Seasonal soil respiration responses to fencing vary by alpine grassland type in the Tibetan Plateau

• Fencing enhances soil microbial activity and root respiration in alpine steppes but has limited effects in meadows. • Soil respiration enhancements from fencing are strongest during growing season, weaker in non-growing season. • Aboveground biomass and nitrogen availability primarily drive respiration changes in alpine meadows. • Underground carbon availability and microbial communities mainly influence respiration in alpine steppes. Fencing is widely applied for grassland restoration on the Qinghai-Tibet Plateau. However, considerable uncertainty remains in how soil respiration (Rs) and its components, autotrophic (Ra) and heterotrophic (Rh) respiration, respond to fencing in different alpine grassland types. This research investigated the impact of fencing on Rs, Rh, and Ra during growing and non-growing seasons in alpine steppe and alpine meadow, and elucidated the underlying biotic and abiotic mechanisms by assessing plant biomass and community data (e.g., species richness, abundance), soil properties and microbial community composition and diversity. Results revealed divergent responses of Rs, Rh, and Ra to fencing between alpine meadow and steppe ecosystems. In the more mesic alpine meadow, fencing significantly enhanced Rh by 19.3% during the growing season, while Rs and Ra remained largely unchanged. The increased growing season Rh rate in alpine meadow was primarily driven by nitrate nitrogen concentrations. In contrast, fencing exerted more pronounced effects in the relatively xeric alpine steppe, where growing season Rs, Rh, and Ra increased by 93.3%, 66.8%, and 234.3%, respectively. During the non-growing season, Rs and Rh also rose by 50.2% and 55.0%. In the steppe, the elevation of Rh across both seasons was strongly related to substrate availability and microbial community composition, whereas the increase in Ra during the growing season was mainly attributed to enhanced plant biomass. Our study highlights the importance of considering grassland type and seasonal dynamics when assessing fencing effects on soil carbon processes, providing insights into mechanisms regulating soil respiration in alpine ecosystems.