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Harvard Forest Symposium Abstract 2014

  • Title: Twenty years of experimental soil warming has increased the diversity of microbes associated with recalcitrant carbon decomposition
  • Primary Author: Grace Pold (University of Massachusetts Amherst)
  • Additional Authors: Kristen DeAngelis (University of Massachusetts Amherst); Jerry Melillo (Marine Biological Laboratory)
  • Abstract:

    Microbes play vital roles in many aspects of global carbon cycling, not least of which is the respiration and stabilization of soil organic matter. Climate change is expected to change these processes, but exactly how is still uncertain. After twenty years of experimental warming at the Harvard Forest's Prospect Hill tract, the depth of the carbon-rich organic horizon has shrunk by a third. Furthermore, the bacterial community is more diverse and has begun to resemble that of the carbon-poor mineral horizon. Despite an apparent loss of much of the more-easily degraded components of soil organic matter, fungi, typically thought of as the dominant decomposers of recalcitrant soil carbon, have decreased in abundance, while bacteria have increased. Carbon dioxide flux from the soil remains high. Together, these results indicate that warming may have opened new niches for bacteria capable of recalcitrant C decomposition.

    To evaluate the hypothesis that warming has increased the diversity of microbes capable of degrading recalcitrant carbon such as lignin, we buried BioSep beads amended with the complex heteropolymer lignin in the Prospect Hill experimental warmed and control sites. After 11 weeks, the beads were recovered and bacterial communities analyzed by sequencing the 16S ribosomal RNA genes. Warming increased the richness, evenness, and phylogenetic diversity of bacteria associated with lignin beads. This method also identified key, highly-abundant organisms that responded strongly to warming. In particular, while members of the Alphaproteobacteria order Rhizobiales showed large, but mixed responses to elevated temperature, members of the phylum Actinobacteria showed smaller but more consistent increases in relative abundance.

    Together, these results support the possibility that warming has opened new niches for recalcitrant carbon decomposers in the soil. We have isolated a number of the most abundant bacteria from this site, and are now trying to link shifts in community structure with shifts in ecosystem function by assessing the ability of these organisms to decompose the different components of soil organic matter.

  • Research Category: Large Experiments and Permanent Plot Studies, Soil Carbon and Nitrogen Dynamics