Effects of winter and summer conditions on Cd fractionation and bioavailability, bacterial communities and Cd phytoextraction potential of Brachiaria decumbens and Panicum maximum grown in a tropical soil

The interactions between soil properties, microorganisms, plant species and climate affect cadmium (Cd) availability in tropical soils. In this study, we investigated the effects of simulated summer and winter conditions on Cd fractionation and bacterial communities in Oxisols and on growth of two high biomass production-grasses (Brachiaria decumbens and Panicum maximum) that were evaluated for their Cd phytoextraction potential. We also assessed how these interactions could influence the availability of Cd and its possible phytoextraction by these grasses. The Cd fraction bound to carbonates was higher in the winter conditions, while Cd bound to Fe- and Mn oxides was higher in the summer conditions, which resulted in a higher Cd availability in winter compared to summer conditions. B. decumbens and P. maximum took up more Cd when grown in the winter conditions, but their biomasses were not affected by the higher Cd uptake. The occurrence and relative abundance of bacterial taxa in the bare soil differed from the soils cultivated with grasses, where the Gammaproteobacteria predominated. However, no positive correlations were observed between the rhizosphere bacterial community in the cultivated soils and Cd availability, irrespective of the season conditions.