Divergent leaf nutrient use strategies of coexistent evergreen and deciduous trees in a subtropical forest

Evergreen and deciduous species co-exist in the subtropical forests in southeastern China. It has been suggested that phosphorus is the main limiting nutrient in subtropical forests, and that evergreen and deciduous species adopt different carbon capture strategies to deal with this limitation. However, these hypotheses have not been examined empirically to a sufficient degree. In order to address this gap in our knowledge, we measured leaf photosynthetic and respiration rates, and nutrient traits related to phosphorus (P), nitrogen (N), and carbon (C) use efficiencies and resorption using 75 woody species (44 evergreen and 31 deciduous species) sampled in a subtropical forest. The photosynthetic N-use efficiency (PNUE), respiration rate per unit N and P (Rd,N and Rd,P, respectively) of the deciduous species were all significantly higher than those of evergreen species, but not in the case of photosynthetic P-use efficiency (PPUE).These results indicated that, for any given leaf P, evergreen species manifest higher carbon use efficiency (CUE) than deciduous species, a speculation that was empirically confirmed. In addition, no significant differences were observed between deciduous and evergreen species for nitrogen resorption efficiency (NRE), phosphorus resorption efficiency (PRE), or N:P ratios. The data indicate that evergreen species coexist with deciduous species and maintain dominance in P limited subtropical forests by maintaining CUE. The data also indicate that it is important to compare the PNUE of deciduous species with evergreen species in other biomes. These observations provide insights into modeling community dynamics in subtropical forests, particularly in light of future climate change.