Land-use change affects the functionality of soil microbial communities: A chronosequence approach in the Argentinian Yungas

Land-use change has drastically reduced the area of pristine forests in tropical and subtropical regions. In NW Argentina, Yungas forests were among the most affected by deforestation for the implementation of agricultural crops. Conversion of forests to croplands modified the structure and function of soil microbial communities, but its effects on soil functionality across time after land-use change are understudied. Therefore, the objective of this study was to analyze the impact of land-use change and time under cultivation on the functionality of microbial communities in these soils. We established a 30-year old chronosequence comprising 4 stages (forest and short-, mid- and long-term agriculture) in 3 independent farms. Together with soil physicochemical properties, we measured microbial biomass carbon, basal respiration, ammonification, acid and alkaline phosphomonoesterase activities, and community-level physiological profiling (CLPP). During the first years of cultivation, the functionality and biomass of soil microbial communities were strongly affected. Compared to forest soils, short-term agricultural soils exhibited a reduction on microbial biomass (∼45%), ammonification (∼67%) and acid phosphomonoesterase activity (∼41%). Moreover, increased basal respiration (up to 94%) and metabolic quotient in those soils suggested radical changes in functionality at the beginning of the chronosequence. However, CLPP evidenced that older agricultural sites had an increased global catabolic response per unit biomass, while it detected no differences in physiological diversity of soil microbial communities along the chronosequence. The lack of differences detected between mid- and long-term agricultural sites, in addition to a reduced inter-site variability, evidences an apparent stabilization and homogenization of soil microbial communities towards the end of the chronosequence. In contrast with physicochemical variables, microbiological variables had a greater performance for characterizing the different stages of the agricultural chronosequence and the impact of land-use change on soil functionality.