Wetland conversion to agricultural use is widespread globally, particularly in semi-arid regions. As key indicators of wetland responses to global change, plant diversity and biomass are fundamentally influenced by management practices and plant functional strategies. While existing research has largely focused on aboveground traits, the role of root functional traits in mediating plant diversity and biomass remains poorly understood. This study investigated the predictive value of root functional traits for plant species diversity and biomass across a range of agriculturally managed wetlands in the Songnen Plain of semi-arid China. The management practices included natural wetlands (NW), moderately grazed wetlands (MG), mowed and grazed wetlands (MSG), mowed wetlands (TM), and heavily grazed wetlands (HG). The results demonstrated NW exhibiting the highest biomass but lowest diversity, whereas HG sites displayed the opposite pattern. Root traits also varied significantly across wetland sites. Stepwise regression analysis revealed that root phosphorus content (RPC), root carbon-to-phosphorus ratio (RCPR), and root length (RL) were key predictors of diversity (R² = 0.957), while root carbon content (RCC) and specific root area (SRA) are robust predictors of biomass (R² = 0.762). The partial least squares structural equation model (PLS-SEM) further elucidated two primary pathways by which root functional traits influence diversity and biomass: (1) a direct effect of morphological traits (RL) exerted on diversity, and (2) an indirect effect of morphological traits (SRA, RL) on both diversity and biomass via modulation of root nutrient acquisition traits (RCC, RPC, RCPR). Notably, trade-offs between RL and RPC, together with synergies between SRA and RPC, were associated with reduced diversity but increased biomass. In contrast, synergies between RL and RCC and trade-offs between SRA and RCC exerted negative effects on biomass. In conclusion, integrated root trait combinations and their interactions serve as robust predictors of plant diversity and biomass in agriculturally managed wetlands. These findings advance the theoretical framework for understanding wetland ecological dynamics and provide valuable insights for sustainable resource management in semi-arid regions.
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