Effects of Stocking Rates and Simulated Precipitation on Soil Respiration in a Stipa breviflora Desert Steppe, Inner Mongolia, China

Abstract

The subject of this study was to understand how grazing and precipitation affect the carbon cycle of grassland ecosystem. The experiment was carried out in a desert steppe of Siziwang Banner, Inner Mongolia, China, and measured CO₂ flux and abiotic factors twice a month during the growing season (July to October in 2016, May to October in 2017). The experiment used a completely randomized block design, involving four different stocking rate treatments [CK, no grazing, (0 sheep unit hm ^–2 half year^–1), light stocking rate (LG, 0.93 sheep unit hm^–2 half year^–1), moderate stocking rate (MG, 1.82 sheep unit hm^–2 half year^–1) and heavy stocking rate (HG, 2.71 sheep unit hm^–2 half year^–1)] with three replicates, and four precipitation treatments [50% reduced precipitation (P1), natural precipitation (P2), 50% increased precipitation (P3) and 100% increased precipitation (P4)] were set up in each stocking rate treatment plot. Results indicated that increased precipitation treatments significantly increased soil water content (SWC) and soil respiration (Rs), and significantly reduced soil temperature (Ts), grazing treatments significantly reduced Ts, the interaction between precipitation and stocking rate had no significant impact on the above indicators; Rs increased with increasing precipitation in the order: P4 > P3 > P2 > P1, Rs exhibited the following order under different stocking rates: CK > LG > MG > HG. There was a strong positive correlation between Rs and SWC, and a negative relationship between Rs and Ts. Our results demonstrate that SWC is the dominant factor affecting Rs, as SWC explained 87.12% of the variation in Rs.