Functional trait relationships have been studied across spatial scales to gain insight into plants adaptations to their environment. Environmental filter theory suggests homogeneity of traits within communities; however, this is not commonly found in nature. To understand trait differentiation among taxa and genotypes within a community, five leaf traits (leaf lifespan (LL), leaf mass per area (LMA), nitrogen concentration in green (Ngreen) and senesced leaves (Nsenesced), nitrogen resorption efficiency (REFF)) and one wood trait (wood density (WD)) of 295 individuals belonging to 45 tree species were studied in a Chinese subtropical forest. We tested (1) whether leaf traits were correlated with each other following “nutrient-conservation” vs. “rapid-growth” strategies, (2) whether leaf traits were correlated with wood traits, and (3) whether these trait correlations themselves could be partitioned into meaningful between- and within-taxa relationships. The measured leaf and wood traits were also tested for the presence of phylogenetic signals. We used correlation networks to display the relationships between traits and partitioned these relationships into different components using hierarchical analysis of covariance. We mapped the traits to the species’ phylogeny, quantified the tendency for related species to be similar (phylogenetic signal) and tested correlated evolution between traits with phylogenetically independent contrasts.
Results/Conclusions
We found negative relationships, i.e. tradeoffs for Ngreen–LMA and Ngreen–LL and positive relationships for LMA–LL within our forest community, in agreement with previous broad-scale studies of between-community relationships. The wood trait WD was correlated with all the leaf traits except Nsenesced. None of the six plant functional traits except Nsenesced were significantly correlated with the additionally measured soil N concentration. Partitioning the relationships into components, we found the above-mentioned ones were stronger between than within species but significant intra-specific tradeoffs could be found for Ngreen–LMA, REFF–LMA. Overall, within-species components explained 12.8–48.5% of the total covariance between traits. All traits related to N concentration and resorption (Ngreen, Nsenesced, REFF) and LMA showed a statistically significant phylogenetic signal. The relationships Ngreen–LMA, Ngreen–LL, Ngreen–WD, Ngreen–REFF, REFF–WD, LMA–LL and LMA–WD showed correlations based on phylogenetic independent contrast, which indicated that most inter-specific components of trait relationships were not phylogenetically conserved. Our findings suggested that within a single community, variation in leaf and wood traits reflects inter-specific trait-correlation networks, with species placed along a strategy spectrum similar to the so-called leaf-economics spectrum reported across large spatial scales.
