The root collaboration and leaf economics axes are more consistent than the root conservation axis among individuals, populations, and species

Background & Aims: Comparative functional ecology aims to discover patterns of trait covariation that are consistent and transferable, but recent syntheses have drawn different conclusions about trait relationships. We ask 1) Are bivariate trait tradeoffs that define leaf and root economic axes consistent across ecological scales? 2) Are above- and belowground plant strategies coordinated? 3) Do trait relationships vary interannually or with soil properties? Methods We use trait data collected from 10 graminoid species in a ponderosa pine forest understory. We used linear models and principal components analysis to evaluate bivariate and multivariate trait relationships among individuals, populations, and species. We used data collected in same or different years to test for interannual variability and tested for correlations among root traits and soil characteristics Results We found that trait relationships were consistent for the leaf economics and root collaboration axis, but the root conservation axis was only observed among individuals. The two-dimensional root economic space was not detected, and there were weak correlations between leaf and root traits. We found strong relationships between leaf and root nitrogen when the samples were collected in the same year, but not when data was collected in different years. We found no relationship between soil properties and root traits. Conclusions These results appear to be driven by weak relationships in the root conservation axis. These findings indicate that some proposed tradeoffs remain important at the intraspecific level but that plasticity in nitrogen concentrations can weaken the root conservation axis, especially when measured across years.