喀斯特系统生物地球化学循环及对全球变化的响应

生物地球化学循环是地球系统物质循环的核心，是维系地表生态系统稳定和人类社会可持续发展的重要基础。然而，气候变化以及人类的过度干扰可能会显著改变表层地球系统中的生物地球化学循环过程，尤其是脆弱的喀斯特生态系统。特殊的多孔隙关键带结构也加速了喀斯特地区物质循环及其对外界环境变化的响应，影响了不同尺度的物质循环和生物地球化学过程。本研究主要综述了宏观尺度（气候变化）、中尺度（人类活动）和微观尺度（微生物活动）的环境变化对喀斯特地区生物地球化学循环的影响。结果表明多要素变化导致喀斯特地区物质循环受到强烈影响，气候变化、人类活动和微生物活动及其耦合关系对喀斯特地区生物地球化学循环的调控作用具有重要意义。最后，本研究强调了现有研究的局限性并指出未来研究的挑战与方向，即未来应从系统研究（如地球关键带）的视角出发，将多尺度观测－分析与综合模型集成研究并举，从而构建多源多尺度耦合的过程和系统模型，进而为阐明喀斯特系统的演变规律和动力学机制、实现喀斯特地区的生态保护和高质量发展提供理论基础。 

Biogeochemical cycles of karst systems and their response to global change

Biogeochemical cycles are the core of matter cycling in the earth system, and are critical to sustaining ecosystem stability and the development of human society. However, climate change and excessive human interference may significantly alter biogeochemical cycles in surface earth systems, especially fragile karst ecosystem. Meanwhile, the special porous critical zone structure in karst regions accelerates the material circulation and its response to the change of external environment, which affects the circulation of matter and biogeochemical process at different scales. Thus, this review mainly emphasized the effects of environmental changes on biogeochemical cycles in karst regions at macroscale (climate change), mesoscale (human activities), and microscales (microbial activities). The main contents are as follow.(1) Climate change (including climate warming and precipitation anomaly) is a direct representation of global change, which not only influence the stability of ecosystem in the karst regions, but also determine local biogeochemical process and material circulation. Although climate warming may enhance the carbon sink function of the aquatic ecosystem in karst region, the watershed carbon sink effect would change with the increase of the warming degree. Moreover, disasters and extreme climate have a strong impact on the ecologically fragile karst regions, but sometimes also have important negative feedback significance to the restoration and reconstruction of regional ecosystem. Furthermore, climate warming can directly or indirectly promote soil respiration intensity by improving biological factors (e.g., physiological activity of underground roots) and abiotic factors (e.g., enzyme activity), but whether it can offset the weakening of soil respiration caused by the decrease of soil moisture content should be further studied. In addition to climate warming, precipitation anomaly also significantly affects soil respiration and watershed nutrient fluxes in karst critical zone, which have important impacts on global carbon cycle and local aquatic ecosystem security. Significantly, due to the coupling relationship between temperature and precipitation, single-factor analysis may not be able to comprehensively assess the impact of climate change on biogeochemical cycles. Therefore, laboratory and field experiments should be combined to comprehensively evaluate the impact of climate change on biogeochemical cycles and feedback on ecosystem stability in karst regions in future work.(2) The impact of human activities on the environment and biogeochemical cycles in karst regions is multi-dimensional, especially land use change, urbanization and water conservancy projects. Land use conversion and vegetation cover change not only change the structure and function of the ecosystem in karst regions, but also change the nutrient cycling process of the ecosystem, thereby affecting the local biogeochemical cycling process. Moreover, urbanization in karst regions will significantly increase the carbon storage in urban systems. Therefore, a coupling system of urban-suburb-rural ecosystem should be established to formulate appropriate environmental management policies through reasonable allocation and sharing of resources in the future. Furthermore, the construction of water conservancy projects in karst watershed not only change the transportation and transformation processes of river particles and nutrients, but also change the geochemical behavior of Dissolved Inorganic Carbon (DIC) in river water, thus affecting the watershed carbon cycle. As we know, human activities have greatly changed the biogeochemical cycles in karst regions and led to new ecological and environmental problems. Therefore, reasonable measures should be taken under the premise of scientific evaluation in order to achieve ecological protection and sustainable development in karst regions.(3) Microbes drive biogeochemical cycles through metabolic activities and respond rapidly to changing environmental conditions to maintain global ecosystem stability. Compared to non-karst regions, the unique karst structure changes the diversity and abundance of microbes. As we know, biodiversity is changing at an unprecedented rate as a result of global change. Climate change affects biogeochemical cycles through controlling microbial community structure and biomass in karst regions. In addition, nutrients addition caused by human activities also affected the functional diversity and community structure of soil microbes in karst regions. And long-term fertilization not only significantly changed the availability of carbon and nitrogen in soil profile in karst regions, leading to differentiation of soil microbial community, but also changed the coupling relationship among different elements (e.g., C, N, P, S). Microbes play a vital role in biogeochemical cycles, which should be further studied in the future under the circumstances of climate change and intensified human activities.As above, multi-factor changes have strongly influenced the matter cycling in karst regions, climate change, human activities, microbial activities and their coupling relationship are vital to regulate biogeochemical cycles. Meanwhile, we also stressed the limitations of existing research and pointed out the challenges and direction of future research. In the future, we should combine multi-scale monitoring-analysis and integrated model research from the perspective of system research (e.g., earth critical zone), so as to establish a multi-source and multi-scale coupling process and system model. Through the above methods, the evolution rules and dynamic mechanism of karst system are clarified, and the theoretical basis for ecological protection and high-quality development in karst regions are provided.