Influence of Soil Moisture on Litter Respiration in the Semiarid Loess Plateau

Understanding the response mechanisms of litter respiration to soil moisture in water-limited semi-arid regions is of vital importance to better understanding the interplay between ecological processes and the local carbon cycle. In situ soil respiration was monitored during 2010-2012 under various conditions (normal litter, no litter, and double litter treatments) in a 30-year-old artificial black locust plantation (Robinia pseudoacacia L.) on the Loess Plateau. Litter respiration with normal and double litter treatments exhibited similar seasonal variation, with the maximum value obtained in summer (0.57 and 1.51 μmol m-2 s-1 under normal and double litter conditions, respectively) and the minimum in spring (0.27 and 0.69 μmol m-2 s-1 under normal and double litter conditions, respectively). On average, annual cumulative litter respiration was 115 and 300 g C m-2 y-1 under normal and double litter conditions, respectively. Using a soil temperature of 17°C as the critical point, the relationship between litter respiration and soil moisture was found to follow quadratic functions well, whereas the determination coefficient was much greater at high soil temperature than at low soil temperature (33-35% vs. 22-24%). Litter respiration was significantly higher in 2010 and 2012 than in 2011 under both normal litter (132-165 g C m-2 y-1 vs. 48 g C m-2 y-1) and double litter (389-418 g C m-2 y-1 vs. 93 g C m-2 y-1) conditions. Such significant interannual variations were largely ascribed to the differences in summer rainfall. Our study demonstrates that, apart from soil temperature, moisture also has significant influence on litter respiration in semi-arid regions.