In their recent article (Microorganisms and climate change: terrestrial feedbacks and mitigation options. Nature Rev. Microbiol. 8, 779–790 (2010))1, Singh et al. pointed out that the mechanistic basis for predicting the greenhouse gas fluxes under climatic change lies in a detailed understanding of how abiotic and biotic factors affect microbial community dynamics and functions. They highlight that, owing to the vast unexplored diversity of microbiota and the large uncertainty regarding microbial community responses to global change, there are currently no earth system models that have incorporated microbial community dynamics.
We strongly agree with Singh et al. and wish to further highlight that the feedback loop between inorganic nitrogen dynamics and microbial communities (steps 2–4 in Fig. 1) can play a key role in regulating the heterotrophic soil respiration response to global warming, and that this is an important mechanism to be incorporated into global earth system models. For high-latitude ecosystems (that is, tundra and boreal ecosystems), the increase in soil temperature with global warming can substantially enhance the activity of microbial communities, and this will lead to faster decomposition of soil organic matter and more inorganic nitrogen in the soil2,3 (steps 1–3 in Fig. 1). This increase in the soil concentration of inorganic nitrogen may stimulate the production of cellulose-decomposing enzymes but block the production of lignin-decomposing enzymes4. These differential effects on enzyme production may lead to an increase in abundance of the copiotrophic community (containing microorganisms that are characterized by a high growth rate on labile carbon and in a nutrient-rich environment) and a decrease in abundance of the oligotrophic community (containing microorganisms that are characterized by a slow growth rate on recalcitrant carbon and in a nutrient-poor environment)5 (step 4 in Fig. 1). Finally, the change in microbial community structure can have important feedbacks to the carbon cycle by increasing the turnover rates of labile soil carbon pools but decreasing the turnover rates of recalcitrant carbon pools (step 2 in Fig. 1). Thus, the feedback loop between inorganic nitrogen dynamics and microbial communities (steps 2–4 in Fig. 1) could be a key mechanism of regulating soil carbon storage under projected future warming. We may incorporate this mechanism into earth system models by dividing the microbial community into two functional groups6,7: the oligotrophic community, which mainly targets recalcitrant carbon pools, and the copiotrophic community, which mainly targets labile carbon pools.
Many factors can affect the feedback loop between nitrogen dynamics and microbial communities, including climate, vegetation, carbon quality, permafrost (for arctic regions), nitrogen deposition and fixation, and denitrification (Fig. 1). Therefore, to accurately predict soil carbon storage under global warming, we need integrated dynamic ecosystem models of plants, microorganisms and soils, along with a detailed representation of the nitrogen cycle. Although we currently have a good understanding of how nitrogen affects the structure and activity of a microbial community5,8,9, further interdisciplinary studies are needed to better understand the feedback loop between inorganic nitrogen dynamics and microbial communities and to better represent the complex plant–microorganism–soil system in global earth system models.
Singh, B. K., Bardgett, R. D., Smith, P. & Reay, D. S. Microorganisms and climate change: terrestrial feedbacks and mitigation options. Nature Rev. Microbiol. 8, 779–790 (2010).
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This work is funded by the US Department of Energy Office of Science, Office of Biological and Environmental Research (BER) Program.
The authors declare no competing financial interests.
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Xu, C., Liang, C., Wullschleger, S. et al. Importance of feedback loops between soil inorganic nitrogen and microbial communities in the heterotrophic soil respiration response to global warming. Nat Rev Microbiol 9, 222 (2011). https://doi.org/10.1038/nrmicro2439-c1
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