Overgrazing‐Induced Root Carbohydrate Depletion During Winter Dormancy Drives the Decline of Stipa purpurea Populations in the Tibetan Alpine Steppe

Plant carbon allocation and physiology are influenced by overgrazing during the growth period. However, the response of plant physiological processes to overgrazing during winter dormancy remains unclear. We analyzed root physiological processes of Stipa purpurea in winter dormancy across three plots: over grazing (FG), exclusions of 2 years (EX2) and 5 years (EX5), using physiological indicators, transcriptomics, and proteomics. The content of fructose, sucrose, and total soluble sugar in S. purpurea roots during the winter dormancy significantly increased in FG, while starch content notably decreased in FG. Transcriptomic and proteomic analyses identified the most differentially expressed genes (DEGs) and proteins (DEPs) that showed an upward trend in FG compared to EX2 and EX5. Key pathways among DEGs and DEPs included glycolysis/gluconeogenesis, pentose phosphate pathway, and glyoxylate and dicarboxylate metabolism. In FG, genes related to hexokinase and pyruvate kinase in glycolysis/gluconeogenesis were up‐regulated compared to EX2 and EX5. These results suggest that roots in FG consume more carbohydrates to generate energy and resist alpine stress during the dormant season. Additionally, the up‐regulation of genes in the tricarboxylic acid cycle pathway in FG indicated increased pyruvate consumption for energy production. The enrichment of glyoxylate and dicarboxylate metabolism contributed to osmoregulation and the clearance of reactive oxygen species. Overgrazing resulted in reduced carbohydrate storage to roots during the growing season and increased carbohydrate consumption during winter dormancy, potentially affecting S. purpurea regrowth the following year and ultimately leading to its decline. Therefore, adjusting grazing intensity to minimize disturbance to key physiological processes is an effective strategy for protecting dominant grass species and maintaining grassland ecosystem stability.