Linking soil nutrients and traits to seedling growth: A test of the plant economics spectrum

Abstract

Investigating the link among plant growth rates, traits and local environmental heterogeneity is necessary for understanding forest dynamics and community assembly. Although recent results showed that aboveground traits are key for determining organism’s performance and main resource-use strategies, it is clear that organism performance is influenced by both above- and below-ground traits. However, we have limited understanding about how belowground strategies change in response to soil fertility and determine plant performance. We hypothesize that belowground traits have significant effects on plant performance and that shifts in soil nutrient variability are associated to shifts belowground traits. We tested these hypotheses by surveying plant communities including 3969 seedlings represented by 49 common species over a 10-year period, measured soil nutrients, including total nitrogen (TN), phosphorus (TP) and potassium (TK), and leaf and root traits to examine the links among soil nutrients, traits and growth. We first examined the coordination of leaf and root traits of community level, then used traits to predict individual and species mean height growth rate (RGRh). Finally, we tested for shifts in traits in response to gradients of soil nutrients. We found that community-level traits tended to be multidimensional. Species with acquisitive leaf traits, e.g., high leaf area ratio (LAR), phosphorus content (LP), specific leaf area (SLA) and low leaf dry matter content (LDMC), exhibited high growth rates. However, root traits were weak predictors of RGRh, all root traits were not significantly correlated to RGRh of species, only root tissue density (RTD), specific root area (SRA) and length (SRL) was significantly correlated with RGRh of individuals. Community-weighted mean traits only significantly changed along the gradients of limiting soil nutrients, especially for TK and TP. Species with high LN, SLA, root nitrogen content, SRA and SRL, and low tissue density associated with high TK and TP. Ultimately, multidimensional trait variations, and weak links between root traits and growth only partly support the plant economics spectrum (correlation among traits along one axis), but emphasizes that, beyond root traits, other resource uptake processes of roots should be linked to plant performances. Our findings provide further insights into the understanding of how ecological strategies regulate plant performances and shape potential responses of plant communities to environmental change.