Plant community traits and functions mediate the biomass trade-off of alpine grasslands along precipitation gradients on the Tibetan Plateau

A better understanding the mechanisms driving plant biomass allocation in different ecosystems is an important theoretical basis for illustrating the adaptive strategies of plants. To date, the effects of habitat conditions on plant biomass allocation have been widely studied. However, it is less known how plant community traits and functions (PCTF) affect biomass allocation, particularly in alpine grassland ecosystems. In this study, community-weighted means (CWM) were calculated at the community level using five leaf functional traits, and the relationships between PCTF and biomass trade-offs were explored using correlation analysis, variation partitioning analysis and structural equation modeling. We found that the trade-off values were greater than zero in both alpine meadow (AM) and alpine steppe (AS) across the Tibetan Plateau, with different values of 0.203 and 0.088 for AM and AS, respectively. Moreover, the critical factors determining biomass allocation in AS were species richness (SR; scored at 0.69) and leaf dry matter content of CWM (CWMLDMC, scored at 0.42), while in AM, the key factors were leaf dry matter content (CWMLDMC, scored at 0.48) and leaf carbon content of CWM (CWMLC, scored at -0.45). In particular, both CWMLDMC and SR in AS, as well as CWMLDMC and CWMLC in AM were primarily regulated by precipitation. In summary, precipitation tends to drive biomass allocation in alpine grasslands through its effects on PCTF, hence highlighting the importance of PCTF in regulating plant biomass allocation strategies along precipitation gradients.