Effects of Warming on Soil Biogeochemistry at Harvard Forest 2014-2015

More than two decades of experimental soil warming in the Prospect Hill tract of the Harvard Forest has revealed non-linear soil respiration (HF005) and soil carbon loss patterns (Melillo et al., Science, 2017). The datasets here were collected to evaluate how the quantity and quality of soil carbon has been affected by 5C warming, and to assess the role that altered extracellular enzyme allocation may play in this. We collected soils over the 2014 growing season, after 23 years of soil warming. We confirmed previous results that warming had depleted the soil of organic matter, and this was accompanied by an overall decrease in microbial biomass particularly apparent in the forest floor in the fall. Using pyrolysis-GCMS, we found that the relative abundance of soil organic matter compound classes was unaffected by warming in the upper organic horizon (“forest floor”). However, lipids increased in relative abundance to the detriment of polysaccharides and lignin in the upper mineral soil, where warming had depleted soil mineral surfaces of organic matter. Despite these changes in soil organic matter quantity and quality, the potential extracellular enzyme activity per gram of soil was unaffected by warming treatment under common lab conditions. However, under in-situ temperature conditions, warming increased enzyme activity per unit microbial biomass, indicating heated plot microbes get better return on their enzyme investment than those in control plots.