Microbiota do solo em floresta de terra firme da Amazônia central: teste experimental da contribuição de P pela extinta megafauna

Abstract

The terra firme forests in Central Amazon are limited by phosphorus (P) available in the soil, due mainly to the fact that they are on very old weathered soils, with low nutrients level. In addition, recent work hypothesized that the extinction of the megafauna resulted in P limitation in the forest around the Amazon River, because those animals spread horizontally in the forest P from the varzea areas which received rich sediments from Andes. We tested the hypothesized P limitation by the extinction of the megafauna. We carried out a P addition experiment using doses that were modelled to have been lost annually with the megafuana, an amount that coincides with P recycling in annual litterfall. We chosen 10 randomly locations and then two plots of 1 m × 1 m were established and received one inorganic P in a dose corresponding to 4 kg / ha. This amount equals the value of P that the forest annually returns in the form of litter and near the hypothetical value added per year by megafauna. P addition did not affect the root colonization by mychorriza (TCM) and did not stimulate the microbial biomass or microbial P or extractable soil P. The results indicate that inorganic P perhaps is not the major factor to regulate the TCM and, at least in the doses applied, and it does not stimulate the soil microbiota at least in the dry season, a period of reduced microbial activity. As we did not observe a saturation of the P fractions after fertilizer addition, we conclude that the contribution of the megafauna to P supply for forest is less important than was hypothesized.