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Harvard Forest Symposium Abstract 2011
- Title: Autotrophic and Heterotrophic Contributions to Soil Respiration
- Primary Author: Kathleen Savage (Woods Hole Research Center)
- Additional Authors: Eric Davidson (University of Maryland - Center for Environmental Science); Sue Trumobre (University of California - Irvine)
- Abstract:
Soil respiration (Sr) is comprised of 2 components, autotrophic (live root and mycorrhizal fungal symbionts: Ra) and heterotrophic (microbial decomposition of soil organic matter: Rh) respiration. Since both are belowground processes, it is difficult to separate the relative contributions of each to Sr. The magnitude of the contribution of Rh and Ra to Sr may be dependent on tree species, soil characteristics and season, as well as climatic variables such as temperature and moisture. Several methods are available to examine the relative contribution of Ra and Rh to Sr: such as tree girdling and logging. The tree girdling process involves cutting through the tree bark (at breast height) to the xylem, which cuts the supple of photosynthate to the belowground roots, thereby removing the Ra component of Sr but leaving standing dead and little disturbance of the soils. Logging removes all tees of economically usable size from the location however slash piles are left in place and there is considerable disturbance to soils. Radio carbon dating was also used to partition Ra and Rh components of Sr in the control and girdled plots. The objective of this experiment is to look at the relative contribution of autotrophic (Ra) and heterotrophic (Rh) respiration to total soil respiration (Sr).
The experiment was a two block design, with 1 replicate of each treatment in each block. The first treatment was a girdling treatment and the second treatment was a logged treatment. Measurements of Sr were made using a vented, flow through, non-steady-state system at 6 collars randomly placed at each of the treatments (n=36). Sr was measured on a weekly to bi monthly basis from early spring to early fall between the hours of 9am to 3pm.
There was a decrease in Sr following girdling and logging attributed to the loss of the Ra component of Sr, but the pattern of loss differed between the two treatment types (Figure 1). Sr in the girdled plots did not show a decline in Sr until 2 years after girdling possibly due to roots utilizing stored carbohydrates and/or the increase in readily available carbon from recently killed root systems which supplied an increased Rh component. Sr in the logged plots decreased immediately following treatment, but began to increase in 2008-2009, likely due to an increase in shrubs present in those years, adding again to the Ra component of Sr. Table 1 shows the % gain (in positive-red) or loss of carbon (negative-black) from pre treatment to post treatment. By 2008 the girdled plots shows a 36% decrease in Sr. The logged plots showed as much as a 46% decrease in Sr in 2007. Radio carbon dating (Figure 2) suggests that about 43% of Sr is attributed to Ra and 57% attributed to Rh. The decrease in Sr in the girdled and logged treatment were at a maximum of 36% (girdled) and 46% (logged) suggesting that the Ra component estimated from both types of treatment experiments is similar to that estimated from the 14 C analysis (43%).
- Research Category: Forest-Atmosphere Exchange
- Figures: C:DataDataAnalysisReportsharvard forest symposium absHF abstract 2011 figures.pdf
