Unraveling the Relationship Between Soil Carbon, Microbiota, and Nutrients: Impacts of Monoculture, Agroecological Cotton, and Conservation Gradients in the Caatinga

To compare soil carbon pools, biological functioning, and fertility across maize monoculture, agroecological cotton systems, and Caatinga vegetation with contrasting conservation status, and to assess whether agroecological systems exhibit intermediate soil conditions between monoculture and preserved Caatinga. Five land-use conditions were compared in Mossoró, Brazil: maize monoculture, cotton intercropped with maize, cotton intercropped with sesame, preserved Caatinga, and secondary Caatinga. Four composite field replicates were sampled at 0–10 and 10–20 cm. Soil organic carbon (SOC), labile carbon, particulate organic carbon (POC), mineral-associated organic carbon (MAOC), carbon stocks, and chemical attributes were evaluated at both depths, Microbial biomass carbon was assessed at both depths, whereas enzyme activities were assessed only at 0–10 cm. Data were analyzed using univariate tests, Pearson correlations, PCA, and PERMANOVA. Maize monoculture was associated with the most altered soil condition, with SOC reductions of 64% and 76% at 0–10 and 10–20 cm, respectively, relative to preserved Caatinga. Labile carbon, POC, MAOC, microbial biomass, and enzyme activities were responsive to land-use differences. Multivariate analyses clearly differentiated land uses, with preserved Caatinga and maize monoculture occupying opposite ends of the gradient and agroecological cotton systems generally showing intermediate conditions. Agroecological systems were associated with partial maintenance of soil carbon pools and biological functioning but did not reach the condition observed under preserved Caatinga. Diversified organic inputs combined with reduced mechanical disturbance may favor soil C conservation and biological functioning in semi-arid agroecosystems. Maize monoculture reduced soil organic carbon by up to 76% relative to preserved Caatinga. Labile, particulate, and mineral-associated carbon were sensitive to land-use differences. Microbial biomass and soil enzymes were sensitive indicators of degradation and recovery. Agroecological cotton has retained more soil carbon and biological functions than monoculture. Agroecological systems showed partial recovery but did not fully match preserved Caatinga.