Altitudinal variation in leaf mass per unit area, leaf tissue density and foliar nitrogen and phosphorus content along an Amazon-Andes gradient in Peru

Background: Leaf traits are important in determining the capacity for a plant to acquire carbon, but few data are available for montane cloud forests in the Andes. Aims: To investigate the changes in leaf traits along a large altitudinal transect (220-3600 m) from lowland to montane cloud forest in Peru. Methods: We determined leaf mass per area (LMA, g m^-2), leaf tissue density (L_d, g cm^-3), and foliar nitrogen (N) and phosphorus (P) content, both on a mass (N_m and P_m, %) and area (N_a and P_a, g m^-2) basis for the most abundant species locally. Results: LMA increased with altitude (62.8-169.4 g m^-2), though overall, LMA was lower than in comparable tropical elevation gradients. N_m declined significantly with altitude (2.39-1.25%, P < 0.05), but N_m contents were higher than in comparable studies. The relatively high N_m and low LMA values are consistent with published global leaf trait datasets. No altitudinal trend for P_m was found; rather, our data highlighted the spatial variability in P_m (and P_a) within and among sites at different elevations. Foliar N:P ratios did not show a trend with altitude and did not indicate N limitation except at 3000 m altitude. Conclusions: Though leaf traits showed altitudinal trends similar to other studies, contrary to the general hypothesis, our data suggest that the tropical montane forests presented here are not N limited.