Microbial substrate stoichiometry governs nutrient effects on nitrogen cycling in grassland soils

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Schleuss, P. M.
Widdig, M.
Borer, E. T.
Crawley, M. J.
Kirkman, K. P.
Seabloom, E. W.
Wragg, P. D.
Spohn, M.
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Biederman, Lori
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Ecology, Evolution and Organismal Biology

The Department of Ecology, Evolution, and Organismal Biology seeks to teach the studies of ecology (organisms and their environment), evolutionary theory (the origin and interrelationships of organisms), and organismal biology (the structure, function, and biodiversity of organisms). In doing this, it offers several majors which are codirected with other departments, including biology, genetics, and environmental sciences.

The Department of Ecology, Evolution, and Organismal Biology was founded in 2003 as a merger of the Department of Botany, the Department of Microbiology, and the Department of Zoology and Genetics.

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Human activities have increased nitrogen (N) and phosphorus (P) inputs in terrestrial ecosystems and altered carbon (C) availability, shifting the stoichiometry of microbial substrates in soils, such as the C:N:P ratios of the dissolved organic matter pool. These stoichiometric deviations between microbial biomass and its substrate may control microbial processes of N cycling. We studied the effects of this stoichiometric mismatch using a full factorial N and P addition experiment replicated in six grassland ecosystems in South Africa, the USA, and the UK. We found that N and P addition changed the dissolved organic matter C:N ratio, but not the C:N ratio of the soil microbial biomass. Compared to P addition, N addition decreased microbial N acquisition via non-symbiotic N2 fixation by -55% and increased microbial N release via net N mineralization by +134%. A possible explanation is that the dissolved elements, e.g., dissolved organic C (DOC) and dissolved total N (DN), serve as the main microbial substrate and its C:N ratio defines whether N is scarce or abundant with respect to microbial demands. If N is available in excess relative to microbial demands, net N mineralization increases. In contrast, when N is scarce, immobilization outweighs release decreasing net N mineralization. However, the activity of leucine aminopeptidases, which decompose peptides, was not affected by nutrient additions. Further, C rather than P availability may control the rates of non-symbiotic N2 fixation in the six studied grassland sites. In conclusion, globally increasing nutrient inputs change processes of microbial N acquisition and release in grassland ecosystems and these changes are largely driven by shifts in substrate stoichiometry.


This is a manuscript of an article published as Schleuss, P. M., M. Widdig, L. A. Biederman, E. T. Borer, M. J. Crawley, K. P. Kirkman, E. W. Seabloom, P. D. Wragg, and M. Spohn. "Microbial substrate stoichiometry governs nutrient effects on nitrogen cycling in grassland soils." Soil Biology and Biochemistry (2021): 108168. doi:10.1016/j.soilbio.2021.108168.

Fri Jan 01 00:00:00 UTC 2021