微生物介导的碳氮循环过程对全球气候变化的响应

土壤是地球表层最为重要的碳库也是温室气体的源或汇。自工业革命以来,对土壤温室气体的容量、收支平衡和通量等已有较多研究和估算,但对关键过程及其源/汇的研究却十分有限。微生物是土壤碳氮转化的主要驱动者, 在生态系统碳氮循环过程中扮演重要的角色,对全球气候变化有着响应的响应、适应及反馈,然而其个体数量,群落结构和多样性如何与气候扰动相互关联、进而怎样影响生态系统过程的问题仍有待进一步探索。从微生物介导的碳氮循环过程入手,重点讨论微生物对气候变化包括温室气体(CO₂,CH₄,N₂O)增加、全球变暖、大气氮沉降等的响应和反馈,并由此提出削减温室气体排放的可能途径和今后发展的方向。

Responses of microbes-mediated carbon and nitrogen cycles to global climate change

As a significant global carbon and nitrogen sink, soils are also acting as the source or net sink of greenhouse gases. Many investigations and assessments on carbon pools, fluxes and net carbon balance have been carried out on soil, while little knowledge is available about the related key processes and mechanisms. Soil microbes are the main drivers in carbon and nitrogen cycles, which lead to a positive or negative feedback for global climate change. Though it has already known that microbes play an important role in the process of soil ecosystems, it is still unclear whether the relationship between global change and microbial dynamics (such as diversity and abundance) and the mechanisms in regulating the soil biogeochemical processes that they underpin. In this review, we discussed the direct and indirect impact of global climate change, such as greenhouse gas emissions (CO₂, CH₄ and N₂O), warming and nitrogen deposition, on microbial-mediated carbon and nitrogen cycles. The effects of increased CO₂ levels on microbial communities are often indirect through altering the release of labile sugars, organic acids and amino acids from plants, which can affect microbial growth and activity. The main direct influence of global climate change on microbial activity and function are likely to be caused by changes in temperature and moisture content, which will cause variation of physiology or community structure of the microbes. We also demonstrated the microbial feedback and interaction with global climate change. It is generally accepted that changes in the composition and diversity of soil microbial communities will have little effect on CO₂ emission at the terrestrial level, because the CO₂ production results from numerous microbial processes. Unlike CO₂ emission, the CH₄ emission is more directly influenced by methanogenesis process, which is carried out by a group of anaerobic archaea. The production of N₂O from natural and anthropogenic source is dominated by microbial nitrification and denitrification, although the relative contribution of these processes to net N₂O flux is still less known. The disturbance caused by land manipulation (like land use type) and land management practices (such as fertilization) may stimulate the rate of organic matter decomposition and microbial respiration, because it provides greater access to both substrate and oxygen.As the complex of soil properties and different microbial community physiology, the multifactor, molecular and biochemical tools were combined and suggested in studying microbial response to climate change. At the ecosystem level, stable isotope probing technique has shown its powerful role in linking the microbial diversity and abundance to the estimation and attribution of gas emission. The possibility in mitigating greenhouse gas emissions through managing terrestrial microbial processes is also addressed in order to provide potential suggestions for future microbial studies in the scope of global climate change. There have been some achievement in mitigation of greenhouse gas, such as the application of nitrification inhibitor (dicyandiamide, DCD) to nitrogen-rich pasture soil, which can significantly reduce the direct emission of N₂O from urine patches through inhibiting the activity of ammonia oxidizing microorganisms. Further studies are urgently needed on microbial mechanisms in adaptation to climate change and mitigation of greenhouse gas emissions.