Carbon availability affects soil respiration response to drying-rewetting cycles in semiarid grasslands of China under nitrogen deposition

Soil carbon (C) availability is an important limiting factor affecting the magnitude of soil respiration with increasing the drying-rewetting cycle number. Previous studies have reported that because of a deficiency in available C, improved nitrogen (N) availability has no effects on soil respiration in semiarid grasslands. However, it is not well understood whether the effects of N availability on soil respiration in response to drying-rewetting cycles is regulated by C availability in semiarid grasslands under N deposition scenarios. A field experiment was conducted in a semiarid grassland of northern China to investigate the response of soil CO2 efflux to drying-rewetting cycles (natural precipitation events) with the addition of labile C (glucose, 48 g C m(-2) a(-1)) and N (NH4NO3, 10 g N m(-2) a(-1)) in August 2014. The drying-rewetting cycle significantly increased soil respiration rate in the treatments with both C and N additions, whereas it did not significantly increase soil respiration rate in the treatments with added N alone. After the first drying-rewetting cycle, a significant increase in soil microbial biomass C (MBC) content was observed in the treatments with both C and N additions but was not observed in the treatment with added N alone. After a series of drying-rewetting cycles, the cumulative CO2 efflux over the observed period was significantly higher in the treatments with both C and N additions than that in the treatment with added N alone. These findings imply that improved N availability during the period of 20 days has no effects on soil respiration in response to the drying-rewetting cycle due to microbial C limitation under N deposition scenarios in a semiarid grassland.