Disentangling the role of soil bacterial diversity in phosphorus transformation in the maize rhizosphere

Here, we hypothesized that there is a positive correlation between the soil bacterial diversity and the availability of phosphorus (P) from less soluble (organic calcium phytate and Araxá rock phosphate) or soluble (triple superphosphate) source under maize cultivation in a mesocosm experiment. This hypothesis was evaluated over a gradient of soil bacterial diversity (estimated by the Shannon index) generated by the dilution-to-extinction methodology (from 10−1 to 10−9). The experiment was conducted in a greenhouse for 30 days, followed by analyses of plant characteristics (dry weight, root and shoot measurements, and leaf and root P contents) and bacterial community diversity and activity (community structure, composition, and abundance, plus enzymatic activity) in bulk and rhizospheric soils. The bacterial diversity index negatively correlated with the labile P fraction in the soil and the P content in maize. However, enrichment of P-mineralizing microorganisms (based on the abundance of the phoD gene) was detected at higher microbial dilutions (10−9). The enrichment of some bacterial groups specialized in P conversion (e.g., Chitinophagaceae) in biomass could limit P availability in the soil and the rhizosphere resulting in possible competition with plants to acquire P and convert it into biomass instead of promoting plant growth. Therefore, the reduction in bacterial diversity could result in an imbalance in microbial interactions promoted by the enrichment of specific groups compromising plant development. The results indicate that a better understanding of the microbial community associated with P cycling is critical for better use of P in sustainable agriculture.