Comunidades microbianas e estoque de carbono e nitrogênio em luvissolo crômico sob diferentes níveis de degradação no semiárido do Brasil

Abstract

Desertification is an aggravating reality in tropical semiarid regions and has been the target of several studies that aim to establish relationships among vegetation, soil type and resident microbiota. In this study, we evaluated the changes in the activities, structure and abundance of microbial communities in chromic Luvisols, located in Pernambuco (Brazil) under different levels of desertification, as well as identified which soil attributes were responsible for shaping the microbial communities, and defied environmental quality indicators for the Caatinga biome. Carbon, nitrogen and phosphorus from soil microbial biomass (C-BMS, N-BMS, P-BMS), soil basal respiration, soil enzymatic activities (alkaline phosphatase and urease), structure and abundance of ribosomal and functional genes were evaluated. Besides, microbial quotient, metabolic quotient, chemical and physical attributes, alkaline phosphatase and urease activity, easily extractable glomalin and total glomalin were also determined. Soil samples were collected in triplicate by soil horizons in three conditions: i- at desertified soil (P1) - Itacuruba (PE); ii- at process of desertification (P2) - Itacuruba (PE) and iii- at preserved secondary Caatinga (P3) -Serra Talhada (PE). We used a multivariate planning analysis to evaluate the influence of chemical, physical and microbiological attributes of Luvisols under desertification levels. In addition to reducing the dimensionality of the data and identifying microbiological indicators of soil quality that responded significantly to desertification, a multivariate analysis was used. 16S rRNA (bacteria), 18S rRNA (fungi), nifH (biological nitrogen fixation), amoA (oxidizing ammonium bacteria - AOB) and phoD (phosphorus solubilization) genes abundance were subjected to variance analysis (One-way ANOVA) and the means compared by Tukey test (p<0.05), as well as for C-BMS, N-BMS, P-BMS, basal respiration, alkaline phosphatase, urease, glomalin and all other soil chemical and physical variables. Desertification almost completely compromised the biological, chemical and physical attributes of Luvisols, this resulted in significant losses in carbon, and nitrogen stocks, especially in the A surface horizon. However, we found that soil depth also influences on soil attributes, so it was not possible to define whether it is the horizon or depth that defines the role of the microbiota. Both the level of desertification and the pedogenetic horizon modeled the structure of microbial communities, however some community overlaps were identified. In the preserved Caatinga condition it was possible to observe a segregation between the superficial and subsurface soil, while in the desertified soil a narrowing of the microbial community was registered. In soil under desertification, depending on the gene evaluated, sometimes resembles the reference, sometimes with the desertified. A large impact on soil carbon stock was highlighted, showing significant reductions that exceed 60% of the amount stored in the studied Luvisols.