Effect of stand age on the temporal dynamics of soil active carbon and nitrogen in Chinese cypress artificial forests

Stand age is a key factor for reforestation, and it has an important influence on the sustainable development of artificial forests. In order to reveal the temporal dynamics of soil active carbon (C) and nitrogen (N) in Chinese cypress artificial forests (CAFs) under different stand ages, soil samples were collected from five stands (25, 35, 45, 55, and 65 years old) in rocky mountainous of North China. The characterization of soil active C and N components, like soil microbial biomass C (MBC), microbial biomass N (MBN), dissolved organic C (DOC), dissolved organic N (DON), ammonium-N (NH4+-N) and nitrate-N (NO3--N), as well as other soil properties were determined. The results showed that with the increase of stand age, the contents of soil MBC, MBN, DOC, DON, NH4+-N and NO3--N tended to increase first and then decrease, and most of them reached the highest values in 45 years old. Soil active C and N components all reached peak values in June, and all of them showed the most significant variations in 0 similar to 10 cm soil layer (P < 0.01). Correlation analysis revealed that soil active C and N components showed significantly positive correlations with soil total N, total C, the number of microorganism communities and soil water content, as well as litter biomass (P < 0.01). Stepwise multiple regression analysis demonstrated that soil total N was the key controlling factor to soil active C and N components. In conclusion, with the increase of stand ages, soil active C and N components of CAFs did not accumulate all the time, indicating that stand age should be regarded as an important factor for the sustainable management of artificial forests.