Mechanisms controlling soil respiration (CO2 and CH4) in southern peatlands
Production of soil gases is important in nutrient and carbon cycling, particularly in peatlands due to their large atmospheric emissions of several greenhouse gases. We examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall pocosins and gum swamps) which occur along a natural soil nutrient availability gradient. Short pocosins occur in the ombrotrophic center of the bog complexes and are extremely nutrient-deficient; tall pocosins are slightly less nutrient-deficient; and gum swamps are relatively nutrient-rich. Short pocosin had the lowest soil CO2 production rates under both aerobic and anaerobic conditions in laboratory experiments, while rates in tall pocosin were similar to or somewhat less than in the gum swamp. Methanogenesis rates were extremely low in laboratory experiments, and indicate that CH4 production is not a significant pathway of carbon flow in these peatlands. Methane production is also low in relation to other peatlands. Amendment experiments indicate that the poor substrate quality of the highly decomposed, humified peat limits both CO2 and CH4 production rates, even though the peat is 95% organic matter. Low soil nutrient concentrations and low pH do not directly limit soil respiration in these peatlands, although there is a positive feedback of nutrients with organic matter inputs and litter quality, causing greater soil respiration in nutrient-rich sites. In situ CO2 emissions similarly differed between the communities, with highest rates in the gum swamp and lowest rates in the pocosins. Emissions were highly seasonal with soil temperature explaining the majority of the temporal variability. Maximum potential CH4 emission estimates derived from laboratory temperature relationships and in situ soil temperature data indicate that pocosins make an insignificant contribution to the global atmospheric CH4 flux. The continued existence of peatlands in warm climates may to a large extent depend on the low substrate quality of their soil organic matter, which maintains low decomposition rates under both aerobic and anaerobic conditions. © 1992.
Bridgham, SD; Richardson, CJ
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