Phosphorus fertilization affects soybean rhizosphere phosphorus dynamics and the bacterial community in karst soils

Despite the high phosphorus (P)-mobilizing capacity of legumes, little is known about the dynamics of the P fractions and bacterial communities in the rhizosphere of legumes in karst soils. A field experiment was established to investigate P uptake, rhizosphere P fractions and bacterial community structure of soybean (Glycine max (L.) Merr.) in response to P fertilization (0 and 90 kg P ha−1) in karst soils. Significant rhizosphere acidification was observed during soybean cultivation. Phosphorus fertilization further decreased soil pH, HCl-Pi and residual P, but increased NaHCO3-Pi in the rhizosphere of soybean variety YC03–3, which was associated with the simultaneous increase in P uptake and biomass. In addition, the bacterial community composition was significantly altered by P fertilization through its effects on soil pH and Ca. Bacillales and Pseudomonadales were the primary taxa influencing P dynamics, especially in soils without P input. Nevertheless, P fertilization decreased the relative abundance of Bacillales and Pseudomonadales, probably due to the enhanced rhizosphere acidification and improved P status. In karst soils, recalcitrant P can be depleted directly or transformed into more labile fractions by soybean rhizosphere acidification, even when P fertilizer is applied. As a consequence, P fertilization suppressed the growth of bacteria (Bacillales and Pseudomonadales) that contribute to P mobilization due to the reduced demands on these taxa to release P. Our findings highlight the importance of P fertilization in chemical P mobilization, which may consequently influence biological P turnover in the soybean rhizosphere.