A importância das camadas orgânicas para avaliação e preservação da diversidade microbiana dos solos tropicais

Abstract

The microbiota of organic layers (leaves in different stages of decomposition and humus) of Amazonian forest soils represent a community that is still little known. It is known that the change in land use alters the diversity and composition of microorganisms in this system, but so far, little is known about the impacts on microorganisms associated with organic layers. These layers harbor the diversity of microorganisms in the forest and their loss with the forest-pasture conversion results, consequently, in a loss of diversity. This study investigated the richness and diversity of bacteria, fungi and arbuscular mycorrhizal fungi (AMF) contained in organic soil and also in mineral from a forest and pasture in the Amazon, by sequencing 16S rRNA, ITS and 18S rRNA amplicons, respectively. To assess the functionality of the communities present, genes affected in the N cycle were quantified by qPCR (N2 fixers, AOB, AOA and denitrifiers). Layers at different stages of organic matter decomposition were collected from a forest (layer composed of whole leaves - L, fragmented - F, humus - H and mineral soil) and from a pasture (layers L, F, mineral and rhizospheric soil) in the state of Pará, Brazil. Assessing the diversity of organic layers and mineral soil together, the diversity of bacteria and fungi was greater in the pasture and the AMF were not altered. For beta diversity, organic layers were essential to differentiate land use systems. Bacterial, total fungal and AMF communities differed between organic layers and mineral soil, but also between the two systems, forest and pasture. The adaptive groups of the N cycle (except AOB) were more abundant in the F layer of the pasture. These groups were abundant in the H horizon of the forest and, like in the pasture, AOB was also abundant in the L and F leaf layers. Together, these results highlight how the organic layers are a site of high microbial diversity and separate potential for the cycle of N, not only in a forest environment, but also in a pasture.