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

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.

Keywords: Bio-Sep beads; chemically complex carbon; climate change; in-situ enrichment; lignin degradation; microbial ecology; soil organic matter.

Figure 1

Effect of warming and soil on field-moist bead (A) and cell-normalized total oxidative enzyme activity (B). Shared letters indicates soil depth*warming treatment*lignin amendment effects are not significantly different at P = 0.05 using Tukey's HSD.

Figure 2

Principal coordinates plot of (A) UniFrac distances of bacterial communities and (B) Hellinger distance of Fungal communities. Lignin-amended and unamended beads support distinct communities, as demonstrated by the wide separation on the first axis.

Figure 3

Tree depicting OTUs which are significantly enriched in warmed (red branches) or control (blue branches) plots on lignin-amended BioSep beads. OTUs also affected by warming treatment in the unamended beads were excluded from the tree. Each branch is a single OTU. Outer ring denotes phylum or class.