111 research outputs found
Underestimated role of legume roots for soil N fertility
Research ArticleNitrogen (N) is a major fertilizing element for plants.
The distribution of N in legumes is influencing the efficiency of
the next crop. Nitrogen storage in legumes is actually estimated
by N fixation in shoots, whereas there is little knowledge on the
contribution of roots and nodules to legume N and soil N. Here,
we studied the contribution of roots and nodules of grain and
pasture legumes to plant N and soil N in Mediterranean fields.
Experiments were run under rainfed conditions for a 2-year
period in three regions of Portugal. Entire plants including top
plant and visible roots and nodules were sampled at the end of
the growing seasons for grain legumes, sweet and yellow lupine,
and over two harvests in case of pastures. N2 fixation was measured
for grain legumes and pasture legumes using 15N tracing.
Our results show that aboveground N concentration did not vary
among legumes, but differed in the belowground tissues. Field
studies show that 7–11%of total legume N was associated with
roots and nodules. Data also show an allocation of 11– 14 kg N fixed t−1 belowground dry matter in indeterminate
legumes, which represents half the amount of total aboveground
plant. This finding demonstrates that investigation relying only
on shoot Nunderestimates the role of legumes for soil N fertilityinfo:eu-repo/semantics/publishedVersio
Влияние интенсивности механической активации на структуру гексагонального нитрида бора
Изучено влияние интенсивности механической активации на микроструктуру и свойства гексагонального нитрида бора (hBN).Вивчено вплив інтенсивності механічної активації на мікроструктуру і властивості гексагонального нітриду бору (hBN).The mechanical activation intensity effect on the microstructure and properties of hexagonal boron nitride (hBN) has been studied
Nitrogen fixation and growth response of Alnus rubra amended with low and high metal content biosolids
Evolutionary Instability of Symbiotic Function in Bradyrhizobium japonicum
Bacterial mutualists are often acquired from the environment by eukaryotic hosts. However, both theory and empirical work suggest that this bacterial lifestyle is evolutionarily unstable. Bacterial evolution outside of the host is predicted to favor traits that promote an independent lifestyle in the environment at a cost to symbiotic function. Consistent with these predictions, environmentally-acquired bacterial mutualists often lose symbiotic function over evolutionary time. Here, we investigate the evolutionary erosion of symbiotic traits in Bradyrhizobium japonicum, a nodulating root symbiont of legumes. Building on a previous published phylogeny we infer loss events of nodulation capability in a natural population of Bradyrhizobium, potentially driven by mutation or deletion of symbiosis loci. Subsequently, we experimentally evolved representative strains from the symbiont population under host-free in vitro conditions to examine potential drivers of these loss events. Among Bradyrhizobium genotypes that evolved significant increases in fitness in vitro, two exhibited reduced symbiotic quality, but no experimentally evolved strain lost nodulation capability or evolved any fixed changes at six sequenced loci. Our results are consistent with trade-offs between symbiotic quality and fitness in a host free environment. However, the drivers of loss-of-nodulation events in natural Bradyrhizobium populations remain unknown
Phylogenetic Constraints Do Not Explain the Rarity of Nitrogen-Fixing Trees in Late-Successional Temperate Forests
Symbiotic nitrogen (N)-fixing trees are rare in late-successional temperate forests, even though these forests are often N limited. Two hypotheses could explain this paradox. The 'phylogenetic constraints hypothesis' states that no late-successional tree taxa in temperate forests belong to clades that are predisposed to N fixation. Conversely, the 'selective constraints hypothesis' states that such taxa are present, but N-fixing symbioses would lower their fitness. Here we test the phylogenetic constraints hypothesis.Using U.S. forest inventory data, we derived successional indices related to shade tolerance and stand age for N-fixing trees, non-fixing trees in the 'potentially N-fixing clade' (smallest angiosperm clade that includes all N fixers), and non-fixing trees outside this clade. We then used phylogenetically independent contrasts (PICs) to test for associations between these successional indices and N fixation. Four results stand out from our analysis of U.S. trees. First, N fixers are less shade-tolerant than non-fixers both inside and outside of the potentially N-fixing clade. Second, N fixers tend to occur in younger stands in a given geographical region than non-fixers both inside and outside of the potentially N-fixing clade. Third, the potentially N-fixing clade contains numerous late-successional non-fixers. Fourth, although the N fixation trait is evolutionarily conserved, the successional traits are relatively labile.These results suggest that selective constraints, not phylogenetic constraints, explain the rarity of late-successional N-fixing trees in temperate forests. Because N-fixing trees could overcome N limitation to net primary production if they were abundant, this study helps to understand the maintenance of N limitation in temperate forests, and therefore the capacity of this biome to sequester carbon
Day-to-day variation in nitrogenase activity of Alnus incana explained by weather variables: a multivariate time series analysis
Effects of Elevated Oxygen Tensions on Acetylene Reduction in Alnus incana-Frankia Symbioses
Nitrogenase activity decay and energy supply in Frankia after addition of ammonium to the host plant Alnus incana
Enzymes of the tricarboxylic acid cycle and the malate-aspartate shuttle in the N2-fixing endophyte of Alnus glutinosa
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