Monday, November 13, 2006
92-10

Heterotrophic and autotrophic contributions to the del-13C signature of soil respiration at high and low moisture levels.

Claire Phillips1, Zachary Kayler2, Barbara Bond1, Christian Andersen3, and Paul Rygiewicz4. (1) Dept of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, (2) Oregon State University, Dept. Forest Science, Corvallis, OR 97331, (3) Environmental Protection Agency, Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97331, (4) Environmental Protection Agency, Western Ecology Divison, 200 S.W. 35th Street, Corvallis, OR 97331

    The carbon isotopic signature of soil respiration has been demonstrated to be closely linked to the signature of recent photosynthate, suggesting autotrophs and autotroph-dependent organisms hve a large influence on soil CO2 flux. Under low soil moisture, both plant phloem and soil respired CO2 become enriched in 13C. However, it has not been demonstrated that the change in the isotopic signature of soil respiration under low moisture is due entirely to autotrophs. For example, it is not known whether the microbial component of soil respiration also becomes enriched with 13C with declining soil moisture.  It has also not been demonstrated how the relative contributions of autotrophic and heterotrophic respiration change as a proportion of total soil respiration as moisture declines.  To learn more about moisture effects on the isotopic composition of soil respiration, we tested the following two hypotheses: 1) heterotrophic respiration does not change carbon isotope composition under high and low moisture conditions, and 2) autotrophic respiration rates are more sensitive to soil moisture than heterotrophic respiration rates and will constitute a smaller proportion of total soil respiration under low moisture as compared with high moisture conditions.