Phosphate‐solubilising microorganisms for improved crop productivity: a critical assessment

Abstract

Summary Phosphate‐solubilising microorganisms (PSM) are often reported to have positive effects on crop productivity through enhanced phosphorus (P) nutrition. Our aim was to evaluate the validity of this concept. Most studies that report ‘positive effects’ of PSM on plant growth have been conducted under controlled conditions, whereas field experiments more frequently fail to demonstrate a positive response. Many studies have indicated that the mechanisms seen in vitro do not translate into improved crop P nutrition in complex soil–plant systems. Furthermore, associated mechanisms are often not rigorously assessed. We suggest that PSM do not mobilise sufficient P to change the crops’ nutritional environment under field conditions. The current concept, in which PSM solubilise P ‘for the plant’ should thus be revised. Although PSM have the capacity to solubilise P to meet their own needs, it is the turnover of the microbial biomass that subsequently provides P to plants over a longer time. Therefore, the existing concept of PSM function is unlikely to deliver a reliable strategy for increasing crop P nutrition. A further mechanistic understanding is needed to determine how P mobilisation by PSM as a component of the whole soil community can be manipulated to become more effective for plant P nutrition.

Roles of Phosphate Solubilizing Microorganisms from Managing Soil Phosphorus Deficiency to Mediating Biogeochemical P Cycle

“…However, the soil is a more diverse and spatially heterogeneous matrix than a growth medium, which will result in some of the discrepancies between the in vitro and in vivo potential of PSM to improve plant nutrition and growth [139]. The PSM-mediated bioavailable P is not utilized directly by plant or soil microbes; instead, it is quickly subject to precipitation or adsorption reactions in the immediate vicinity in which it is solubilized or desorbed by PSM [140]. Additionally, the P solubilization of exogenous PSM may be reduced due to the lack of persistence by competition with endogenous microbes for P resources, or by maladjustment of newly inoculated soil environment [141,142].…”

Plant-associated microbiomes promote nutrient turnover in impoverished substrates of a biodiversity hotspot

“…As root exudates are rich in organic compounds that recruit and sustain microbial communities [21], we hypothesized that Velloziaceae exudates fulfill a dual role: they increase the labile P concentration by direct solubilization and also recruit microorganisms that possess a complementary repertoire of molecular processes that increase P availability in the root’s vicinity. In this scenario, microorganisms would use phosphate for their own needs, but would benefit the system in the long term by mobilizing P otherwise unavailable to plants [29] (Figure 5A).…”

“…Investigation of the P turnover potential by Velloziaceae-associated microbiomes Microorganisms encode diverse mechanisms for P mobilization [28], and as their biomass turns over through time, P becomes available to plants [29] (Figure 5A). To investigate the P turnover potential of the V. epidendroides and B. macrantha microbiomes, we measured the total abundance of genes involved in environmental P mobilization (Suppl.…”

Review of Phosphite as a Plant Nutrient and Fungicide

“…While the mechanisms behind P solubilization by PSM are relatively well documented in vitro [44,45], less is known about potential PSM mediated oxidation of Phi to Pi. Raymond [46] provided an alternative perspective that although PSMs dominantly have the capacity to solubilize P to meet their own needs, it is the turnover of the microbial biomass that subsequently provides Pi to plants over a longer time. Thus, it likely will require substantial research to identify and quantify soil amendments that may facilitate microbial oxidation of Phi to Pi.…”