Will Secondary Vegetative Succession Reduce Carbon Dioxide Efflux From a Carolina Bay Histosol?.

North Carolina has over 600 000 ha of Histosols located in poorly drained areas along the lower Coastal Plain, in Carolina bays, and in pocosins.  Restoration of hydrology and native plant communities in agricultural fields occupying Histosols may result in net soil C sequestration and provide an economic incentive via C credit sales. Understanding of soil C dynamics as secondary succession proceeds is currently lacking for organic soils.  We hypothesized that average daily soil temperature will decrease with vegetative succession as canopy density and surface shading increase, leading to a net reduction in microbial respiration and CO₂ efflux, especially when hydrology is restored and soils become reduced.  A greenhouse experiment was designed to test the combined effects of soil moisture and surface shading on C loss from a Carolina bay organic soil material.  Intact cores (20-cm height × 20-cm diameter) were subjected to a water table (-15 cm) under three conditions of sunlight reduction: 0 (unshaded), 70, and 90% for 60 d. Thereafter, shading treatments were maintained for an additional 30 d with the water table removed.  The soil CO₂ efflux was measured periodically with a portable photosynthesis analyzer.  Soil redox potential was measured concurrent with CO₂ efflux and temperature was recorded hourly for the duration of the experiment.  Preliminary results indicate that there was no interaction (p = 0.58) between the two factors. The CO₂ efflux differed (p < 0.0001) among shading treatments (unshaded > 75% > 90%) and increased (p = 0.004) after the water table was removed.  Results suggest that soil C loss will decrease as secondary succession proceeds and hydrology is restored.  A field study is underway to observe CO₂ efflux from in-situ soil material under similar shade treatments.