Root exudation and associated traits explain the differentiation of plant survival strategy in a drawdown zone in China

Periodic flooding profoundly influences the root adaptation strategies of riparian plants and their soil interactions, with root exudation playing a pivotal role. However, the differentiation of plant survival strategies, driven by the trait syndrome associated with root exudation and the phylogenetic signal, remains unknown under the altered man-made hydrological regime. We selected 19 common herbs in the drawdown zone of the Three Gorges Reservoir (TGR) and comprehensively determined their root exudates and associated morphological and chemical traits in situ. Root exudation emerged as a competitive trait in the root economics space of riparian plants, with minimal influence from phylogenetic signals on the trait syndrome. The root exudation rate of annuals was significantly higher than that of perennials. Annuals were characterized by high specific root length, high specific root area, and high root exudation rate, standing on the fast side of the root conservation gradient. In contrast, perennials were characterized by large root diameter, high root tissue density, low exudation rate, and positioned on the conservative side. Our findings reveal that root exudation is involved in, and likely facilitate, diverse adaptation strategies of different life history plants in the drawdown zone of the TGR. Stress resistance and efficient resource access were the two main dimensions of trait variation in perennials and annuals contributing to their coexistence. Such knowledge will provide important insights into the mechanisms of species coexistence driven by belowground ecological processes and ecosystem responses to heterogeneous environmental change.