Fine root trait dynamics and their relationships with productivity across grasslands under extreme drought.

Trait plasticity is critical to maintaining grassland productivity under climate change, such as drought. However, few studies have focused on the effects of multiyear extreme drought on community-level fine root traits and their corresponding links to productivity. We experimentally removed 66% of growing season precipitation for four years in meadow, typical, and desert grasslands in northern China and evaluated the effects of multiyear drought on community-weighted means (CWMs) and functional diversity of fine root traits (first-order roots), and their relationships with aboveground net primary productivity (ANPP). We found that, in general, root functional composition (CWMs and functional diversity) showed no significant responses to prolonged, extreme drought across all sites. Additionally, ANPP was positively correlated with CWMs of fine root carbon: nitrogen ratio within and across both control and drought plots, indicating that a high abundance of dominant species with high nitrogen-use efficiency promotes ANPP under droughts. In contrast, we found no significant relationship between functional diversity of fine root traits and ANPP. Our results demonstrate that fine root traits at the community level in semiarid grasslands remain relatively stable in response to long-term extreme drought. These findings provide important insights into the responses of fine root traits to extreme drought and highlight their critical roles in predicting the responses of ecosystem functions in these grasslands.