The competitive vs. complementary bacteria‐fungi interactions promote microbial release of Fe(III)‐fixed phosphorus: the roles of exogenous C application

Abstract

The phosphorus deficiency is very common in Fe(III)-rich soil, and one of the key point is to clarify the condition in release or desorption of phosphorus from the Fe(III)-rich minerals. The present study was to explore the effect of labile carbon on microbial reduction of Fe(III) and release of phosphorus in root-free sub-tropical soil. A two-compartment microcosm was collected, in which the roots of Medicago sativa L. cultivar 'Aohan' were confined within one compartment by a barrier of 30-μm nylon mesh, while mycorrhizal hyphae could penetrate to the second compartment. Arbuscular mycorrhizal fungi (Funelliformis mosseae) were added to the root compartment and iron-reducing bacteria (Klebsiella pneumoniae) were added to the hyphal compartment. Hyphal compartments were provided with two levels of additional carbon (0 and 23 mg C kg -1 soil as sodium acetate) and eight levels of inorganic phosphorus (0 to 35 mg P kg -1 soil as KH 2 PO 4 ). At low phosphorus levels (< 5 mg P kg -1 soil), shoot biomass, and total biomass phosphorus were substantially less with added carbon in the presence of iron-reducing bacteria. Carbon had little effect without iron-reducing bacteria. At higher phosphorus levels (> 15 mg P kg -1 soil), the effect of added carbon was reversed; that is shoot biomass and total biomass phosphorus were greater with added carbon. Available soil phosphorus showed a similar response to added carbon-less at low levels of phosphorus and greater at higher levels of phosphorus. Microbial phosphorus in the presence of iron-reducing bacteria was always higher with added carbon at all corresponding levels of soil phosphorus. Taken together, these results show that some phosphorus mobilized by iron-reducing bacteria was converted into microbiological phosphorus, but there was an obligatory requirement for labile carbon for this to happen-reducing the amount of phosphorus that was absorbed by the mycorrhizal hyphae. Iron-reducing bacteria and mycorrhizae showed a competitive interaction at lower levels of available soil phosphorus, and a complementary, or possibly a carbon-dependent synergistic function at higher levels of available phosphorus. These results demonstrate that phosphorus released from ferralsols by iron-reducing bacteria is positively mediated by both phosphorus and labile carbon and, hence, that phosphorus release and mobilization by iron-reducing bacteria is likely to be enhanced by additions of exogenous carbon.

Enhancing phosphorus bioavailability in lateritic red soil: Combining Bacillus subtilis inoculated microbial organic fertilizer with reduced chemical input

“…Several studies have reported that the addition of organic or bio‐organic fertilizers can alter P‐solubilizing bacteria or iron‐reducing bacteria community structure. Moreover, organic or bio‐organic fertilizers can promote the conversion of Fe/Al‐bound P fractions by significantly increasing the activities of soil dehydrogenase, alkaline phosphatase and acid phosphatase enzymes and significantly decreasing Fe oxide activities following treatment with bio‐organic fertilizer, including P‐solubilizing bacteria, in red soil (Etesami et al., 2021; Rawat et al., 2022; Zhang & Ding, 2018). NBW is a bio‐organic fertilizer inoculated with B. subtilis ; which could release organic acids to mobilize the P and participate in the release of Fe/Al‐P (Saeid et al., 2018).…”