Effects of different restoration years on soil carbon sequestration and water retention capacity in bamboo forest: A case study in Southwest China Karst

The Grain for Green Program (GGP) is an ecological protection plan launched by China. In this context, much cultivated land in Southwest China Karst has been converted into bamboo forest to balance both ecological and economic benefits. This study selected typical areas in southern Sichuan Province and used natural bamboo forests (CK) as controls to analyze the changes in soil carbon sequestration and water retention capacity of bamboo forests with different restoration periods. The results showed that there was no significant change in soil mechanical composition during forest restoration. The soil bulk density (BD) showed a decreasing trend overall with the restoration period. The total porosity (P_t) and capillary porosity (P_c) showed a trend of first decreasing and then increasing with the increase of restoration years, while no obvious change pattern was found in non-capillary porosity (P_o). The variation characteristics of water retention capacity are similar to porosity, and returning farmland for 5 years can achieve good water retention performance, even higher than CK. The total organic carbon (TOC) and labile organic carbon (LOC) in the soil of bamboo forests after 20 years of returning farmland were significantly higher than those in 5 and 10 years of bamboo forests, and their organic carbon content was close to that of CK. It is worth noting that the soil organic carbon activity reached its optimal state after 10 years of returning farmland. To sum up, the implementation of the project of returning farmland to bamboo can effectively improve the soil carbon sequestration and water retention capacity. The research results provide a scientific basis for the optimization of the measures of the GGP, and help to promote the sustainable development in Southwest China Karst.