Abstract: Clarifying the relative contributions of functional group asynchrony and dominant functional group stability remains important in ecology. Using a biodiversity framework, this study analyzed the spatiotemporal patterns and drivers of the temporal stability of aboveground net primary productivity (ANPP) across Tibetan Plateau grasslands from 2000 to 2022. ANPP stability showed an overall increase with localized declines. A marked "central depression" indicated the vulnerability of the central transitional zone. In terms of biological drivers, dominant functional group stability was the primary biotic predictor of ANPP stability (standardized total effect of 0.80). Its effect was substantially greater than that of functional group asynchrony across ecological subregions. Phylogenetic diversity also showed an independent positive association, consistent with an "evolutionary insurance" effect for system resilience. Solar radiation emerged as an independent predictor, extending the classical two- dimensional water-heat assessment framework. Its association with stability showed a nonlinear threshold response (approximately 2800 MJ m^-2). Relatively high stability was also observed in the low-diversity western arid region. This pattern suggests that species diversity had limited explanatory power for ANPP stability in this observational system, whereas dominant functional group stability played a more important role. Overall, this study highlights the central role of dominant functional groups in maintaining alpine grassland stability and identifies solar radiation as a relevant regulatory factor for differentiated ecosystem management.

Key words: stability, ANPP, dominant fun ctional group stability, asynchrony, phylogenetic diversity, solar radiation, Tibetan Plateau