Plant Functional Traits Mediate the Effects of Flooding on Biomass Allocation in Invasive Plant Communities

ABSTRACT Understanding biomass allocation strategies in invasive plants is crucial for developing effective management approaches. However, the mechanisms by which plant functional traits and soil properties influence biomass allocation in invaded communities, particularly in invasion‐prone riparian zones, remain poorly understood. Here, we collected data on functional traits, biomass, and soil factors from invasive (IP) and non‐invasive (NP) plant communities under similar site conditions in the riparian zone of the Three Gorges Reservoir in China during 2021. We examined the roles of plant community traits and soil factors in shaping biomass allocation and evaluated the applicability of the optimal and isometric allocation theories. Results showed that biomass trade‐off values for both IP and NP were greater than zero and increased with elevation, indicating that riparian plants allocate more biomass to aboveground portions to combat flooding, consistent with the optimal allocation theory. Biomass allocation in NP was primarily influenced by soil physicochemical properties (e.g., bulk density and pH), whereas in IP, it was mainly determined by dominant functional traits, such as community‐weighted mean height (CWM_H). The structural equation model explained 78% and 62% of the variation in biomass trade‐off for NP and IP, respectively. Furthermore, it demonstrated that functional traits (e.g., CWM_H) mediated flooding's effects on biomass allocation in invaded communities. These findings underscore distinct allocation strategies between invaded and non‐invaded communities and highlight the importance of trait‐based mechanisms in driving invasive plant success. This study emphasizes the need to consider dominant trait dynamics when managing invasions in flood‐affected riparian systems.