Carbon and nitrogen contents and isotopic composition among venezuelan plant communities, functional groups and successional stage

Abstract

The main aim was to determine the diversity and differences in the leaf values of carbon (C) and nitrogen (N) contents and natural isotopic composition (δ¹³C and δ¹⁵N) among tropical species from 27 contrasting plant communities, functional groups and the successional status. The high variation in the leaf values of δ¹³C, δ¹⁵N, %N, %C and C:N ratio are related to the high diversity of species, communities and functional groups. Significant results were as follow: δ¹⁵N and %N were negatively correlated with elevation and rainfall. The %C increased with elevation and rainfall. The hightest N content and δ¹⁵N were found in drier communities and the lowest values in the wettest areas following the leaf economics spectrum. The highest mean values of δ¹⁵N was found in annual herbs and the lowest in shrubs and trees. The mean values of δ¹⁵N were higher in disturbed than undisturbed habitats. The highest mean values of δ¹³C occurred in perennial herbs, succulent species, epiphytes and parasites and the lowest in trees, shrubs and vines. The %C was higher in trees and shrubs and lowest in herbaceous species, and higher for species in undisturbed compared to disturbed habitats. Some trends between plant families, physiology, and communities were recorded. The most important conclusions highlight that climate, composition of functional groups, plant families and ultimately the structure of the communities influence the isotopic composition and C and N contents of species. Functional groups contribute to understanding how life diversity in the tropics may reflect biogeochemistry diversity. Classification of communities based on the isotopic composition and C and N of leaves allows partially grouping certain communities according to some general characteristics such as life form composition and geographical areas. The taxonomic composition also partially influenced communities classification and only explains a fraction of the variation determined according to leaf biogeochemistry.