Soil carbon release responses to long-term versus short-term climatic warming in an arid ecosystem

Climate change severely impacts the grassland carbon cycling by altering rates of litter decomposition and soil respiration (R-s), especially in arid areas. However, little is known about the R-s responses to different warming magnitudes and watering pulses in situ in desert steppes. To examine their effects on Rs, we conducted long-term moderate warming (4 years, similar to 3 degrees C), short-term acute warming (1 year, similar to 4 degrees C) and watering field experiments in a desert grassland of northern China. While experimental warming significantly reduced average R-s by 32.5% and 40.8% under long-term moderate and short-term acute warming regimes, respectively, watering pulses (fully irrigating the soil to field capacity) stimulated it substantially. This indicates that climatic warming constrains soil carbon release, which is controlled mainly by decreased soil moisture, consequently influencing soil carbon dynamics. Warming did not change the exponential relationship between Rs and soil temperature, whereas the relationship between Rs and soil moisture was better fitted to a sigmoid function. The belowground biomass, soil nutrition, and microbial biomass were not significantly affected by either long-term or short-term warming regimes, respectively. The results of this study highlight the great dependence of soil carbon emission on warming regimes of different durations and the important role of precipitation pulses during the growing season in assessing the terrestrial ecosystem carbon balance and cycle.