北方农牧交错带温性盐碱化草地土壤碳组分对模拟增温的响应机制

中国北方农牧交错带温性盐碱化草地土壤有机碳库对全球气候变暖的响应趋势存在较大不确定性。作为温性盐碱性草地的典型分布区，山西右玉农牧交错带是探索相关研究的理想生境。基于山西农业大学野外观测研究站开顶式气室模拟增温实验平台，通过采集生长旺季土壤样品，探索温性盐碱化草地不同土层有机碳、氮组分对模拟增温的响应与适应机制。结果表明：(1)不同增温处理对土壤有机碳(C)、总氮(N)、颗粒性有机碳(POM-C)和氮(POM-N)、矿物结合态有机碳(MAOM-C)和氮(MAOM-N)、可溶性有机碳(DOC)和氮(DON),以及微生物量碳(MBC)和氮(MBN)等组分无显著影响，但显著降低了MAOM-C/MBC的比值；(2)除土壤可溶性有机碳和微生物量碳外，土壤碳、氮各组分均随土层深度加深而呈现递减趋势，土壤碳、氮各组分之间的比值，除MAOM-N/N和MBC/C外，均随土层深度的增加而呈现显著上升趋势；(3)增温对POM-N/MBN和MAOM-N/MBN的影响与土层深度存在明显的交互效应；(4)不同土层氮组分比值对增温的响应与禾草丰度、杂类草丰度、凋落物量、土壤pH值及土壤含水量等因素有关。其中，凋落物...

The responses of soil organic carbon fractions to manipulative climate warming in a saline-alkali grassland of the northern agro-pastoral ecotone

There is great uncertainty in the responses of soil organic carbon (C) to climate warming in the saline-alkali grassland in northern China. In this study, we explored the responses of soil organic C and nitrogen (N) fractions in different soil layers to the manipulative warming using a 5-year continuous warming experiment in a saline-alkali grassland of Youyu, Shanxi Province. The experiment with a randomized block design had been conducted since 2017 at the Youyu Loess Plateau Grassland Ecosystem Research Station of Shanxi Agricultural University, where open-top air chambers (OTCs) were established to simulate climate warming. Our results showed that warming treatments did not significantly affect soil organic C, total N, particulate organic C (POM-C) and N (POM-N), Mineral-associated organic C (MAOM-C) and N (MAOM-N), dissolved organic C (DOC) and N (DON) and microbial biomass C (MBC) and N (MBN) fractions. Moreover, the ratio between soil C and N fractions, with the exception of MAOM-C/MBC which decreased owing to warming treatments, did not significantly change with warming treatments. However, we found that soil depth had a significant effect on soil organic C and N fractions, except for DOC and MBC, where soil C and N fractions showed a decreasing trend with soil depth. In contrast, the ratio between soil C and N fractions, except for MAOM-N/N and MBC/C, increased with soil depth. Warming and soil depth interactively affected POM-N/MBN and MAOM-N/MBN, suggesting a discrepancy between MBN and POM-N or MAOM-N from different soil layers in response to warming. Shifts in the ratio of N fractions of different soil layers under warming treatment may be attributable to shifts in the grass abundance, forb abundance, litter mass, soil pH and soil moisture. Among them, litter mass and soil pH pronouncedly associated with POM-N/MBN and MAOM-N/MBN, grass abundance and forb abundance significantly related to POM-N/N, and soil physicochemical properties such as soil pH and soil moisture correlated with MAOM-N/N. Overall, the results as mentioned above highlight the adaptation of soil organic C and N fractions to short-term climate warming in the saline-alkali grassland. In addition, the ratio of N fractions in different soil layers showed a stronger response to warming treatment compared to soil C fractions. These findings could improve our understanding for the patterns of soil organic C pool in response to climate warming in the saline-alkali grassland, and provide support for the conservation and restoration of fragile grassland ecosystems in northern China.