Pectin drives microbial phosphorus solubilization in soil: Evidence from isolation-based and community-scale approaches

A considerable part of soil phosphorus is bound to metal cations or metal oxides, and cannot be used in these forms by soil microbes and plants. Phosphate-solubilizing bacteria (PSB) are abundant in pectin-rich rhizosphere, and their pectin-degrading activity has been reported. Therefore, we hypothesized that pectin activates PSB and promotes soil phosphorus solubilization. To test this hypothesis, we first tested the phosphate-solubilizing activity of pectin-degrading bacteria. PSB were more frequently isolated from pectin-containing medium, compared with other media (P < 0.001). Further in a soil microcosm experiment, we examined whether pectin amendment accelerated soil phosphate solubilization. Pectin amendment decreased the concentrations of labile metallophosphate but increased the content of microbial biomass phosphorus in soils, meaning that phosphate solubilization was promoted by pectin amendment. In addition, PSB-like clades of bacteria increased by up to three times in response to pectin addition. This indicated that pectin amendment encouraged proliferation of PSB, accelerating soil phosphorus turnover processes initiated by solubilization of metallophosphate. In line with these results, genomic analysis indicated the widespread distribution of pectin-degrading genes among PSB, suggesting the possible co-evolution of pectin-degrading and phosphate solubilizing functions.