Effects of afforestation on soil CH4 and N2O fluxes in a nsubtropical karst landscape

Abstract

Afforestation is of importance for terrestrial carbon sequestration as well as soil and water conservation in karst landscapes. However, few studies have evaluated the effects of afforestation on soil CH4 and N2O emissions in subtropical karst areas. Thus, a year-round field experiment was conducted to quantify the effects of afforestation on soil CH4 and N2O fluxes from a subtropical karst landscape in South China. In this study, soil CH4 and N2O fluxes were simultaneously monitored using static chamber-gas chromatography from three paired sites, including a cropland site (SC) and adjacent sites at two stages of afforestation, a shrubland (SD) and a woodland (AF). The results showed that annual soil CH4 uptake for SC, SD, and AF sites were 1.53 ± 0.20 kg C ha−1 yr−1, 2.90 ± 0.20 kg C ha−1 yr−1, and 5.68 ± 0.18 kg C ha−1 yr−1, respectively. Afforestation (i.e., SD and AF sites) significantly increased soil CH4 uptake compared with the adjacent cropland. Annual soil N2O fluxes for SC, SD, and AF sites were 2.38 ± 0.17 kg N ha−1 yr−1, 0.94 ± 0.14 kg N ha−1 yr−1, and 0.47 ± 0.01 kg N ha−1 yr−1, respectively. Afforestation significantly decreased soil N2O fluxes compared with the adjacent cropland. The effects of afforestation on soil CH4 and N2O fluxes in the present study were mainly attributed to changes in soil characteristics, such as temperature and moisture, as these were significantly correlated with soil CH4 and N2O fluxes across different experimental sites. The present study highlights that afforestation is an effective land use management practice to mitigate non-CO2 greenhouse gas emissions from subtropical karst landscapes in South China.