Characteristics of carbon sequestration and apparent stability of new sequestered carbon in forested torrid red soil at dry-hot valley
干热河谷林地燥红土固碳特征及“新固定”碳表观稳定性

Great concerns about potential for carbon (C) sequestration in forested soil and the stability of the sequestered C have been exerted under the background of global climate change. Organic C density in soil and in soil physical and biochemical fractions at various stages (1991, 1997, 2003 and 2010) in Acacia auriculiformis stand afforested in 1991 were investigated at Dry-Hot Valley via density fractionation and acid hydrolysis. The results showed that organic C density at surface (0-15 cm) and subsurface (15-30 cm) soil layers was 1.40 kg·m-2 and 0.99 kg·m-2 after 19 years of afforestation, respectively. The annual C sequestration rates of surface and subsurface soil layers were 37.89 g·(m2·a)-1 and 16.84 g·(m2·a)-1 during 1991-2010, respectively, and the sequestration was accelerating. The ratio of organic C in heavy fraction to in surface soil was 71.44% in 2003, which was significantly higher than that in 2010 (67.99%). The recalcitrant carbon index (IRC) in light fraction was significantly higher than that in heavy fraction at surface or subsurface layers in 2003, but both decreased with aging of plantation, especially IRC in light fraction. Approximately 57%-70% of new sequestered C was protected by physical mechanism and 33-49 percent was biochemical recalcitrant C during the stage from 12 to 19 years after afforestation. The results reveal that forested torrid red soil at Dry-Hot Valley may have a considerable capability of C sequestration. The biochemical stability of physically protected C is lower than the unprotected. Both the stability, however, decreases with the plantation age.