Two decades of warming increases diversity of a potentially lignolytic bacterial community.

Grace Pold,Jerry M Melillo,Kristen M Deangelis

doi:10.3389/fmicb.2015.00480

Grace Pold, Jerry M Melillo + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2015.00480

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Abstract

As Earth's climate warms, the massive stores of carbon found in soil are predicted to become depleted, and leave behind a smaller carbon pool that is less accessible to microbes. At a long-term forest soil-warming experiment in central Massachusetts, soil respiration and bacterial diversity have increased, while fungal biomass and microbially-accessible soil carbon have decreased. Here, we evaluate how warming has affected the microbial community's capability to degrade chemically-complex soil carbon using lignin-amended BioSep beads. We profiled the bacterial and fungal communities using PCR-based methods and completed extracellular enzyme assays as a proxy for potential community function. We found that lignin-amended beads selected for a distinct community containing bacterial taxa closely related to known lignin degraders, as well as members of many genera not previously noted as capable of degrading lignin. Warming tended to drive bacterial community structure more strongly in the lignin beads, while the effect on the fungal community was limited to unamended beads. Of those bacterial operational taxonomic units (OTUs) enriched by the warming treatment, many were enriched uniquely on lignin-amended beads. These taxa may be contributing to enhanced soil respiration under warming despite reduced readily available C availability. In aggregate, these results suggest that there is genetic potential for chemically complex soil carbon degradation that may lead to extended elevated soil respiration with long-term warming.

Highlights

The size of the soil carbon pool exceeds that of atmospheric and terrestrial vegetation carbon pools combined (Jobbágy and Jackson, 2000), making the fate of soil carbon a key variable in global climate models (McGuire et al, 2001; Wieder et al, 2013)
Overall, unamended beads had a greater fraction of reads assigned to genera with known lignin-degraders than lignin-amended beads did, but this was heavily skewed by Burkholderia, which accounted for almost 70% of the operational taxonomic units (OTUs)
We found evidence for a change in the structure of the bacterial community adapted to degradation of a major litter component, lignin, as we have seen for the “whole-soil” bacterial community after two decades of warming at this site (DeAngelis et al, 2015)

Summary

Introduction

The size of the soil carbon pool exceeds that of atmospheric and terrestrial vegetation carbon pools combined (Jobbágy and Jackson, 2000), making the fate of soil carbon a key variable in global climate models (McGuire et al, 2001; Wieder et al, 2013). In order to access polymeric carbon outside the cell, soil microorganisms produce extracellular enzymes that are affiliated with cell membrane surfaces or extracellular polysaccharides, or that are released into the environment (Wallenstein et al, 2011). These extracellular enzymes may have thermal optima greater than the temperatures they experience in the soil (Parham and Deng, 2000; Yan et al, 2010; Schipper et al, 2014), such that moderately elevated temperatures favor increased activity, as predicted by the Arrhenius equation (Stone et al, 2012; Baldrian et al, 2013). Substrates that were previously degraded at relatively low rates due to the high activation energy of the decomposition reaction may be more readily degraded, it is unclear if this holds for soil enzymes (Davidson and Janssens, 2006; Baldrian et al, 2013; Erhagen et al, 2015)

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