Grazing exclusion regulates bacterial community in highly degraded semiarid soils from the Brazilian Caatinga biome

Abstract

Grazing exclusion has been applied as a suitable strategy for soil conservation worldwide, mainly on semiarid soils. However, it is unclear how grazing exclusion reduces the negative effects of overgrazing on the microbial community in the Caatinga biome. In our study, we assessed the bacterial community under three different soil managements in a semiarid region of the Brazilian Caatinga biome, as follows: (a) Native Caatinga vegetation (natural); (b) grazing exclusion (exclusion); and(c) overgrazing (grazed). The bacterial community was assessed through the sequencing of the V4 region of the 16S rRNA gene and analyzed soil chemical and physical properties were correlated with the bacterial community structure. Our results demonstrate that exclusion increases the content of soil carbon and nitrogen, and bacterial diversity, while grazed showed a reduction of 31 and 43% in organic C, compared to exclusion and natural, respectively. However, the changes in bacterial diversity were more expressive in a specific site (No. 1), suggesting that exclusion strategy could be a context-dependent and complex approach to protecting or improving Caatinga soils. Moreover, grazed areas might restrain the potential of bacterial diversity to sustain ecosystem functions since nonbeneficial elements increased in grazed treatments, which presented a negative correlation with the bacterial community. Our study provides novel evidence that high-intensity disturbance by overgrazing could not only reduce soil fertility but it may also restrain bacterial composition, with implications on ecosystem functioning. The Caatinga soil microbiome may be unable to maintain ecosystem services such as plant and animals' development under overgrazing management.

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