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Amino acids have been shown to be a potentially significant N source for the alpine sedge, Kobresia myosuroides. We hypothesised that freeze-thaw and dry-rewet events allow this plant species increased access to amino acids by disrupting microbial cells, which decreases the size of competing microbial populations, but increases soil amino acid concentrations. To test this hypothesis, we characterized freeze-thaw and dry-rewet events in the field and simulated them in laboratory experiments on plant-soil microcosms. In one experiment, 15N,13C-[2]-glycine was added to microcosms that had previously been subjected to a freeze-thaw or dry-rewet event, and isotopic concentrations in the plant and microbial fractions...
A positive role for biodiversity is assumed for managed ecosystems. We conducted a 12-year study of this sustainability principle, through separate manipulation of management intensity and crop diversity. The site was located in southwest Michigan, representative of rain-fed production, with high climate variability and well-drained soils. Provisioning services of grain and protein yield were monitored, simultaneous with supporting services of soil fertility, C and N, and regulating services associated with water quality (N-use efficiency and nitrate-N leached in gravimetric lysimeters). Surprisingly, a strong role for management was shown, and almost nil for crop diversity. Organic management (ORG) sustained soil...
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The exotic annual grass Bromus tectorum has replaced thousands of hectares of native perennial vegetation in semi-arid ecosystems of the western United States. Inorganic N availability and production were compared in soil from monodominant patches of Bromus tectorum, the perennial bunchgrass Elymus elymoides, and the shrub Artemisia tridentata, in Curlew Valley, a salt-desert shrub site in Northern Utah. Bromus-dominated soil had greater %N in the top 10 cm than Artemisia or Elymus-dominated soils. As determined by spring isotope-dilution assays, gross mineralization and nitrification rates were higher in Bromus-dominated than Artemisia-dominated soils, but gross rates of NH4+ and NO3- consumption were also higher....
Microbial activities drive the global nitrogen cycle, and in the past few years, our understanding of nitrogen cycling processes and the micro-organisms that mediate them has changed dramatically. During this time, the processes of anaerobic ammonium oxidation (anammox), and ammonia oxidation within the domain Archaea, have been recognized as two new links in the global nitrogen cycle. All available evidence indicates that these processes and organisms are critically important in the environment, and particularly in the ocean. Here we review what is currently known about the microbial ecology of anaerobic and archaeal ammonia oxidation, highlight relevant unknowns and discuss the implications of these discoveries...
    map background search result map search result map Inorganic N turnover and availability in annual- and perennial-dominated soils in a northern Utah shrub-steppe ecosystem Inorganic N turnover and availability in annual- and perennial-dominated soils in a northern Utah shrub-steppe ecosystem