Responses of soil respiration and its components to drought stress

Purpose Climate change is likely to increase both intensity and frequency of drought stress. The responses of soil respiration (R-s) and its components (root respiration, R-r; mycorrhizal respiration, R-m; and heterotrophic respiration, R-h) to drought stress can be different. This work aims to review the recent and current literature about the variations in R-s during the period of drought stress, to explore potential coupling processes and mechanisms between R-s and driving factors in the context of global climate change. Results and discussion The sensitivity of soil respiration and its components to drought stress depended on the ecosystems and seasonality. Drought stress depressed R-s in mesic and xeric ecosystems, while it stimulated R-s in hydric ecosystems. The reductions in supply and availability of substrate decreased both auto- and heterotrophic respirations, leading to the temporal decoupling of root and mycorrhizal respiration from canopy photosynthesis as well as C allocation. Drought stress also reduced the diffusion of soluble C substrate, and activities of extracellular enzymes, consequently, limited microbial activity and reduced soil organic matter decomposition. Drought stress altered Q(10) values and broke the coupling between temperature and soil respiration. Under drought stress conditions, R-m is generally less sensitive to temperature than R-r and R-h. Elevated CO2 concentration alleviated the negative effect of drought stress on soil respiration, principally due to the promotion of plant C assimilation subsequently, which increased substrate supply for respiration in both roots and soil microorganisms. Additionally, rewetting stimulated soil respiration dramatically in most cases, except for soil that experienced extreme drought stress periods. The legacy of drought stress can also regulate the response of soil respiration rate to rewetting events in terrestrial ecosystems through changing abiotic drivers and microbial community structure. Conclusions and perspectives There is increasing evidence that drought stress can result in the decoupling of the above-and belowground processes, which are associated with soil respiration. However, studies on the variation in rates of soil respiration and its components under different intensities and frequencies of drought stress over the ecosystems should be reinforced. Meanwhile, molecular phylogenetics and functional genomics should be applied to link microbial ecology to the process of R-s. In addition, we should quantify the relationship between soil respiration and global change parameters (such as warming and elevated [CO2]) under drought stress. Models simulating the rates of soil respiration and its components under global climate change and drought stress should also be developed.