Explaining temporal variations in soil respiration ratesand δ13C in coniferous forest ecosystems

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Daniel Comstedt has Master of Science (MSc) in Forestry from the Swedish University of Agricultural Sciences (SLU) in Umeå. The work of this Ph.D. was performed at the Department of Natural Sciences at Örebro University.

Soil respiration is a major fl ux of C in the terrestrial carbon cycle. Since a large part of the terrestrial C stock is stored in the soils of northern forest ecosystems, even small changes in soil respiration rates in these ecosystems could have an effect on atmospheric CO₂ concentrations. Soil respiration can be divided into autotrophic respiration (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic respiration (from decomposers of organic material). An important question is whether the two components of soil respiration respond differently to changing abiotic factors. In my thesis, in order to separate the two components, I used both manipulated and natural variations in δ13_{C as a marker for autotrophic respiration. The effect of elevated}

atmospheric CO₂ concentration and elevated temperature on soil respiration was studied in a whole tree chamber experiment conducted in a Norway spruce forest in northern Sweden. In another spruce forest, day-to-day variations of soil respiration rate and δ13_{C of soil respired CO}

2 were explained by above

and below ground abiotic conditions. Also, a trenching experiment was con-ducted in the latter forest. Elevated CO₂ concentration, while not elevated temperature, increased soil respiration rates, and δ13_{C data suggest the increase}

mostly resulted from autotrophic respiration. The day-to-day variations in soil respiration rate and δ13_{C seemed to be strongly linked to recent weather, with}

a shorter lag for soil respiration rate than for δ13_{C. However, the tightness of}

the link seemed to be dependent on good weather conditions up to a week before sampling. I concluded that that soil- and autotrophic respiration in N-limited forest ecosystems is to a large degree infl uenced by the availability of newly produced photoassimilates being transported to the roots and to a less degree dependent on temperature.

Örebro Studies in Biology 4 örebro 2008

Doctoral Dissertation

Explaining temporal variations in soil respiration rates

and δ

_{C in coniferous forest ecosystems}

Daniel Comstedt Biology