A better understanding of soil microbial ecology is critical to gaining an understanding of terrestrial carbon (C) cycle-climate change feedbacks. However, current knowledge limits our ability to predict microbial community dynamics in the face of multiple global change drivers and their implications for respiratory loss of soil carbon. Whether microorganisms will acclimate to climate warming and ameliorate predicted respiratory C losses is still debated. It also remains unclear how precipitation, another important climate change driver, will interact with warming to affect microorganisms and their regulation of respiratory C loss. We explore the dynamics of microorganisms and their contributions to respiratory C loss using a 4-year (2006-2009) field experiment in a semi-arid grassland with increased temperature and precipitation in a full factorial design. We found no response of mass-specific (per unit microbial biomass C) heterotrophic respiration to warming, suggesting that respiratory C loss is directly from microbial growth rather than total physiological respiratory responses to warming. Increased precipitation did stimulate both microbial biomass and mass-specific respiration, both of which make large contributions to respiratory loss of soil carbon. Taken together, these results suggest that, in semi-arid grasslands, soil moisture and related substrate availability may inhibit physiological respiratory responses to warming (where soil moisture was significantly lower), while they are not inhibited under elevated precipitation. Although we found no total physiological response to warming, warming increased bacterial C utilization (measured by BIOLOG EcoPlates) and increased bacterial oxidation of carbohydrates and phenols. Non-metric multidimensional scaling analysis as well as ANOVA testing showed that warming or increased precipitation did not change microbial community structure, which could suggest that microbial communities in semi-arid grasslands are already adapted to fluctuating climatic conditions. In summary, our results support the idea that microbial responses to climate change are multifaceted and, even with no large shifts in community structure, microbial mediation of soil carbon loss could still occur under future climate scenarios.
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Acknowledgments We would like to thank both anonymous reviewers for their careful reviews of the manuscript. This study was conducted as part of a comprehensive research project (Global Change Multi-factor Experiment-Duolun) sponsored by the Institute of Botany, Chinese Academy of Sciences. This study was supported by grants from the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-JC401), the International Foundation for Science (IFS, C/4783-1) and the National Natural Science Foundation of China (30590382/C011108, 30925009). We wish to extend our thanks to the staff of the Duolun Restoration Ecology Experimentation and Demonstration Station for field sampling. We gratefully acknowledge Dr. Jie Bi for soil PLFA extraction, Prof. Shenglei Fu for GC analysis of the PLFA extracts, Dr. Qiong Ding for data analysis, Drs. Jianyang Xia and Yu Liang for their valuable suggestions. We would also like to thank Christine Verhille at the University of British Columbia for her assistance with English language and grammatical editing of the manuscript.
- Carbon utilization
- Microbial biomass
- Microbial community composition
- Respiratory loss of soil carbon
- Semi-arid grassland