The effect of experimental warming on soil respiration in two mixed deciduous forests

Background/Question/Methods

Exchange of carbon dioxide from soils to the atmosphere is one of the largest fluxes in the global carbon cycle and is significantly higher than the release of carbon dioxide from anthropogenic activities. Warming trends associated with climate change have the potential to increase this flux, thus affecting the carbon storage capacity of the terrestrial biosphere. Ultimately this could lead to a positive feedback that would exacerbate projected warming trends. Previous climate warming studies have all been conducted on nutrient rich soils with relatively abundant organic matter, and not on low-organic matter ancient clay Ultisol and Oxisol soils that typify much of the lower-latitude zones of the world (ie; southeastern U.S. Piedmont, subtropics and tropics). Therefore, the goal of this experiment was to determine the effect soil warming has on in situ soil respiration at two mid-successional oak forests, Duke Forest (North Carolina Piedmont) and Whitehall Forest (Georgia Piedmont). The experiment consists of 18.3m² open top chambers with two warming treatments (+3°C and +5°C above ambient) and two light conditions associated with closed forest canopies and in canopy gaps. Soil respiration measurements were taken monthly beginning in September 2010.

Results/Conclusions

At Whitehall Forest, Athens, GA, we observed no difference in soil respiration at either the pre-treatment time or after one-month warming. However, at Duke Forest we observed significant differences in soil respiration after one year of warming. The gap chambers exhibited a significant response to warming for the +3°C treatment, respiring 168% more than in the ambient chambers (p=0.04). Conversely, at +5°C gap treatment, there was no significant increase in respiration. In the forest treatments, there was a trend toward increasing respiration with an increase in warming. Initially, we believe warming depletes soil organic carbon through increased microbial respiration but may be constrained by a decrease in soil moisture as seen in high light (gap) and +5°C conditions.