Hopp til hovedinnholdet

Publications

NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.

2026

To document

Abstract

Genetic differentiation among populations often varies significantly across the genome due to factors such as selection and recombination, resulting in a heterogeneous genomic landscape. However, variation in low‐differentiation regions—genomic valleys—remains poorly understood. Moreover, most insights into plant genomic landscapes come from flowering plants, while comparable genome‐wide studies in other taxa, such as conifers, remain limited. We analyzed whole‐genome sequencing data from 100 individuals of three pine species— Pinus banksiana , Pinus contorta , and Pinus nigra . We found substantial genome‐wide variation in recombination rates, with intergenic regions exhibiting higher recombination than genic regions, and rates decreasing with increasing distance from genes. Recombination rate was negatively correlated with gene length, driven primarily by intron length, suggesting that long introns in conifers may promote the retention of exceptionally long genes by maintaining low recombination in these regions. Genomic scans further revealed that genomic valleys are maintained through either balancing, background, or parallel selection. Additionally, multiple forms of selection were strongly associated with local recombination rate variation, highlighting the significant role of recombination in shaping patterns of genomic differentiation. Our findings provide new insight into the evolution and maintenance of extremely long genes in conifers. Moreover, the results indicate that allopatric selection in regions of low recombination is a major force structuring genomic variation in these species.

To document

Abstract

Background Drought intensity and frequency are increasing under global warming in the boreal forests, and breeding for drought resistance will facilitate adaptation of new planting material to changing climate conditions. We used a tree-ring dataset of 559 individuals to study Scots pine genetic variation and the efficiency of genomic selection of drought-response traits (drought resistance, recovery and resilience), for the first time. From genotyping-by-sequencing (GBS), 31,101 SNPs were generated and used for the study. Results Significant genetic variation was detected for drought-response and other growth, wood-anatomy and wood density traits. Heritability estimates for wood-anatomical traits were higher than those for drought-response and growth traits. Genetic correlations between drought-response and wood-anatomical traits were generally high but mostly nonsignificant. In contrast, drought resistance and recovery showed positive and significant correlations with basal area increment and height. We found that the predictive ability and accuracy for drought-response traits were lower than those for wood-anatomical traits, and were comparable between GBLUP and ABLUP. Greater genetic gain per year can be achieved through genomic selection relative to pedigree-based selection if the generation interval is reduced. Conclusions The positive genetic correlation between drought-response and growth traits will enable simultaneous selection for improved growth and increased drought resistant trees in Scots pine breeding through either pedigreed-based and genomic selection.

Abstract

Ethiopia suffers from severe soil degradation resulting from poor agricultural management practices, deforestation, cultivation on slopes, and heavy, erratic rainfall patterns. This degradation places substantial pressure on smallholder farmers through the loss of topsoil, which reduces soil fertility and diminishes the area of arable land available for cultivation. Smallholder farmers typically practice mixed crop-livestock system, in which animals are often kept on small plots of land during the dry season and fed crop residues, while being allowed to graze on communal lands during the rainy season. Livestock is important to Ethiopian livelihoods, with a large proportion of the population dependent on it. However, the high density of animals, combined with low forage production, exacerbates soil degradation through overgrazing on communal land and increased reliance on crop residues for feed, thereby reducing the return of organic matter to the soils. To address these issues, inclusion of perennial forage mixtures as leys has been proposed as a strategy to both improve livestock feed production and restore degraded soils while preventing further degradation. Plant mixtures, particularly of grasses and legumes, have well-documented benefits to enhance soil organic C (SOC) and nutrient content, reduce the risk of erosion by stabilizing soil structure, and increase forage yields and feed quality. Improved soil nutrient status due to plant inputs also stimulates soil microbial communities, increasing microbial activity and exoenzyme synthesis. This has positive ramifications for soil nutrient cycling and may help remediate degraded Ethiopian soils in low-input agricultural systems. However, the effects of different plant species mixtures in soils with varying chemical and mineralogical composition remain unclear and require further investigations to identify optimal plant mixtures for different soil types. This thesis aims to elucidate the effects of four forage plant species on selected soil parameters in degraded soils from two distinct Ethiopian regions, with a particular focus on soil microbial functions. The thesis comprises three papers, each with focus on different aspects of plant-soil-plant feedbacks in various settings: (I) the effects of plant diversity and biomass on microbial activity and nutrient cycling in a field experiment, (II) the effects of specific plant species inputs on soil microbial nutrient stoichiometry and nutrient cycling under controlled greenhouse conditions, (III) microbial carbon use efficiency (mCUE) in weathered soils under cultivation of perennial forage species in a greenhouse experiment. The thesis is based on three separate experiments: a field experiment in the Amhara and Sidama regions of Ethiopia, and both large- and small-scale factorial experiments in greenhouse using soils sampled from these regions. Two grasses (Urochloa hybrid cv. Cayman and Megathyrsus maximus) and two legumes (Desmodium intortum and Stylosanthes guianensis) were grown in the experiments described in Papers I and II, whereas only U. cv. Cayman and D. intortum were grown in the experiment described in Paper III. Soil chemical and physical characteristics were determined prior to the experimentation for all soils. Microbial nutrient status and its responses to plant input were assessed via analysis of exoenzyme activity (EEA), while specific microbial functions such as nitrification and denitrification were also measured. The plant effect on microbial C-turnover and growth was determined by using the 18O-H2O stable isotope probing (SIP) method, determining mCUE and microbial growth rate. Overall, plant inputs had generally positive effects on soil microbial functions, although responses varied considerably depending on initial soil properties. The strongest effects were typically observed in the more fertile Sidama soils, compared to the less fertile Amhara soils. The magnitude and nature of plant input effects also differed across the three studies. Plant species diversity and biomass had minor effects on soil microbial functions, while U. cv Cayman showed some positive effects on belowground functions in Hawassa soil (Paper I). Legumes, particularly S. guianensis, enhanced EEA which contributed positively to the soil microbial nutrient cycle (Paper II). Plant inputs affected mCUE only in the Sidama soils, with a positive effect of increased plant biomass on mCUE and a negative effect of the U. cv. Cayman × D. intortum mixture on mCUE (Paper III). In summary, the implementation of perennial forage mixtures had positive effects on soil microbial nutrient cycling, with potential long-term effects for soil health. However, these effects were soil-specific, with stronger responses and higher microbial activity in the more fertile, phosphorus (P) rich soils of the Sidama region. The low responsiveness of soil microbes to plant inputs in the Amhara region may be attributed to inherently low P availability. Alleviating P limitation may therefore be necessary before realizing the beneficial effects of perennial forage mixtures in P-limited soils. In addition, site-specific selection of plant species mixtures that can successfully establish and co-exist is recommended to achieve optimal plant performance and effective soil remediation.

Abstract

This conference proceedings paper investigates how forage species and seasonal cuts affect mass balance, dry matter distribution and crude protein recovery in green biorefinery. The study compares timothy, red clover and a grass–clover mixture across seasonal cuts, with focus on pulp, green protein concentrate and brown juice fractions.

To document

Abstract

Aims Ethiopian soils are severely degraded and nutrient depleted, calling for effective remediation strategies. Enhancing soil biological activity through the cultivation of perennial forages may improve soil nutrient cycling and ameliorate soils. The aim of this study was to evaluate specific forage species as to their ability to improve soil biological functions. Methods We set up a fully factorial greenhouse experiment with Ethiopian soils from two regions differing in mineralogy, soil type and climate and tested the effect of two grass species Urochloa cv. ‘Cayman’, Megathyrsus maximus (Mombassa), and two legumes, Desmodium intortum (Greenleaf), Stylosanthes guianensis (Ubon) grown in single stands and mixtures on soil chemical and microbial variables. After 12 weeks of unfertilized growth, we measured soil mineral nitrogen (N), respiration, exoenzyme activities, microbial biomass N and phosphorus and the symbiotic performance of legumes. Results Soils from lower altitude Sidama region had 24% higher soil microbial activity than those from higher altitude Amhara. Aboveground N yield and shoot:root ratios were good indicators for stimulating effects on soil microbial functions, with S. guianensis having the strongest effect. Mixtures did not perform better than single stands. Legumes induced a 15% increase in acid phosphatase (AP) and 34% increase in N-enzyme activity which improved P-supply in three of the four soils. Conclusions AP-activity was stimulated by legumes in all soils but the overall ameliorative effect of perennial forage species appeared to be highly soil dependent. Plant effects on soil biological functions are more pronounced in less acidic soils with higher extractable P.