Short-term respiration responses to drying–rewetting in soils from different climatic and land use conditions

• Respiration after drying–rewetting (DRW) in soils from humid sites was examined.
• Respiration rates were measured at hourly intervals.
• Soil microbial biomass in humid sites significantly decreased by DRW.
• Soil respiration by DRW did not always show exponentially decaying rates.
• Labile C pool released by DRW would be from dead microbial biomass.

Many surface soils, including those that have rarely experienced dry conditions, may experience more frequent and/or intense drying–rewetting (DRW) events in the future. Such DRW events are likely to induce large and sudden CO2 pulses derived from increased substrate availability owing to their release from non-biomass soil organic C (SOC) and microbial biomass C (MBC); however, few studies have investigated respiration rates following DRW at high time resolutions (e.g., 1 h) or in soils from humid areas. In this study, DRW effects on the dynamics of respiration rates at hourly intervals for 12 h and substrate-induced respiration (SIR) rates were investigated. Soils previously subjected to different DRW frequencies were collected from forest and arable or grassland sites in Japan (humid), Thailand (semi-humid) and Kazakhstan (semi-arid). The relatively humid Japanese and Thai soils were further subjected to five DRW cycles in the laboratory to compare the effects of the first and fifth DRW. Respiration rates after the first and fifth DRW and first DRW to the Japanese and Thai forest soil, respectively, were not fitted by models employing exponentially-decaying functions, and were initially similar to SIR rates. In such cases, C-saturated conditions for surviving microbes would occur probably because of increased substrate availability following release from dead MBC, suggesting the importance of incorporating microbial parameters into SOC models. Respiration rates after DRW to other samples decreased exponentially to a constant rate. In such cases, when increases in the labile and stable C pools by DRW were estimated by the respiration kinetics, the labile C pool would be primarily derived from dead MBC.