Iron‐reducing bacteria can enhance the activation and turnover of the Fe(III)‐fixed phosphorus for mycorrhizal plants

Abstract

In a greenhouse experiment, Medicago sativa was grown in iron‐rich soil colonized with iron‐reducing bacteria (IRB) and/or Glomus mosseae (GM) under different inorganic phosphorus levels, which was to understand the effects of IRB and GM on the activation and turnover of the Fe(III)‐fixed phosphorus. The results showed that at the both P rates, dual‐inoculation treatment stimulated the hyphal growth and increased the shoot P content. IRB could accelerate mycorrhizal colonization, and showed a positive effect on plant biomass and P uptake at both P levels. Compared to sole‐IRB or GM treatment, the dual inoculation treatment increased the soil available P content at both P rates (p < 0.05), which was in the following order: the dual IRB+GM > the sole IRB > the sole GM > control for soil SMP content at low P rate, whilst the dual IRB+GM > the sole IRB ≈ the sole GM > control treatment at high P rate. Compared with the IRB treatment, the GM treatment significantly decreased the soil available P content and the MBP content at low P rate, but made no difference at high P rates. The soil MBC in dual‐inoculation treatment was greatest under the high P level, while the highest soil MBC was the sole‐GM treatment under the low P level. The sole GM treatment showed significantly (p < 0.05) higher soil MBC than that of sole IRB at low P rate (p < 0.05), while there was no significant differences between sole IRB and sole GM at high P rate. Our results suggested that the interaction between GM and IRB had synergetic effect on the mobilization of Fe(III)‐fixed P and their relationship could be regulated by the turnover of MBP. The fact that plants acquired more P via mycorrhizal pathway in the GM‐IRB system suggested that the three symbiont of plant‐GM‐IRB had great ecological and functional significance for P activity in tropical and subtropical soil.

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

“…Microorganisms interact in the soil both synergistically and antagonistically to influence the development of colonization and resource competition and acquisition ( Artursson et al, ; Arriagada et al, ; Tanwar et al, ). Previously, we have shown that interactions between IRB and AMF had a positive effect on the infection rate and root colonization of AMF ( Zhang et al., ). It has also shown previously that the contribution of mycorrhizae to plant P uptake may be the greatest under intermediate levels of available P levels, with both low and high levels of P appearing to depress mycorrhizal function ( Chu et al, ).…”

“…Soil microorganisms are the key drivers in soil functional processes ( Cleveland et al., ; Zhang et al, ), such as soil carbon cycling, release and turnover of nutrients, particularly P for subsequent plant capture ( Carney and Matson , ; Van der Heijden et al, ). The releasing of Fe‐P is closely linked to the C‐dependent redox processes of Fe oxide by IRB ( Zhang et al., ). As a biogeochemical redox agent, IRB can increase the mineralization of soil organic matter and enhance the nutrient availability, especially P from Fe‐P in subtropical soils ( Chacón et al, ).…”

“…a). Labile C accelerates the reduction of Fe(III) to ferrous compounds and the mobilization of P, increasing the P‐sorption capacity of the soil ( Liptzin and Silver , ; Zhang et al., ). Although P mobilization was increased, the rate of P release may be underestimated because some of the mobilized P was simultaneous re‐adsorbed on Fe surfaces ( Camargo et al, ).…”

“…We previously found that the P release was improved in the presence of both iron‐reducing bacteria and AMF. However, in this case, C embodied in microbial biomass seemed unable to provide the C required for the redox reactions of IRB under low P availability ( Zhang et al, ). It is proposed that additional labile C could stimulate the rates of Fe(III) reduction with IRB for the mobilization of phosphate associated with Fe(II/III) minerals ( Chacón et al, ; Liptzin and Silver , ), which subsequently promote the absorption of P by AMF and transferring to the host plants ( Minaxi et al, ).…”

“…The concept of the biological transformation or turnover of Fe‐P has been proposed for a long time ( Tare , ; Oberson et al, ; Liptzin and Silver , ). Mycorrhizal plants must, however, compete with other soil microorganisms for available P in processes influenced by the ratio of soil organic C and available P ( Marschner , ; Zhang et al, ). Understanding the interactions between AMF and IRB may give insight into manipulating specific microorganisms in P nutrient turnover and plant uptake to understand integrated below‐aboveground links and ecosystem functioning ( Richardson and Simpson , ; Minaxi et al, ).…”