Nutrient covariance between forest foliage and fine roots

Plants face a trade-off in distributing C and nutrients between above- and below-ground resource acquiring tissues. We compiled data on tree foliar and fine root nutrient concentrations from across a range of forest biomes and leaf forms to reveal general patterns in the covariance of nutrients in these tissues, as well as N and lignin concentrations in leaf litter and fine roots. Linear patterns between foliar and fine root tissues for N, P, Ca, and Mg clearly indicate covariance in nutrient concentrations between above- and below-ground resource acquiring tissues. However, concentrations of N and P in foliage were higher than in roots in nearly all cases. Slopes <1 for linear regressions of N and Ca (0.56 and 0.50, respectively) provide support for differential distribution of these nutrients between resource-acquiring tissues. We hypothesize that the allocation of nutrients to foliar and fine root tissues has a dynamic balance similar to C allocation that optimizes acquisition of limiting resources. Initial assessment of this hypothesis indicates that tissue N and P concentrations may be a good predictor of relative nutrient allocation patterns. Concentrations of N in leaf litter were lower than fine root concentrations, apparently the result of substantial resorption of N from senescing leaf tissue, and may alter the contribution of leaf and root litter to nutrient release from these tissues during decomposition. Future studies are required to evaluate how allocation of nutrients between these tissues changes in response to environmental gradients.