Swedish University of Agricultural Sciences

About: Swedish University of Agricultural Sciences is a education organization based out in Uppsala, Sweden. It is known for research contribution in the topics: Population & Soil water. The organization has 13510 authors who have published 35241 publications receiving 1414458 citations. The organization is also known as: Sveriges Lantbruksuniversitet & SLU.

The role of plant diversity and composition for nitrate leaching in grasslands

Abstract: The relationship between plant diversity and nitrate leaching into groundwater was investigated in a mid-European semi-natural grassland ecosystem. An experimental approach was used to directly manipulate plant diversity in the field, while holding other environmental factors constant. Species loss was simulated by establishing grassland communities of 16, 8, 4, 2, 1, and 0 plant species, composed of 3, 2, or 1 functional groups (grasses, legumes, and non-legume herbs). Every diversity treatment was replicated with several different species mixtures. Nitrate leaching was determined by continuous extraction of soil solution below the rooting zone and modeling of seepage rates. The concentration of nitrate in the soil solution was highly variable within each level of diversity. In bare ground plots and several low-diversity mixtures containing legumes, nitrate concentrations were higher than the official European Union threshold value for drinking water of 50 mg/L, with maximum values of up to 350 mg/L measured in Trifolium pratense monocultures. Total annual loss of nitrate was unaffected by the number of plant species or functional groups, but it was highly dependent on the specific species composition of the communities, and plots with legumes lost significantly more nitrate than plots without them. Aboveground biomass had no influence on nitrate loss, whereas leaching was negatively correlated with increasing root biomass. The abundance of legumes within a community, litter decomposition rates, and net nitrification were all positively correlated with total nitrate loss. However, in those communities containing legumes, leaching decreased with increasing diversity, because higher species richness led to a reduction in legume dominance, to a reduced nitrate supply through nitrification, and to a complementary uptake of nitrate by grasses and non-leguminous herbs. Based on these results, we expect that increasing the diversity of non-leguminous species or functional groups would reduce the risk of nitrate leaching in low-diversity grass–clover mixtures of ley-farming systems, while allowing for a more efficient exploitation of the beneficial fertilization effect provided by legumes. Corresponding Editor: M. Loreau.

A transcriptional timetable of autumn senescence

Abstract: Background: We have developed genomic tools to allow the genus Populus (aspens and cottonwoods) to be exploited as a full-featured model for investigating fundamental aspects of tree biology. We have undertaken large-scale expressed sequence tag (EST) sequencing programs and created Populus microarrays with significant gene coverage. One of the important aspects of plant biology that cannot be studied in annual plants is the gene activity involved in the induction of autumn leaf senescence. Results: On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a freegrowing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. Conclusions: We observed a major shift in gene expression, coinciding with massive chlorophyll degradation, that reflected a shift from photosynthetic competence to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilization. Autumn senescence had much in common with senescence in annual plants; for example many proteases were induced. We also found evidence for increased transcriptional activity before the appearance of visible signs of senescence, presumably preparing the leaf for degradation of its components.

Expressed Sequence Tag-Linked Microsatellites as a Source of Gene-Associated Polymorphisms for Detecting Signatures of Divergent Selection in Atlantic Salmon (Salmo salar L.)

Abstract: The prediction that selection affects the genome in a locus-specific way also affecting flanking neutral variation, known as genetic hitchhiking, enables the use of polymorphic markers in noncoding regions to detect the footprints of selection. However, as the strength of the selective footprint on a locus depends on the distance from the selected site and will decay with time due to recombination, the utilization of polymorphic markers closely linked to coding regions of the genome should increase the probability of detecting the footprints of selection as more gene-containing regions are covered. The occurrence of highly polymorphic microsatellites in the untranslated regions of expressed sequence tags (ESTs) is a potentially useful source of gene-associated polymorphisms which has thus far not been utilized for genome screens in natural populations. In this study, we searched for the genetic signatures of divergent selection by screening 95 genomic and EST-derived mini- and microsatellites in eight natural Atlantic salmon, Salmo salar L., populations from different spatial scales inhabiting contrasting natural environments (salt-, brackish, and freshwater habitat). Altogether, we identified nine EST-associated microsatellites, which exhibited highly significant deviations from the neutral expectations using different statistical methods at various spatial scales and showed similar trends in separate population samples from different environments (salt-, brackish, and freshwater habitats) and sea areas (Barents vs. White Sea). We consider these ESTs as the best candidate loci affected by divergent selection, and hence, they serve as promising genes associated with adaptive divergence in Atlantic salmon. Our results demonstrate that EST-linked microsatellite genome scans provide an efficient strategy for discovering functional polymorphisms, especially in nonmodel organisms.

Soil nitrogen form and plant nitrogen uptake along a boreal forest productivity gradient

Abstract: We present results from a study of soil solution concentrations of ammonium (NH4 +), nitrate (NO3 –), and amino acid N over one growing season along a local 90-m-long plant productivity gradient in a boreal forest. Three forest types are found along the gradient: an ericaceous dwarf-shrub type between 0 and 40 m, a low-herb type between 40 and 80 m, and a tall-herb type at 90 m. Soil sampling of the mor layer was performed in June, July, August and October in the three forest types. In addition, plant uptake of NH4 +, NO3 – and the amino acid glycine was investigated. A mixture of the three N forms was injected into the soil; one N form at a time was labeled with 15N, and in the case of glycine also with 13C. In the dwarf-shrub forest, where plant productivity was low, the soil N pool was strongly dominated by amino acid N. There, plants took up more NH4 + than NO3 –. Glycine uptake did not differ significantly from either NH4 + or NO3 – uptake. Along the gradient, soil concentrations of NH4 + and NO3 – increased, as did plant productivity. In the low-herb forest NH4 + comprised a major portion of the soil N pool, and plants took up more NH4 + than NO3 – or glycine. In the tall-herb forest, NO3 – was as abundant as NH4 +, and together these two N forms dominated the soil N pool. Here, plants took up nearly equal amounts of NO3 – and NH4 +, and this uptake exceeded that of glycine severalfold. Apart from the overall preference for NH4 + that plants exhibited throughout the gradient, the results show a correlation between soil concentrations of amino acids and NO3 – and plant preferences for these N forms.

Alterations in Water Status, Endogenous Abscisic Acid Content, and Expression of rab18 Gene during the Development of Freezing Tolerance in Arabidopsis thaliana

Abstract: Treatments as diverse as exposure to low temperature (LT), exogenous abscisic acid (ABA), or drought resulted in a 4 to 5[deg]C increase in freezing tolerance of the annual herbaceous plant Arabidopsis thaliana. To correlate the increase in freezing tolerance with the physiological changes that occur in response to these treatments, we studied the alterations in water status, endogenous ABA levels, and accumulation of rab18 (V. Lang and E.T. Palva [1992] Plant Mol Biol 20: 951-962) mRNA. Exposure to LT and exogenous ABA caused only a minor decline in total water potential ([psi]w), in contrast to a dramatic decrease in [psi]w during drought stress. Similarly, the endogenous ABA levels were only slightly and transiently increased in LT-treated plants in contrast to a massive increase in ABA levels in drought-stressed plants. The expression of the ABA-responsive rab18 gene was low during the LT treatment but could be induced to high levels by exogenous ABA and drought stress. Taken together, these results suggest that the moderate increases in freezing tolerance of A. thaliana might be achieved by different mechanisms. However, ABA-deficient and ABA-insensitive mutants of A. thaliana have impaired freezing tolerance, suggesting that ABA is, at least indirectly, required for the development of full freezing tolerance.