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Abstract

Extensive green roofs have become a frequently used option for stormwater retention across manydifferent climates including cold and wet regions. Despite the extensive documentation of green rooftechnology for stormwater management, the knowledge about their function and potential use in wetand cold regions is deficient. Using historic data on daily temperature and precipitation in a green roofwater balance model coupled with the Oudin model of evapotranspiration (ET), we evaluated the effects ofmaximum green roof storage capacities (Smax) and ET on stormwater retention along climatic gradientsin Northern Europe. Large differences in potential annual stormwater retention were found betweenlocations, driven by differences in temperature and precipitation amounts. Highest retention in abso-lute values was found for the wettest locations, while the warmest and driest locations showed highestretention in percentage of annual precipitation (up to 58% compared to 17% for the lower range). Alllocations showed a considerable retention of stormwater during summer, ranging from 52% to 91%. Stor-age capacities accepting drought conditions once every 3.3–3.9 year were found to be about 25 mm inthe cold and wet locations increasing to 40–50 mm in the warmer and drier locations. Correspondingstorage capacities to prevent wilting of non-succulent vegetation was on average a factor of 1.5 larger(not including Sheffield and Malmö). Annual retention increased both with an increase in plant wateruse (specific crop factors, Kc) and with an increase in Smax, but was found to be more sensitive to changesin Kcthan to changes in Smax. Hence, ET was the limiting factor for green roof retention capacity in thecold and wet locations, but relatively large changes in evapotranspiration would be needed to have animpact on retention. The potential to use vegetation with higher water use to better restore the storagecapacity between storm-events in these regions was however limited by the risk of permanent wilting ofnon-succulent vegetation, even on the wettest locations. A considerable increase in roof storage capacityand substrate thickness would be required to reduce this risk; still the increase in stormwater retentionwould be marginal.

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Abstract

To predict how the function of urban vegetation and the provision of ecosystem services respond to combinations of natural and anthropogenic drivers, a better understanding of multiple stress interactions is required. This study tested combined effects of moderate levels of drought, soil salinity and exposure to diesel exhaust on parameters of physiology, metabolism, morphology and growth of Pinus sylvestris L. saplings. We found that plant responses were primarily dominated by single stressors and a few two-way interactions. Stressor combinations did not have considerable additional negative effects on plant performance compared to single stressors. Hence, synergistic and antagonistic interactions were rare and additive effects frequent. Drought cycles caused most negative effects, from chlorophyll a fluorescence and epicuticular wax content to growth responses, while soil salinity caused fewer negative effects but contributed to reduction in fine root growth and fluorescence parameters at low air contamination. Interestingly, the air contamination alone had only marginal effects on plant morphology and growth, but contributed an antagonistic effect, dampening the negative effect of drought and salinity on the maximum quantum efficiency of PSII photochemistry (Fv/Fm) and fine root biomass. Although, these effects were moderate, it appears that exhaust exposure had a cross-acclimation effect on plant responses to drought and salinity. We also found that salinity had a negative effect on the accumulation of particulate matter on shoots, illustrating that the plant stress situation can affect the provisioning of certain ecosystem services like pollution attenuation. These findings have implications for the understanding of the complex natural and anthropogenic stress situation of urban, and how to maintain the ecological functions and delivery of ecosystem services.

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Abstract

Nitrogen-limited ecosystems are threatened by extensive spread of broom (Cytisus scoparius (L.) Link), a European leguminous shrub that is invasive in several countries. The establishment of invading species may, however, be suppressed by competition from native vegetation. The neighbor impact of the grass Festuca rubra subsp. commutata Gaudin on the performance of C. scoparius was studied in a greenhouse experiment with different arrival order, under low and high nitrogen supply, and with or without inoculation of nitrogen-fixing bacteria. Aboveground biomass of both species was measured after a six-months establishment period, and after a five-months regrowth period. In both periods, presence of F. rubra reduced the performance of C. scoparius as indicated by negative neighbor-effect intensity indices (NIntA). During the establishment period the competitive impact of F. rubra was highest, when planted before C. scoparius, followed by synchronous and late planting. Inoculation with rhizobia and low fertilization decreased the competitive impact of F. rubra. After cutting and regrowth priority effects of F. rubra were still visible. Interaction between the two study species was not affected anymore by inoculation, but strongly by fertilization, with highest competitive impact of F. rubra on C. scoparius under high nitrogen fertilization. In both study periods biomass of C. scoparius was negatively correlated with biomass of F. rubra. Our study provides knowledge about competition processes, which help to improve conservation and restoration measures regarding the spread of C. scoparius. Early sowing of a native grass can help to suppress the invasive species at an early stage. Competitive impact of the grass might be strengthened by high nitrogen availability.

Abstract

Area-efficient constructed systems for stormwater management and bioretention may involve large fluc-tuations in subsurface water levels. Such fluctuations challenge vegetation by forcing roots to exploredeeper layers to access water during dry periods. In a controlled experiment, we studied growth pat-terns and the ability of Phragmites australis roots to track subsurface water level fluctuations of differingamplitude and frequency in substrates with contrasting water-holding capacity. We found that P. aus-tralis was able to adjust its rooting pattern to considerable subsurface water level fluctuations (to wellbelow 120 cm), but that substrate characteristics can restrict its ability to adjust to larger fluctuations.Fluctuation amplitude was the driving factor for plant growth and biomass allocation responses, whilesubstrate characteristics and fluctuation frequency were less important. When not exposed to large waterlevel fluctuations, P. australis grew larger shoots and only explored intermediate rooting depths. Therewas a negative relationship between root and rhizome biomass, showing a resource-based trade-off andshort-term costs of adjusting rooting patterns to large water level fluctuations. These results indicatethat P. australis is suited for systems with considerable subsurface water fluctuations, but constraints onits flexibility need to be investigated.

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Abstract

Invasive nitrogen-fixing plants drive vegetation dynamics and may cause irreversible changes in nutrient-limited ecosystems through increased soil resources. We studied how soil conditioning by the invasive alien Lupinus nootkatensis affected the seedling growth of co-occurring native plant species in coastal dunes, and whether responses to lupin-conditioned soil could be explained by fertilisation effects interacting with specific ecological strategies of the native dune species. Seedling performance of dune species was compared in a greenhouse experiment using field-collected soil from within or outside coastal lupin stands. In associated experiments, we quantified the response to nutrient supply of each species and tested how addition of specific nutrients affected growth of the native grass Festuca arundinacea in control and lupin-conditioned soil. We found that lupin-conditioned soil increased seedling biomass in 30 out of 32 native species; the conditioned soil also had a positive effect on seedling biomass of the invasive lupin itself. Increased phosphorus mobilisation by lupins was the major factor driving these positive seedling responses, based both on growth responses to addition of specific elements and analyses of plant available soil nutrients. There were large differences in growth responses to lupin-conditioned soil among species, but they were unrelated to selected autecological indicators or plant strategies. We conclude that Lupinus nootkatensis removes the phosphorus limitation for growth of native plants in coastal dunes, and that it increases cycling of other nutrients, promoting the growth of its own seedlings and a wide range of dune species. Finally, our study indicates that there are no negative soil legacies that prevent re-establishment of native plant species after removal of lupins.

Abstract

Plant responses to elevated CO2 are governed by temperature, and at low temperatures the beneficial effects of CO2 may be lost. To document the responses of winter cereals grown under cold conditions at northern latitudes, autumn growth of winter wheat exposed to ambient and elevated levels of temperature (+2.5°C), CO2 (+150 µmol mol-1), and shade (-30%) was studied in open-top chambers under low light and at low temperatures. Throughout the experiment, temperature dominated plant responses, while the effects of CO2 were marginal, except for a positive effect on root biomass. Increased temperature resulted in increased leaf area, total biomass, total root biomass, total stem biomass, and number of tillers, but also a lower content of total sugars and a weaker tolerance to frost. The loss of frost tolerance was related to the larger size of plants grown at elevated temperature. The 30% light reduction under shading did not affect the growth, sugar content, or frost tolerance of winter wheat. At the low temperatures found at high latitudes during autumn, the atmospheric CO2 increase is unlikely to enhance autumn growth of winter wheat to any significant extent, while a temperature increase may have important and major effects on its development and growth.

Abstract

Twelve fertilizer/biostimulant products or product families were compared with mineral fertilizer in three two-year trials on USGA greens and sand-based football fields in southern Norway. Within each trial, all treatments were received the same amount of total nitrogen per year. Substitution of some of the mineral fertilizer with Gro-Power® improved turfgrass quality in one trial. Otherwise, the organic fertilizers and biostimulants producted results that were equal to or inferior to the control treatment. In conclusion, fertilization of sand-based golf greens and football fields ought to be based on light and frequent applications of mineral fertilizer throughout the growing season. Organic fertilizers and biostimulants can, at best, be supplements to such a fertilizer program.