Climate change is altering tree species distributions across eastern U.S. forests and, given the central role trees play in carbon (C) and nutrient cycling, such species shifts are expected to impact ecosystem processes. However, our ability to accurately predict the nature and magnitude of these effects is hindered by our limited understanding of how and why species differ in their use of nutrients. Most forests are limited by nutrients, indicating that species’ variation in their acquisition, allocation, and resorption of nutrients may determine how forests respond to climate change. To this end, we assessed nutrient strategy differences among species and across climate and soil types in three eastern U.S. forests and evaluated the degree to which species’ nutrient use traits are coordinated above- and belowground. Specifically, we measured species-specific foliar nutrient resorption and paired these measurements with belowground root production. We hypothesized that species have coordinated above- and belowground nutrient use strategies, such that the C cost of acquiring soil nutrients through root production both reflects and determines the efficiency of nutrient resorption from senescing leaves. Moreover, we expected that nutrient use strategies vary predictably given the type of mycorrhizal fungi the tree associates with (arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi).
Results/Conclusions
Overall, we found species-specific differences in both foliar nitrogen (N) resorption efficiency (p < 0.001) and belowground root production (p < 0.001). Moreover, AM and ECM tree species exhibited distinct nutrient acquisition strategies, with greater root production under ECM compared to AM species (p < 0.001). However, similar mycorrhizal group differences aboveground were not as pronounced and foliar N resorption efficiency did not vary significantly between groups. A weak, but statistically significant, positive relationship was observed between N resorption efficiency and root production (p < 0.001). Notably, foliar N resorption efficiency was positively correlated with foliar N (r2 = 0.27, p = 0.006) and negatively correlated with leaf litter N (r2 = 0.35, p < 0.001). In this way, foliar nutrient resorption is a critical plant nutrient use strategy with important influences on ecosystem processes as it regulates the flux of nutrients from the plant to the soil via leaf litter. This work improves our understanding of how forest community composition drives ecosystem functioning with important implications for forest management in the face of climate change.