Testing the Growth Rate Hypothesis in Vascular Plants with Above- and Below-Ground Biomass

The growth rate hypothesis (GRH) proposes that higher growth rate (the rate of change in biomass per unit biomass, mu) is associated with higher P concentration and lower C: P and N:P ratios. However, the applicability of the GRH to vascular plants is not well-studied and few studies have been done on belowground biomass. Here we showed that, for aboveground, belowground and total biomass of three study species, mu was positively correlated with N: C under N limitation and positively correlated with P: C under P limitation. However, the N: P ratio was a unimodal function of mu, increasing for small values of mu, reaching a maximum, and then decreasing. The range of variations in mu was positively correlated with variation in C: N: P stoichiometry. Furthermore, mu and C: N: P ranges for aboveground biomass were negatively correlated with those for belowground. Our results confirm the well-known association of growth rate with tissue concentration of the limiting nutrient and provide empirical support for recent theoretical formulations.