Climate and soil explain contrasting intraspecific trait variability of widespread species over a large environmental gradient

Both climatic and edaphic conditions are currently undergoing significant changes on a global scale. Early studies have suggested that climate and soil together shape plant performance. However, establishing a precise theoretical framework to describe trait-environment relationships has proven challenging. Understanding and identifying the patterns and drivers of intraspecific trait variation is crucial for anticipating changes in plant distributions. This study aimed to examine the relative importance of various environmental drivers in explaining intraspecific trait variation for two widespread species, Sophora japonica and Robinia pseudoacacia , across a broad environmental scale spanning from the southeast to the northwest of China. Intraspecific variation in fourteen functional traits accounted for 23.4% of S. japonica and 28.4% of R. pseudoacacia , indicating that these species exhibit a degree of plasticity in response to changing environmental conditions. There were differences in the influence of climatic and edaphic factors on intraspecific trait variation. For both species, hydraulic trait variations were primarily driven by climate during the growth season and climatic seasonality. In comparison, soil chemical properties accounted for a substantial proportion of the variability in leaf economic traits. Our results show that S. japonica and R. pseudoacacia responded differently to variations in climatic factors. In contrast, the impact of soil factors on traits was more consistently observed between these two species. We conclude that soil conditions, like climate, are crucial factors in investigating geographic variation in functional traits and species distributions. Our analysis also highlights that species specificity must be considered when discussing plant adaptability to climate change. These findings provide valuable insights into how and to what extent climatic and edaphic factors influence species distributions by driving the intraspecific trait variability.