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Harvard Forest Symposium Abstract 2010

  • Title: Diel Patterns of Autotrophic and Heterotrophic Respiration: Links to Phenology
  • Primary Author: Kathleen Savage (Woods Hole Research Center)
  • Additional Authors: Eric Davidson (University of Maryland - Center for Environmental Science); Jim Tang (Marine Biological Laboratory)
  • Abstract:

    Soil respiration (Sr) is an aggregation of two belowground processes, autotrophic (live root and mycorrhizal fungal symbionts: Rr) and heterotrophic (live microbial decomposition of soil organic matter: Rm) respiration. Sr is often measured and modeled as a single process, however Rm and Rr typically originate from a variety of species and may respond differently to temperature, soil water content and substrate availability at diel and seasonal time scales. Automated respiration chambers were utilized in conjunction with the trenching method to examine the links of Rr to phenology at diel time scales.

    At the Little Prospect Hill tract at Harvard forest, we used the trenching method to partition Sr into its components. In the late fall of 2008 (DOY311), a trench was dug (to 1m depth) around a 5x5m area, severing all roots leading into the treatment plot. Plastic tarp was placed along the walls of the trench and then backfilled. Three automated Sr chambers were place in each of the trenched and un-trenched plots. The measured fluxes from the trenched plot represent the microbial component, Rm, of Sr, and the non trenched control plot the combined microbial and root respiration components, Sr. The difference (Sr-Rm) represents the root respiration component, Rr.

    The seasonal diel pattern of Sr and Rm vary with the control plot Sr peaking later in the evening (2000hrs) and Rm peaking earlier in the day (1730hrs), Figure 1. Peak Rr, occurred around 2200 hrs, much later than either peak air temperature, soil temperature and PAR (Figure 1), indicating that Rr is decoupled from soil temperature and related to other factors, such as aboveground processes.

    Looking at the diel pattern during differing phenological stages (Table 1) the mean daily respiration (yo) of Sr was significantly greater than Rm at all seasonal stages. The diel amplitude(A) of Sr was significantly greater than that of Rm from late spring through to late fall. During the most active portion of the growing season (late spring-fall) the peak time for Sr occurred later in the day than Rm.

    The difference in peak timing of Sr and Rm during the most active portion of the growing season is further indication that the Rr component of Sr, which peaks later in the day than Rm and is decoupled from soil temperature, is significant enough in its contribution to Sr that it can alter the diel pattern of Sr when trees are most active.

  • Research Category: Forest-Atmosphere Exchange

  • Figures:
  • C:DataDataAnalysisReportsharvard forest symposium absFigure1 2010 abs.pdf
    C:DataDataAnalysisReportsharvard forest symposium absTable 1 2010 abs.pdf