Soil Carbon Dioxide Efflux in a Naturally Regenerated and a Planted Clear-Cut on the Virginia Piedmont
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Soils are a major component of the global carbon budget and may serve an important role in mitigating increasing atmospheric CO2 through their capacity to store carbon. In this regard, it is important to evaluate the implications of forest management on changes in carbon cycling and sequestration and to determine the magnitude by which the efflux of CO2 from the soil surface can vary in time and space. For this study, soil CO2 efflux was measured in 5 replicate blocks of naturally regenerated and planted loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), and eastern white pine (Pinus strobus) in a 50-acre clear-cut on the Virginia Piedmont. Rates of CO2 efflux were measured every 2 weeks immediately adjacent and away (1m) from newly planted seedlings and cut stumps using a dynamic, closed-chamber infrared gas analyzer system. For each measurement date, volumetric water content was taken in the top 17cm, using time domain reflectometry (TDR) and soil-surface temperature was recorded in the top 7cm, using a temperature probe. For the October measurement a 12cm depth soil core (7cm diameter) was collected for each location. Carbon, nitrogen, coarse fragments, roots, surface litter and coarse woody debris were measured separately for each core. Position (near and away from seedling) had a strong effect on soil CO2 efflux rates. For the first measurement date, rates were higher near the newly planted seedlings (3.09Î¼mol/m2/s) than those taken away from the seedlings (2.29 Î¼mol/m2/s).. The same trend was maintained for the CO2 efflux rates measured near a cut stumps (3.51Î¼mol/m2/s) and those taken away from the stump base (2.56Î¼mol/m2/s). Species proved to have no significant effect on respiration rates for any date and no interaction between species and position was observed. Regression analysis was used to model the influence of soil and plant factors on efflux rates. Temperature (29.2%), position (near and away from the seedlings and stumps base)* temperature, (7.7%), soil carbon (4.1%), organic matter (1.6%), and soil moisture (0.7%) proved to be the major drivers for soil respiration (R2 = 0.4329). When only data near seedlings or stumps were modeled, species had a significant effect on soil CO2 efflux rates. The largest seedlings, loblolly pine (100 cm3 seedling value), had on average the highest rates followed by shortleaf pine (30 cm3 seedling value) and eastern white pine, which were the smallest (9 cm3 seedling value). Stumps had the highest efflux rates. The mean soil respiration rate measured over a seven month sampling period was 2.58 Î¼mol/m2/s,, while the calculated carbon loss from the soil over the same period added up to 575 g C/ m2. The annual carbon loss was estimated to be 675 g C/ m2.
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