菌根真菌影响森林生态系统碳循环研究进展

森林生态系统在全球碳(C)储量中占据极为重要的地位。菌根真菌广泛存在于森林生态系统中,在森林生态系统C循环过程中发挥重要的作用。阐述了不同菌根类型真菌在森林生态系统C循环过程中的功能,对比了温带/北方森林与热带/亚热带森林中菌根真菌介导的C循环研究方面新近取得的研究结果。发现温带和北方森林的外生菌根(EcM)植物对地上生物量C的贡献相对较小,然而是地下C储量的主要贡献者;以丛枝菌根(AM)共生为主的热带/亚热带森林地表生物量占比较高,表明AM植被对热带/亚热带森林地上生物量C的贡献相对较大。我们还就全球变化背景下,菌根真菌及其介导的森林生态系统C汇功能,以及不同菌根类型树种影响C循环的机制等进行了总结。菌根真菌通过影响凋落物分解、土壤有机质形成及地下根系生物量,进而影响整个森林生态系统的C循环功能。菌根介导的森林C循环过程很大程度上取决于(优势)树木的菌根类型和森林土壤中菌根真菌的群落结构。最后指出了当前研究存在的主要问题以及未来研究展望。本文旨在明确菌根真菌在森林生态系统C循环转化过程中的重要生态功能,有助于准确地评估森林生态系统C汇现状,为应对全球变化等提供重要的依据。

Research progress of mycorrhizal fungal impacts on carbon cycling in forest ecosystems

Forest ecosystems play an extremely vital role in the global carbon (C) storage. Mycorrhizal fungi are ubiquitous in forest ecosystems and have crucial effects on C cycling. Here we reviewed the functions of different types of mycorrhizal fungi driving the C cycle in different forest ecosystems. First, we briefly introduced the important functions of forest ecosystems and mycorrhizal fungi. We also summarized the results of recent studies on C cycling driven by mycorrhizal fungi in temperate and boreal forests, as well as tropical/subtropical forests. It is found that ectomycorrhizal (EcM) plants in temperate and boreal forests contributed less to aboveground biomass C but they were major contributor to belowground C stocks, indicating that the contribution of EcM vegetation to aboveground biomass C is relatively small, while underground C stocks positively correlated with the proportion of EcM plant biomass. However, arbuscular mycorrhizal (AM) fungi dominated in tropical and subtropical forests and had higher aboveground biomass in these ecosystems, indicating that the contribution of AM fungi associated with soil organic C and N pools may even exceed the contribution of soil microbial biomass. Besides, climate change factors such as atmospheric CO₂ enrichment, N deposition, land use change, warming, and drought were potentially important factors affecting the community structure of mycorrhizal fungi and the stability or decomposition of C in both temperate/boreal forests and tropical/subtropical forest biomes. Then, the mechanisms of mycorrhizal fungus-mediated C sink function in forests, and the mechanisms of different mycorrhizal tree species influencing the C cycle were emphasized in this review. In conclusion, the mycorrhizal fungi regulated C cycling function of the whole forest ecosystem by affecting the decomposition of litter, the formation of soil organic matter and the turnover of belowground root biomass. Specifically, EcM fungi had an advantage over free-living fungi in nutrient competition for the decomposition of difficult litter, and the Gargil effect occurred only in forests dominated by difficult organic matter, while AM fungi were unable to directly utilize organic nutrients in the soil, but preferred to utilize "inorganic" nutrients. In addition, mycorrhizal roles in forest C cycle largely depended on the mycorrhizal type of the (dominant) trees and mycorrhizal fungal community structure in forest soils, because mycorrhizal type of the trees had the direct or indirect effects on photosynthetic product allocation across host plants, as well as the number and function of extraradical mycelium and metabolic activity of soil microbes. We also proposed some perspectives in terms of establishing controlled field experimental platform, developing cutting-edge methods or techniques, and strengthening the research on the effects of global changes on mycorrhizal fungi and forest soil C sink function in future. This mini-review highlights the important C cycling function of mycorrhizal fungi which may provide key implications for promoting the soil climate mitigation in forest ecosystems.