D. Alex Gore
Variability of soil respiration among heterotrophic and autotrophic components
BSES Senior Research Project 2008

Abstract

Soil respiration is the process of CO2 loss from the soil (CO2 efflux) due to microbial decomposition of organic matter (heterotrophic) and plant root respiration (autotrophic). The components and driving forces behind soil respiration is vital to the understanding of the carbon cycle and global warming. CO2 efflux was measured at two sites in the Morgan Monroe State Forest, Indiana. The first site was undisturbed containing natural vegetation and detritus allowing heterotrophic and autotrophic respiration. The second site had all living plants removed and was trenched to prevent infiltrating roots allowing only heterotrophic respiration. The autotrophic component of soil respiration accounted for about 32% of total CO2 efflux. As litter composition was unaltered, soil temperature and soil moisture were the two most influential parameters affecting the dynamics of soil respiration (Figure 1).

Heterotrophic and Autotrophic site - A strong correlation to soil moisture was not found except at 0.5 g g-1 where increased soil moisture limited CO2 efflux in both sites. Soil respiration in both sites showed an exponential increase as temperature increased (Figure 2).

Heterotrophic respiration site - The untrenched site accounting for heterotrophic and autotrophic respiration shows a greater correlation to increasing temperature. The strong correlation to temperature of the untrenched site (blue points) indicates that the autotrophic component of soil respiration is significantly driven by temperature. The increase in soil respiration cannot be accounted for by increased microbial metabolism alone. An extensive study that separates heterotrophic and autotrophic responses to soil temperature and moisture will provide a better understanding of the carbon cycle within a forest ecosystem.