Soil organic carbon stocks and soil respiration in tropical secondary forests in southern Mexico

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The soil CO2 efflux is recognized as one of the largest fluxes in the global carbon cycle, and small changes in the magnitude of soil respiration could have a large consequence on the concentration of CO2 in the atmosphere. In this study, we analyzed the soil organic carbon (SOC) stocks and CO2 efflux from soil respiration in a tropical secondary forest succession grown after abandonment of swidden agriculture in Southern Mexico. The study was conducted in a chronosequence of semi-evergreen tropical secondary and primary forests in the southern part of Yucatan Peninsula, Mexico. We collected soil samples (up to 30 cm depth) from 32 carbon monitoring plots and analyzed these for physical and chemical soil properties. Soil respiration measurements were carried out by using PP systems EGM-4 (an infrared gas analyzer). Analysis of variance (ANOVA), correlation, and regression was performed to test differences between forest age groups as the independent variable and soil respiration, organic as well as inorganic carbon in soil. Contrary to the hypothesis, SOC in the mineral soil horizon did not increase with forest age. Soil CO2 efflux did not correlate to soil organic carbon, it rather correlated to carbonate concentration in the soil. Higher CO2 efflux in carbonate rich soils can be explained probably by the faster decomposition but the slower ultimate mixing of organic matter in mineral soils of carbonate origin. However, it needs further investigation in separating soil CO2 efflux into autotrophic, heterotrophic, and abiotic fluxes to better understand the role of carbonate soils in atmospheric CO2 exchange. eng

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