Discrete taxa of saprotrophic fungi respire different ages of carbon from Antarctic soils

Kevin K Newsham,Filipa Cox,Clare H Robinson,Mark H Garnett

doi:10.1038/s41598-018-25877-9

Kevin K Newsham, Filipa Cox + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-25877-9

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Abstract

Different organic compounds have distinct residence times in soil and are degraded by specific taxa of saprotrophic fungi. It hence follows that specific fungal taxa should respire carbon of different ages from these compounds to the atmosphere. Here, we test whether this is the case by radiocarbon (14C) dating CO2 evolved from two gamma radiation-sterilised maritime Antarctic soils inoculated with pure single cultures of four fungi. We show that a member of the Helotiales, which accounted for 41–56% of all fungal sequences in the two soils, respired soil carbon that was aged up to 1,200 years BP and which was 350–400 years older than that respired by the other three taxa. Analyses of the enzyme profile of the Helotialean fungus and the fluxes and δ13C values of CO2 that it evolved suggested that its release of old carbon from soil was associated with efficient cellulose decomposition. Our findings support suggestions that increases in the ages of carbon respired from warmed soils may be caused by changes to the abundances or activities of discrete taxa of microbes, and indicate that the loss of old carbon from soils is driven by specific fungal taxa.

Highlights

The mass of organic carbon in soils is estimated to be two to three times that of the carbon which is present in gases in the Earth’s atmosphere[1]
Studies using selective microbial inhibitors consistently indicate that the CO2 derived from the fungal catabolism of organic compounds dominates the carbon evolved from soils, with the mean percentage contributions of fungi and bacteria to soil respiration ranging from 60:40–70:30 respectively in arable, grassland and forest soils and litters[9]
Blastn searches in the UNITE database indicated that ribosomal DNA internal transcribed spacer (ITS) regions of two fungi isolated from washed roots of D. antarctica sampled from Signy Island and Léonie Island in the maritime Antarctic (Fig. 1) matched closely with members of the order Helotiales (Table 1)

Summary

Introduction

The mass of organic carbon in soils is estimated to be two to three times that of the carbon which is present in gases (principally CO2) in the Earth’s atmosphere[1]. The complex organic polymer lignin is typically decomposed by members of the phylum Basidiomycota, which frequently synthesize lignin modifying enzymes, with cellulose being broken down by a wider range of fungi, typically those belonging to the Basidiomycota and Ascomycota[10,11,12]. Fungi such as Mucor and Mortierella spp., previously placed in the Phycomycetes but in the Mucoromycotina, usually have more restricted enzyme profiles, and tend to decompose simpler organic compounds such as sugars[12]. By measuring fungal enzyme activities and the δ13C content and efflux of CO2 respired from soil, we inferred which soil organic compounds are targeted by each fungal taxon

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