Effects of water and nitrogen addition on ecosystem respiration across three types of steppe: The role of plant and microbial biomass.

Evaluating the regional variation of ecosystem respiration (R) in its response to the changes of soil water and nitrogen (N) availability is crucial for fully understanding ecosystem carbon (C) exchange and its feedbacks to global changes. Here, we examined the responses of R, plant community aboveground biomass (AB), microbial biomass carbon (MBC) and soil moisture (SM) to water and N addition, using intact soil monoliths from three different temperate steppes along a precipitation gradient, including meadow steppe, typical steppe, and desert steppe in northern China. We found that the meadow steppe held the highest value of R. Water addition significantly enhanced R while N addition had no effect on R in all three ecosystems. The response of R in the typical steppe was more sensitive than the other two ecosystems. The changes of plant community AB exhibited a much stronger explanatory power than that of MBC for R in the typical steppe. In contrast, MBC was the dominant factor explaining the variation of R in the desert steppe and the meadow steppe. These findings contribute to our understanding of regional patterns of ecosystem C exchange under scenarios of global changes and highlight the importance of water availability in regulating ecosystem processes in temperate steppe grasslands.