Basin-wide variations in foliar properties of Amazonian forest: phylogeny, soils and climate

Abstract

We analysed 1040 individual trees, located in 62 plots across the Amazon Basin for leaf mass per unit area (<I>M_A</I>), foliar carbon isotopic composition (&delta;¹³C) and leaf level concentrations of C, N, P, Ca, Mg, K and Al. All trees were identified to the species level with the dataset containing 58 families, 236 genera and 508 species, distributed across a wide range of soil types and precipitation regimes. Some foliar characteristics such as <I>M_A</I>, [C], [N] and [Mg] emerge as highly constrained by the taxonomic affiliation of tree species, but with others such as [P], [K], [Ca] and &delta;¹³C also strongly influenced by site growing conditions. By removing the environmental contribution to trait variation, we find that intrinsic values of most trait pairs coordinate, although different species (characterised by different trait suites) are found at discrete locations along a common axis of coordination. Species that tend to occupy higher fertility soils are characterised by a lower <I>M_A</I> and have a higher intrinsic [N], [P], [K], [Mg] and &delta;¹³C than their lower fertility counterparts. Despite this consistency, different scaling patterns were observed between low and high fertility sites. Inter-relationships are thus substantially modified by growth environment. Analysing the environmental component of trait variation, we found soil fertility to be the most important predictor, influencing all leaf nutrient concentrations and &delta;¹³C and reducing <I>M_A</I>. Mean annual temperature was negatively associated with leaf level [N], [P] and [K] concentrations. Total annual precipitation positively influences <I>M_A</I>, [C] and &delta;¹³C, but with a negative impact on [Mg]. These results provide a first basis for understanding the relationship between the physiological functioning and distribution of tree species across Amazonia.