[Characteristics of soil carbon, nitrogen, and water of Populus cathayana plantation along different vegetation restoration years in alpine sandy region].

As the most effective way to remedy and reconstruct the degraded ecosystems, vegetation restoration could affect soil carbon and nitrogen cycles and water balance. We examined the responses of carbon, nitrogen, and water in 0-200 cm soil layer to vegetation restoration years by analyzing their distribution characteristics across a restoration chronosequence of Populus cathayana plantation (5, 10, 15, 20, and 25 years) in alpine sandy region of the Qinghai-Tibetan Plateau. The results showed that the content and storage of soil organic carbon (SOC) and soil total nitrogen (STN) increased significantly, while that of soil inorganic carbon (SIC) decreased significantly with restoration years. SOC, SIC and STN content for the entire 200 cm soil layer were 0.41-1.24 g C·kg^-1, 4.53-8.07 g C·kg^-1, and 0.12-0.22 g N·kg^-1, respectively. SOC, SIC, and STN storage for the entire 200 cm were 16.08-33.51 t C·hm^-2, 187.12-241.02 t C·hm^-2, and 4.27-6.66 t N·hm^-2, respectively. After 25 years vegetation restoration, the storage of SOC and STN for the entire 200 cm soil layer were significantly increased by 68.1% and 39.6%, while the SIC storage was significantly decreased by 9.5% compared with the 5 years vegetation restoration. The storage of SOC, SIC and STN in the 100-200 cm soil layer were 1.3-1.4 times higher than those in the 0-100 cm layer. The storage of SIC within the 0-200 cm layer was 8.2 times of the SOC storage over the same layer. Compared with the 5 years restoration, SOC storage in the 0-200 cm soil layer of 10, 15, 20, and 25 restoration years increased by 13.3%-68.1%, which were 1.0-2.1 times of the STN storage, suggesting a decoupling of SOC and STN accumulation during restoration. After 15 years vegetation restoration, soil water content and storage peaked at 7.4% and 274.17 mm, respectively. Restoration years were significantly positively correlated with SOC and STN contents, but not related to water content. SOC, STN, and water storage were significantly and positively correlated with each other, resulting in a positive promoting effect between each pair. In conclusion, the inorganic carbon pool was a significant contributor to the total carbon pool in alpine sandy region of the Qinghai-Tibetan Pla-teau. Vegetation restoration year is a primary determinant of soil carbon, nitrogen, and water sequestration, with the contributions of deeper soil layers to regional levels being equally important and can not be ignored. This finding suggested that alpine sandy ecosystems required soil nitrogen input in the early vegetation restoration stages.