Microbial regulation of organic matter decomposition at the regional scale
Final Report Abstract
Soil microorganisms, as primary decomposers of SOC, control C storage in terrestrial ecosystems by mediating feedbacks to climate change. Even small changes in microbial SOC decomposition rates at the regional scale have the potential to alter land-atmospheric feedbacks at the global scale. This project was designed to clarify the role of microbial SOC decomposition dynamics in response to climate change factors in two geographically distinct areas and land-use types. The hypothesis was that microbial communities would be adapted to climatic and edaphic conditions specific to each area and to the SOC organic quality in each land-use and would therefore exhibit distinct responses to soil temperature and moisture variations. Strong seasonal dependency was observed in the temperature sensitivities (Q10) of hydrolytic and oxidative enzymes, whereas moisture sensitivity of β-glucosidase activities remained stable over the year. The range of measured enzyme Q10 values was similar irrespective of spatial scale, indicating a consistency of temperature sensitivities of these enzymes at large scales. Enzymes catalyzing the recalcitrant SOC pool exhibited higher temperature sensitivities than enzymes catalyzing the labile pool. In situ enzyme potential explained measured soil respiration fluxes more efficiently than the commonly used temperature-respiration function, supporting the validity of our chosen modeling approach. As shown in the incubation experiment, increasing temperature stimulated respiration, but decreased the total biomass of bacteria and fungi irrespective of substrate complexity, indicating strong stress responses by both over short time scales. This response did not differ between study areas and land-uses, indicating a dominant role of temperature and substrate quality in controlling microbial SOC decomposition. Temperature strongly influenced the responses of microbial groups exhibiting different life strategies under varying substrate quality availability. The abundance of oligotrophs (fungi and gram-positive bacteria) decreased with soil warming, whereas copiotrophs (gram-negative) increased under labile C substrate conditions. Such an interactive effect of soil temperature and substrate quality was also visible at the taxon level, where copiotrophic bacteria were associated with labile C substrates and oligotrophic bacteria with recalcitrant substrates. Which physicochemical and biological factors might explain the observed alterations in microbial communities and their functions in response to climate change drivers at the regional scale was investigated in a further study. Here, it was shown that the soil C:N ratio exerted scale-dependent control over soil basal respiration, whereas microbial biomass explained soil basal respiration independent of spatial scale. Factors explaining the temperature sensitivity of soil respiration also differed by spatial scale; extractable organic C and soil pH were important only at the landscape scale, whereas soil texture as a control was independent of spatial scale. In conclusion, this project provides an enhanced understanding of the response of microbial C dynamics to climate change at large scales by combining field measurements with innovative laboratory assays and modeling tools. Component specific degradation rates of SOC using extracellular enzyme measurements as a proxy, group-specific temperature sensitivities of microbial key players, and the demonstrated scalespecificity of factors controlling microbial processes could potentially improve the predictive power of currently available C models at regional scale.
Publications
- 2013. midDRIFTS-based partial least square regression analysis allows predicting microbial biomass, enzyme activities and 16S rRNA gene abundance in soils of temperate grasslands. Soil Biology and Biochemistry 57, 504-512
Rasche, F., Marhan, S., Berner, D., Keil, D., Kandeler, E., Cadisch, G.
(See online at https://doi.org/10.1016/j.soilbio.2012.09.030) - 2015. Modelling in situ activities of enzymes as a tool to predict seasonal variation of soil respiration from agro-ecosystems. Soil Biology and Biochemistry 81, 291-303
Ali, R.S., Ingwersen, J., Demyan, M.S., Funkuin, Y.N., Wizemann, H.D., Kandeler, E., Poll, C.
(See online at https://doi.org/10.1016/j.soilbio.2014.12.001) - 2016. Partitioning of ecosystem respiration in winter wheat and silage maize - modeling seasonal temperature effects. Agriculture, Ecosystems and Environment 224, 131–144
Demyan, M.S., Ingwersen, J., Funkuin, N.Y., Ali, R.S., Mirzaeitalarposhti, R., Rasche, F., Poll, C., Müller, T., Streck, T., Kandeler, E., Cadisch, G.
(See online at https://doi.org/10.1016/j.agee.2016.03.039) - 2018. Controls on microbially regulated soil organic carbon decomposition at the regional scale. Soil Biology and Biochemistry 118, 59-68
Ali, R.S., Kandeler, E., Marhan, S., Demyan, M., Ingwersen, J., Mirzaeitalarposhti, R., Rasche, F., Cadisch, G., Pol,L C.
(See online at https://doi.org/10.1016/j.soilbio.2017.12.007) - 2018. Response of microbial abundance to substrate complexity under different temperature regimes. Soil Biology and Biochemistry 127, 60-70
Ali, R.S., Poll, C., Kandeler, E.
(See online at https://doi.org/10.1016/j.soilbio.2018.09.010)
