Temperature and plant-available soil phosphorus drive intraspecific variation in plant economic traits of Schima superba across an elevation gradient

The whole-plant economics spectrum (PES) describes coordination between organ-level traits that together determine resource use strategies and is relevant for understanding plant responses to environmental change. Whereas coordination between organs has previously been explored across species, it remains unclear whether patterns observed across species hold within species. In addition, the key driving forces underlying this coordination warrant clarification.

In this study we used univariate (regression analysis) and multivariate (principal components analysis, network analysis) analyses to investigate the environmental drivers of intraspecific trait variation (ITV) and consequently, trait covariation, focusing on leaf and fine root traits. We sampled 60 individuals of Schima superba, a widespread evergreen tree, across five elevations in a subtropical forest in China, measuring traits associated with resource use and capture, including photosynthesis, specific root length and root diameter.

Leaf and root traits were significantly correlated within species, forming a PES. We found that plants at low and high elevation had more resource acquisitive traits than at intermediate elevation. Notably, leaf and root traits, as well as a composite variable that contained both, varied nonlinearly with elevation. Leaf trait variation was driven primarily by temperature, whereas root trait variation and a composite variable containing leaf and root traits, was most strongly influenced by temperature and plant-available soil phosphorus.

Our findings show that the coordinated responses of individual traits to climate and soil properties underlie intraspecific variation in whole-plant resource use strategies across environmental gradients. These findings are contrary to recent studies that have found evidence of decoupling between above- and below-ground traits, which suggests that there is selection for coordination among traits in S. superba. Thus, our study enhances our understanding of the key drivers, as well as the ecological significance of environmentally-driven ITV.