Leaf-branch-root trait relationships in Quercus rehderiana across rocky and non-rocky desertification habitats in China

Background Plant leaves, branches, and roots synergistically govern survival, growth, and reproduction. However, while interspecific and community-level studies have advanced our understanding of organ coordination, intraspecific trait covariation remains poorly understood due to limited evidence. Methodology This study investigated 28 functional traits across leaves, branches, and roots of Quercus rehderiana , a dominant species in rocky and non-rocky desertification forests, to evaluate intraspecific organ relationships. The traits, covering morphological, anatomical, and physiological aspects, reflect resource acquisition and utilization strategies. Standardized protocols were followed, with three replicates per individual for reliability. Results Our results revealed no significant correlations among leaf, branch, and root traits in either forest type. Principal component analysis (PCA) of leaf traits indicated that the first axis was positively associated with water storage and utilization strategies, showing positive correlations with leaf thickness (LT), palisade mesophyll thickness (PT), and spongy mesophyll thickness (ST). The second axis exhibited a positive relationship with leaf nitrogen concentration (LNC) and leaf phosphorus concentration (LPC). For branch traits, the first axis reflected water transport efficiency, demonstrating positive associations with theoretical hydraulic conductivity ( K t ) and vessel density (VD). The second axis was positively correlated with branch N concentration (BNC) and branch phosphorus concentration (BPC). In root traits, the first axis aligned with root defense traits (positive correlation) but was inversely related to resource acquisition efficiency. The second axis showed a positive correlation with root N concentration (RNC) and root phosphorus concentration (RPC). Conclusions Organ-specific trait decoupling in Quercus rehderiana reveals independent above- and belowground adaptations to water and nutrient limitations, challenging whole-plant economic spectrum assumptions. While consistent in rocky desertification forests, they differ from other ecosystems, highlighting context-dependence. Future research should expand across environmental gradients to disentangle trait relationships. This work highlights multidimensional approaches in functional ecology for understanding plant adaptation.