Stoichiometric homeostasis of soil microorganisms as a driver of element cycling in grasslands
Final Report Abstract
Cycling of carbon (C), nitrogen (N), and phosphorus (P) at the ecosystem scale is largely driven by soil microorganisms. The aims of the project were to explore how the cycles of C, N and P are interrelated in grassland soils and to test to which extent processes of C, N and P cycling can be explained and predicted by the relationship between the microbial biomass C:N:P ratio and the C:N:P ratio of the available element pool in soils. For this purpose, we studied N and P addition experiments in grasslands on four continents, most of them being part of the Nutrient Network, which is a globally-coordinated element addition experiment. Across grasslands on different continents, the soil microbial biomass C:N:P ratio did not change in response to high chronic N inputs, despite changes in the microbial community composition. Carbon and N mineralization, turnover of elements in the microbial biomass, enzyme activity, and N2 fixation by free-living microorganisms responded to changes in the ratio of available elements in soil as predicted. This indicates that the stoichiometric framework is useful for understanding and predicting changes in the turnover of organic C, N and P and in microbial N2 fixation in response to changes in the ratio of available elements. Further, we found that soil microbial carbon use efficiency did not change in response to nutrient inputs to soil, which suggests that this variable is less important than expected for maintenance of microbial biomass stoichiometry. In addition, we observed that high chronic nutrient inputs led to a decrease in the abundance of phosphorus-solubilizing bacteria, which could not be predicted based on stoichiometric considerations and indicates a loss of functional traits due to high N inputs to grasslands. Furthermore, we showed that synergistic growth of plants in grasslands in response to combined NP addition is caused by increased rates of P cycling under increased N availability. In contrast, N2 fixation by legumes was strongly reduced in response to N and combined NP inputs to grasslands due to a reduction in legume biomass. Taken together, the results gained in the Emmy Noether project contribute substantially to a better understanding of the interrelatedness of C, N and P cycling in grassland ecosystems.
Publications
- (2017) Turnover of carbon and phosphorus in the microbial biomass depending on phosphorus availability, Soil Biology and Biochemistry, 113, 53-59
Spohn, M; & Widdig, M.
(See online at https://doi.org/10.1016/j.soilbio.2017.05.017) - (2019). Addition of inorganic phosphorus to soil leads to desorption of organic compounds and thus to increased soil respiration, Soil Biology and Biochemistry, 130, 220-226
Spohn, M., & Schleuss, P. M.
(See online at https://doi.org/10.1016/j.soilbio.2018.12.018) - (2019): Stoichiometric controls of soil carbon and nitrogen cycling after long-term nitrogen and phosphorous addition in a mesic grassland in South Africa. Soil Biology and Biochemistry, Volume 135, August 2019, Pages 294-303
Schleuss, P. M., Widdig, M., Heintz‐Buschart, A., Kirkman, K., Guhr, A., Martin, S., & Spohn, M.
(See online at https://doi.org/10.1016/j.soilbio.2019.05.018) - (2020). Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus. Global Change Biology, 26(8), 4169-4177
Spohn, M.
(See online at https://doi.org/10.1111/gcb.15154) - (2020). Interactions of nitrogen and phosphorus cycling promote P acquisition and explain synergistic plant‐ growth responses. Ecology, 101(5), e03003.
Schleuss, P. M., Widdig, M., Heintz‐Buschart, A., Kirkman, K., & Spohn, M.
(See online at https://doi.org/10.1002/ecy.3003) - (2020). Microbial carbon use efficiency in grassland soils subjected to nitrogen and phosphorus additions. Soil Biology and Biochemistry, 146, 107815
Widdig, M., Schleuss, P. M., Biederman, L. A., Borer, E. T., Crawley, M. J., Kirkman, K. P Seabloom, E.W., Wragg, P., & Spohn, M.
(See online at https://doi.org/10.1016/j.soilbio.2020.107815) - (2020). Phosphorus and carbon in soil particle size fractions: A synthesis. Biogeochemistry, 147(3), 225-242
Spohn, M.
(See online at https://doi.org/10.1007/s10533-019-00633-x) - (2021) Microbial substrate stoichiometry governs nutrient effects on nitrogen cycling in grassland soils. Soil Biology and Biochemistry
Schleuss, P. M., Widdig, M., Biederman, L. A., Borer, E. T., Crawley, M. J., Kirkman, K., Seabloom, E. W., Wragg, P. D., & Spohn, M.
(See online at https://doi.org/10.1016/j.soilbio.2021.108168)
