Grazing weakens the carbon sequestration capacity of dry temperate grassland ecosystems in Central Asia

Abstract

The impact of grazing on carbon (C) stocks in grasslands is significant and is influenced by grazing management practices and abiotic conditions, both of which are spatially heterogeneous. Here, we used highly-precision meteorological and grassland management data with an improved ecological model (Biome-BGCMuSo) to assess the effects of grazing on C dynamics in dry temperate grasslands in Xinjiang Uygur Autonomous Region, China. Our findings indicate that grasslands in Xinjiang acted as a weak net C sink (0.45 kg C m⁻²) between 1975 and 2020, mainly due to elevated CO₂ concentrations. Mean annual gross primary productivity, net ecosystem production, soil organic carbon (SOC), and vegetation carbon (VegC) were 0.87 kg C m⁻² yr⁻¹, 27.72 g C m⁻² yr⁻¹, 9.14 kg C m⁻², and 0.28 kg C m⁻², respectively. Further investigation revealed that the increase in grazing intensity from 0.42 head ha⁻¹ to 0.73 head ha⁻¹ reduced the C sequestration capacity of grasslands from 0.53 kg C m⁻² to 0.45 kg C m⁻² over the study period under climate change. Most of this reduction resulted from SOC loss, which accounted for 78.07 % of total net C loss (42.46 Tg C in SOC and VegC combined). The magnitude of C loss was positively correlated with grazing intensity. However, environmental factors that promote productivity may mitigate the adverse effects of grazing. Therefore, strategies to protect grassland ecosystems are urgently needed and should extend beyond merely reducing grazing intensity to address the competing priorities of food security and atmospheric CO₂ mitigation.