Changes in soil organic carbon and total nitrogen stocks along a chronosequence of Caragana intermedia plantations in alpine sandy land

Accurate assessment of soil organic carbon (SOC) and total nitrogen (TN) stocks and analyzing the main influencing factors after revegetation for restoration of sandy soils in alpine regions are important for formulating sustainable management measures and understanding the role of revegetation in mitigating climate change. This study compared SOC and TN stocks and their vertical distributions among 6-, 11-, 17- and 31-year-old Caragana intermedia plantations and shifting sand dunes. The results showed that SOC and TN stocks significantly increased as plantation age increased, with the 31-year-old stands having the highest SOC stocks (26.73 Mg ha(-1)) and TN stocks (2.64 Mg ha(-1)), which were 97.4% and 149.56% higher, respectively, than those of the shifting sand dunes. Compared to the total soil depth, SOC and TN stocks at all stand ages were higher in surface soil (0-20 cm). SOC stocks in the surface soil of the 6-, 11-, 17- and 31-year-old stands were 38.03%, 71.32%, 103.67% and 253.30% higher, respectively, than those in the surface soil of the shifting sand dunes, and TN stocks in the surface soil were 17.03%, 117.96%, 148.93% and 232.06% higher, respectively, than those in the surface soil of the shifting sand dunes. The percentage of the SOC and TN stock in the 0-20 cm soil depth increased significantly as plantation age increased, with the 31-year-old plantation reaching 43.66% and 33.39%, respectively. Redundancy analysis and correlation analysis showed that at 0-20 cm soil depth, aboveground biomass was the main influencing factor for SOC and TN stocks. At 20-80 cm soil depth, fine root biomass and medium root biomass were the main influencing factors for SOC stocks, and medium root biomass was the main influencing factor for TN stocks.