Functional Diversity of the Litter-Associated Fungi from an Oxalate-Carbonate Pathway Ecosystem in Madagascar.

Vincent Hervé,Pilar Junier,Finaritra Randevoson,Eric Verrecchia,Herintsitohaina Razakamanarivo,Anaële Simon,Guillaume Cailleau,Gabrielle Rajoelison,Saskia Bindschedler

doi:10.3390/microorganisms9050985

Abstract

The oxalate-carbonate pathway (OCP) is a biogeochemical process linking oxalate oxidation and carbonate precipitation. Currently, this pathway is described as a tripartite association involving oxalogenic plants, oxalogenic fungi, and oxalotrophic bacteria. While the OCP has recently received increasing interest given its potential for capturing carbon in soils, there are still many unknowns, especially regarding the taxonomic and functional diversity of the fungi involved in this pathway. To fill this gap, we described an active OCP site in Madagascar, under the influence of the oxalogenic tree Tamarindus indica, and isolated, identified, and characterized 50 fungal strains from the leaf litter. The fungal diversity encompassed three phyla, namely Mucoromycota, Ascomycota, and Basidiomycota, and 23 genera. Using various media, we further investigated their functional potential. Most of the fungal strains produced siderophores and presented proteolytic activities. The majority were also able to decompose cellulose and xylan, but only a few were able to solubilize inorganic phosphate. Regarding oxalate metabolism, several strains were able to produce calcium oxalate crystals while others decomposed calcium oxalate. These results challenge the current view of the OCP by indicating that fungi are both oxalate producers and degraders. Moreover, they strengthen the importance of the role of fungi in C, N, Ca, and Fe cycles.

Highlights

Microorganisms are essential drivers of plant material degradation and recycling in terrestrial ecosystems [1], and as such, they play key roles in numerous biogeochemical cycles
Several conditions are required to establish the existence of an active oxalate-carbonate pathway (OCP): the presence of both active oxalogenic and oxalotrophic organisms and a local increase in soil pH
Concerning the first element, T. indica is known to be an oxalogenic plant in which calcium oxalate crystals have been observed in secondary xylem [58] and bark compartment [59] of the tree

Summary

Introduction

Microorganisms are essential drivers of plant material degradation and recycling in terrestrial ecosystems [1], and as such, they play key roles in numerous biogeochemical cycles. The coupling between carbon and calcium cycles is well described in the hydro-atmosphere system [8] These two elements are intimately linked in terrestrial ecosystems, including forest soils [9,10,11], and microorganisms contribute to various processes and steps of these cycles [12,13,14,15]. This is, for instance, the case in the oxalate-carbonate pathway (OCP)

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