Soil respiration versus vegetation degradation under the influence of three grazing regimes in the Songnen Plain

Abstract

AbstractUnderstanding the effects of ongoing vegetation degradation (due to grazing pressure) on soil respiration provides a basis for managing grazing to improve sustainability of grassland ecosystems in the context of climate change. In a 2‐year field experiment in a meadow ecosystem, vegetation, soil properties, and root and microbial respiration of 2 dominant communities (Leymus chinensis and Chloris virgata) were examined along a vegetation degradation sequence caused by varying grazing pressures. Aboveground biomass, belowground net primary productivity, litter mass, and microbial biomass carbon significantly decreased as ground cover was reduced. For 2 community types, from light degradation to severe degradation (SD), soil organic carbon (SOC), soil total nitrogen, and total phosphorus concentrations decreased by 14.1–15.4%, 10.9–12.3%, and 10.7–11.9%, respectively; and soil bulk density and pH increased by 9.1–9.3% and 4.6–5.2%, respectively. Over 2 years, from light degradation to SD in 2 communities, annual mean root and microbial respiration rate significantly decreased by 35.9–43.5% and 28–34.4%, respectively. Root respiration was more sensitive to vegetation degradation in C. virgata communities compared with L. chinensis communities. However, temperature sensitivity (Q10) for root and microbial respiration did not significantly change as vegetation degraded. These results indicated that (a) vegetation degradation could drive significant soil degradation in this meadow; (b) vegetation degradation restrained soil CO2 efflux, but more largely decreased biomass carbon input into soil, which finally reduced SOC concentration; and (c) vegetation degradation would not change the response of soil CO2 efflux to climate change. To increase SOC storage and maintain grassland sustainability, grazing exclusion was suggested for restoring vegetation in SD sites, with a stocking rate < 2 sheep·ha−1 or rotational grazing recommended. Finally, overseeding with L. chinensis and legumes should enhance forage and livestock production, and soil carbon and nitrogen sequestration, thus preserving grassland sustainability in this meadow ecosystem.