Leaf-level photosynthetic capacity in lowland Amazonian and high-elevation Andean tropical moist forests of Peru.

We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests ( TMFs) in the Andes/western Amazon regions of Peru., We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco ( V_cmax), and the maximum rate of electron transport ( J_max)), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area ( M_a, N_a and P_a, respectively), and chlorophyll from 210 species at 18 field sites along a 3300-m elevation gradient. Western blots were used to quantify the abundance of the CO₂-fixing enzyme Rubisco., Area- and N-based rates of photosynthetic capacity at 25°C were higher in upland than lowland TMFs, underpinned by greater investment of N in photosynthesis in high-elevation trees. Soil [P] and leaf P_a were key explanatory factors for models of area-based V_cmax and J_max but did not account for variations in photosynthetic N-use efficiency. At any given N_a and P_a, the fraction of N allocated to photosynthesis was higher in upland than lowland species. For a small subset of lowland TMF trees examined, a substantial fraction of Rubisco was inactive., These results highlight the importance of soil- and leaf-P in defining the photosynthetic capacity of TMFs, with variations in N allocation and Rubisco activation state further influencing photosynthetic rates and N-use efficiency of these critically important forests. [ABSTRACT FROM AUTHOR]