You are here

Harvard Forest >

Harvard Forest Symposium Abstract 2013

  • Title: How does soil carbon quality affect how fast soil microbes adapt to warming?
  • Primary Author: Grace Pold (University of Massachusetts Amherst)
  • Additional Authors: Kristen DeAngelis (University of Massachusetts Amherst)
  • Abstract:

    Background:



    The long-term warming experiments at the Harvard Forest provide a wealth of clues as to how the carbon cycle as a whole may respond to global warming in northeastern deciduous forests. Missing, however, is a mechanistic understanding of how the microbial communities which regulate soil carbon stability will respond. At the Prospect Hill warming site, elevated temperatures led to a burst of respiration, which is often seen in long-term warming experiments and attributed primarily to a reduction in soil carbon, and secondarily to microbial adaptation. However, despite a 10-15% reduction in soil carbon, respiration is elevated once again at this site, indicating that microbial adaptation may be more important for the long-term response of soil respiration to elevated temperatures than initially thought. Given that soils store more carbon than the atmosphere and terrestrial vegetation combined, understanding the factors which regulate the rate and extent of microbial adaptation to elevated temperatures is more important than ever.



    Hypothesis:



    We hypothesize that microbes adapt more rapidly to elevated temperatures under conditions of low-quality carbon availability than under conditions of high-quality carbon availability, because wastefulness with resources cannot be rewarded as well in the former as in the latter. We further hypothesize that changes in extracellular enzyme kinetics and shifts in community composition are important in this adaptation.



    Methods:



    To test this hypothesis, we are using artificial soils with either sugar maple (high quality) or oak leaf (low quality) litter as the sole carbon source. They are designed to mimic the texture and carbon content of a 50:50 mineral:organic soil taken from Prospect Hill. We will inoculate the soils with a microbial community extracted from Harvard Forest soils and incubate the soils at 4°C (the temperature at which the inoculant community was collected and has been stored) and 12°C, and assess carbon use efficiency at 12°C using “natural” carbon sources at eight time points over the course of eight months. Adaptation will be said to have occurred when the soil community incubated and assayed at 12°C has a higher carbon use efficiency than the equivalent soil incubated at 4°C and assayed at 12°C. At the end of the incubations, the Michealis Menten constant and temperature optimum will be assessed for two representative extracellular enzymes - N-acetylglucosaminidase and cellobiohydrolase, and changes in community composition will be evaluated using 16S rRNA sequences.



    Significance:



    First, this study will provide an improved understanding of how the ways that warming affects the chemical and community composition of plants also affects the response of microbial decomposers to soil warming. Second, this study will determine whether or not altered enzyme kinetics and community composition are important for soil microbes to adapt to elevated temperatures.

  • Research Category: Soil Carbon and Nitrogen Dynamics