Fungi handling phosphorus: soil fungi ability to solubilise inorganic phosphate and mediate secondary minerals formation

Phosphorous (P) is both sequestered and mobilised in soil by biological and geochemical processes. However, it primarily tends to form insoluble complexes and minerals with calcium, aluminium, iron, and hydroxides, becoming consequently unavailable for plants. Soil microorganisms can increase the amount of bioavailable phosphorus through several biological processes as the acidification of their microenvironment, the mineralisation of organic phosphorus and the translocation of phosphates [1,2]. Saprotrophic fungi play critical geoactive roles in the P biogeochemical cycle. By leaching minerals and solubilising insoluble phosphorus, fungi determine the P concentration in the soil solution [2,3,4]. Moreover, fungal ability to store phosphorus in the biomass and pass it to plant roots may be pivotal in avoiding the loss of solubilised phosphorus. Phosphorus low mobility in soil is a limiting factor for productivity in most agricultural land. Because of the worldwide exhaustion of phosphorus mineral sources and the limited availability of fertilisers [5], the slow solubilisation of the mineral P already present in agricultural soils may be the key to ensuring sustainable and environmentally friendly crop production. This study aimed to evaluate, in vitro, the ability of 9 selected strains of soil fungi, with different life strategies, to solubilise, assimilate and store P from the insoluble tricalcium phosphate as its only source. Chemical analyses with SEM/EDX, colorimetric methods and ICP-MS were used to quantify the P released from TCP by the fungi and P concentration in the fungal biomass. We tested for each strain the ability to release P in a liquid culture medium, store it in their biomass and mediate its precipitation in secondary minerals. Tested fungi were able to solubilise tricalcium phosphate (TCP) to a different extent, increasing P concentration in a liquid medium and biomass and mediating new secondary minerals. References: [1] Alori E T et al. (2017) Front Microbiol 8:971 [2] Owen D et al. (2015) Appl Soil Ecol 86:41–54 [3] Shrivastava M et al. (2018) Springer ISBN 9789811300431 : 137–165 [4] Ceci A et al. (2018), Ambio 47:S30–S40 [5] White S and Cordell D (2017) Routledge ISBN 1-315-28161-9 : 59–72