known to break the non-covalent association of polyphenol-protein complex, or caffeinc, known to release proteins bound in complex with polyphenols by competitively binding to polyphenols.In both cases the amount of released proteins was similar to the amount of PR-proteins accumulated after inoculation with the pathogenic P.dimorphum, thus strongly supporting our hypothesis.We report here on this novel mechanism, detected in roots of a gymnosperm, Norway spruce, and suggest that this can be a strategy in polyphenol-rich species, where this immediate mechanisrn rnay be involved in the first-row defence response.

Abstract

Root dieback disease of Norway spruce (Picea abies) seedlings is a serious problem in Scandinavian forest nurseries. We have chosen spruce seedlings infected with one of the most pathogenic fungi associated with this disease, Pyrhium sp., as an experimental system to study the interaction between root ceUs and fungi. In this experimental system the infection is efficient, resulting in root necrose within 1-2 days, growth retardation and complete wilting within 10 days. Anatomical studies of the infected roots revealed that within 4 days ceU waUs around the inner cortex ceUs were thicker compared to non-infected cells. Staining with methyl red indicated that deposition of lignin or lignin like substances were associated with this thickening of the ceU walls. Neither pectin nor suberin appeared to be deposited in these ceU walls since staining with rhutenium red and Sudan IV were negative.Already1 day after infection several pathogenesis related (PR) proteins with both basic and acidic pIs appeared. Three days after infection the number and amount of PRproteins increased considerably. On the fourth day the num ber of induced proteins were more then 40. The number and also the amount of these proteins remained stable after this day. Two acidic chitinases were present in non-infected roots. Already the first day after infection both of these were strongly induced and were accompanied by four other acidic and two basic chitinases. At day two the activity of the chitinases already mentioned increased and they were accompanied by two chitinases with a more neutral pl. On the third day after infection the chitinase activities stabilized on a steady level This steady state level was maintained to the 10th day. Also 6-1 ,3-glucanases were induced by the infection with Pyrhium sp. While no 6-1 glucanase activity was detected in non-infected roots, one acidic 6-1,3-glucanase was detected the first day after infection. On the second day after infection an additional acidic 6-1,3-glucanase was detected. The number and amount of B-l,3-glucanases, like the chitinases, stabilized on the level of the third day and was maintained unril day 10. These results show that Norway spruce, a gymnosperm, has a response to pathogen infection with many similarities to the angiosperms. They also show that roots respond to the infection in a way similar to the aerial parts.

Abstract

Root dieback of Picea abies (L) Karst., Norway spruce, seedlings is a serious problem in Scandinavian forest nurseries. We have chosen spruce seedlings infected with a pathogenic Pythium sp. isolate as an experimental system to study the interaction between the roots of a gymnosperm and a pathogen at the protein level. In this infection system, necroses on the hypocotyl and browning of the upper part of the roots appear within 2 days. Within 10 days the seedlings are completely wilted. Low pH soluble PR-proteins from infected and uninfected roots have been resolved on isoelectrofocusing (IEF) gels. Chitinases, chitosanases and β-1,3-glucanases have been detected enzymatically after IEF. Our results show that more than 30 different pathogenesis-related (PR) proteins accumulated in roots after pathogen infection. PR proteins of low and high isoelectric points appeared within 2 days after infection. In uninfected plants, only one acidic protein was detected. Eight different isoforms of chitinases accumulated after pathogen infection. Two acidic chitinases were constitutively expressed, and one of these strongly accumulated following pathogen infection. Three chitosanase activities were observed in infected plants, while no chitosanase activity was detected in uninfected plants. Also, no β-1,3-glucanase activity was observed in uninfected plants. One acidic β-1,3-glucanase was detected in infected roots after the second day of infection. A second acidic β-1,3-glucanase of relatively higher pI was detected on the fourth day. To our knowledge, this is the first report describing the response of gymnosperm roots to pathogen infection at the protein level. For the first time, we show that PR proteins accumulating after pathogen infection also include chitosanases. It can be concluded from our results that although gymnosperms are evolutionarily very distant from angiosperms, in terms of the production of PR proteins the response of gymnosperm roots resembles that observed in angiosperms.