LAUSR

Abstract Soil carbon (C) availability may play a crucial role in regulating how soil respiration responds to the increase of nitrogen (N) inputs. However, the related research is sporadic so far and has not adequately verified this speculation or addressed the topic in a widespread temperate grassland ecosystem. This lack of knowledge hinders our further accurate prediction of C emissions from terrestrial ecosystems. To improve our knowledge of the role of soil C resources in regulating Rs responses to N inputs, we established a situ field experiment with three levels of N addition (0, 50, and 100 kg N ha−1 yr−1) and two levels of glucose (G) addition (0 and 480 kg C ha−1 yr−1) to determine the Rs dynamics in a temperate semiarid grassland in China. The results showed that only N addition had no significant effects on Rs as well as microbial biomass C (MBC) during our 168-hour observation period, whereas G addition and G addition together with N addition had positive effects on Rs and MBC. The regression analysis further showed that the cumulative CO2 efflux was significantly positively related to soil MBC concentrations during the 168-hour observation period. Altogether, our findings verify that soil C availability is an important driver affecting the Rs response to N addition. No response of Rs to increased N availability resulting from N input was attributed to microbial C limitation in a semiarid grassland during a 168-hour observation.