Nível do lençol freático é um melhor preditor que nutrientes para assembleias de plantas vasculares em uma floresta de terra firme na amazônia

Abstract

Many species can co-occur in the same habitat, but species-habitat association can be tighter or looser depending on the gradient effect on the species performance. This association commonly leads to ecological specialization that, in plants, involves abiotic factors such as nutrients and water availability. Here we investigated how hydric (Height above the nearest drainage - HAND) and fertility (phosphorus content and the sum of K+, Ca2+ and Mg2+) gradients constrain the distribution of species from six life forms of plant communities in a tropical forest in the Central Amazon. We hypothesized greater biomass life forms would be less specialized based on root depth and span and that nutrients would constrain species more than water since the soils are poor. We estimated the specialization by comparing the observed values of occurrence along the gradients, with distribution expected by the null model for each species. To compare gradients and life forms, we calculated the standard effect (SES) of each species for each gradient. We used SES as the dependent variable in two GLMMs. In the first, we compared the SES values for each gradient (dependent variable) between life forms (independent variable). In the second GLMM we compared the SES values of each life form (dependent variable) among the 3 gradients (independent variables). In both models the family was declared as a random variable to control the number of species among life forms. Water constrained species more – mainly ferns – than fertility. The phosphorus gradient constrained more species than bases, but both constrained lianas and palms the most. Although nutrients have always been considered the greatest determinant to plant species distribution in the Amazon forests, HAND may have the same or even more important at mesoscale. Also, life forms may respond differently depending on the scales of the edaphic gradients analyzed, not necessarily following the pattern based on root depth.