Seed processes alleviate the negative effects of grazing on plant diversity in alpine grasslands

Abstract

The role of soil seed banks in disturbed ecosystems, especially how mixed grazing affects the entire seed fate pathway (production, dispersal, storage) and species turnover/plant diversity, is understudied as most research focuses on single grazing intensities. We conducted a controlled mixed - grazing experiment with yaks and Tibetan sheep at moderate intensity in alpine grasslands of northeastern Qinghai - Tibetan Plateau. We quantified the full seed fate pathway (production, dispersal via seed rain and canopy seed banks, storage in soil seed banks) to explore grazings impact on seed dynamics and plant diversity. Moderate grazing had an asymmetric effect: it increased community - scale seed output but reduced seed transfer to seed rain and soil seed banks. Seed rain positively influenced the soil seed bank, showing a dynamic coupling under grazing. While grazing directly decreased plant α - diversity, the soil seed bank indirectly mitigated this by mediating species turnover. Our study uncovers the complete seed fate pathway under mixed grazing. Dynamic regulation of seed bank inputs, not static storage, is key to plant community responses to chronic disturbance. The soil seed bank acts as a dynamic biodiversity regulator, and herbivore assemblage composition, not just grazing intensity, determines its ecological function.