State Key Laboratory of Grassland Agro-ecosystems, Key Laboratory of Grassland Livestock Industry Innovation, Ministry of Agriculture and Rural Affairs, Engineering Research Center of Grassland Industry, Ministry of Education, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou 730020, PR China.
Flathead Lake Biological Station, University of Montana, Polson, MT 59860, USA; Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA; Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai 519087, PR China.
Sci Total Environ. 2020 Jun 20;722:137910. doi: 10.1016/j.scitotenv.2020.137910. Epub 2020 Mar 12.
Grasslands across the world are being degraded due to the impacts of overgrazing and climate change. However, the influences of grassland degradation on carbon (C), nitrogen (N), and phosphorus (P) dynamics and stoichiometry in soil ecosystems are not well studied, especially at high elevations where ongoing climate change is most pronounced. Ecological stoichiometry facilitates understanding the biogeochemical cycles of multiple elements by studying their balance in ecological systems. This study sought to assess the responses of these soil elements to grassland degradation in the Qinghai Lake watershed on the Qinghai-Tibet Plateau (QTP), which has an average elevation of >4000 m and is experiencing serious grassland degradation due to its sensitivity and vulnerability to external disturbances. Substituting space for time, we quantified normalized difference vegetation index to gauge grassland degradation. C, N, and P concentrations and their molar ratios in soil and in soil microbial biomass were also measured. The results showed that grassland degradation decreased the concentrations of C and N, as well as the ratios of C:P and N:P in soil. The soil became relatively more P rich and thus N limitation is anticipated to be more apparent with grassland degradation. Moreover, C, N, and P concentrations in soil microbial biomass decreased with increased grassland degradation. C:N:P ratios of soil microbial biomass were highly constrained, suggesting that soil microorganisms exhibited a strong homeostatic behavior, while the variations of microbial biomass C:N:P ratios suggest changes in microbial activities and community structure. Overall, our study revealed that grassland degradation differentially affects soil C, N, and P, leading to decreased C:N and N:P in soil, as well as decreased C, N, and P concentrations in soil microbial biomass. This study provides insights from a stoichiometric perspective into microbial and biogeochemical responses of grassland ecosystems as they undergo degradation on the QTP.
由于过度放牧和气候变化的影响，世界各地的草原正在退化。然而，草原退化对土壤生态系统中碳（C）、氮（N）和磷（P）动态和化学计量的影响还没有得到很好的研究，特别是在海拔较高的地区，那里的气候变化最为明显。生态化学计量学通过研究生态系统中多个元素的平衡来促进对生物地球化学循环的理解。本研究旨在评估青藏高原青海湖流域这些土壤元素对草原退化的响应，该地区平均海拔超过 4000 米，由于对外界干扰的敏感性和脆弱性，正遭受严重的草原退化。本研究采用替代时间的方法，通过量化归一化植被指数来衡量草原退化。还测量了土壤和土壤微生物生物量中 C、N 和 P 的浓度及其摩尔比。结果表明，草原退化降低了 C 和 N 的浓度，以及土壤中 C:P 和 N:P 的比值。土壤变得相对更富磷，因此随着草原退化，预计 N 限制将更加明显。此外，土壤微生物生物量中 C、N 和 P 的浓度随着草原退化的加剧而降低。土壤微生物生物量的 C:N:P 比值受到高度限制，这表明土壤微生物表现出强烈的内稳态行为，而微生物生物量 C:N:P 比值的变化表明微生物活性和群落结构的变化。总的来说，我们的研究表明，草原退化对土壤 C、N 和 P 产生了不同的影响，导致土壤中 C:N 和 N:P 降低，以及土壤微生物生物量中 C、N 和 P 的浓度降低。本研究从化学计量学的角度提供了青藏高原草原生态系统在退化过程中微生物和生物地球化学响应的见解。
