Scaling leaf respiration with nitrogen and phosphorus in tropical forests across two continents

Leaf dark respiration (R_dark) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect R_dark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility. R_dark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in R_dark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO₂ concentration. We found that the site with the lowest fertility (French Guiana) exhibited greater rates of R_dark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of R_dark with the measured leaf traits. Our data indicate that no single universal scaling relationship accounts for variation in R_dark across this large biogeographical space. Variability between sites in the absolute rates of R_dark and the R_dark : photosynthesis ratio were driven by variations in N- and P-use efficiency, which were related to both taxonomic and environmental variability.