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Harvard Forest Symposium Abstract 2016
- Title: Results from a long-term experiment implicates both direct and indirect effects of warming on forest soil carbon loss
- Primary Author: Grace Pold (University of Massachusetts - Amherst )
- Additional Authors: Kristen DeAngelis (University of Massachusetts Amherst); Stuart Grandy (University of New Hampshire - Main Campus); Jerry Melillo (Marine Biological Laboratory)
- Abstract:
As earth's climate continues to warm, it is vital to understand how the capacity of terrestrial ecosystems to retain carbon will be affected. At a decadesÂlong soil warming experiment in central Massachusetts, soil respiration has shown a triphasic pattern, increasing with the onset of warming, decreasing after a decade only to increase again a number of years later. This secondary increase in soil respiration occurred despite evidence for depleted soil organic matter carbon pools, and concurrent with changes in the structure of microbial communities. Here we set out to assess the hypothesis that warming has increased microbial access to remaining soil organic matter via increased extracellular enzyme activity and/or reduced physical protection. Microbial biomass, soil respiration, and potential activities of enzymes for litter decomposition were measured six times throughout the growing season, while changes in the isotopic ratio and physical structure of soil organic matter pools were assessed in mid summer. Both the forest floor (organic horizon) and the upper mineral horizon were sampled.
Soil carbon stocks were smaller and relatively depleted of biopolymers characteristic of plant litter in the mineral horizon, while total microbial biomass was lower in the organic horizon. Potential extracellular enzyme activity was generally unaffected by warming treatment, although activity per unit microbial biomass at in-Âsitu temperatures was higher. We failed to find evidence for reduced physical protection of soil organic matter, as the physical location of soil organic matter in the upper mineral horizon between heated and control plots did not differ. These results indicate that chronic warming has depleted the soil of organic matter, selecting for a smaller, more active community. Future work is necessary to determine whether these heated plot communities are processing more compounds characteristic of later stage soil organic matter decomposition. - Research Category: Forest-Atmosphere Exchange
Large Experiments and Permanent Plot Studies
Soil Carbon and Nitrogen Dynamics
