Abstract:

Invasive alien species greatly change the forest composition and coverage, and reduce the species richness and diversity therein, which have profoundly altered the terrestrial carbon cycling processes and subsequently influenced the accuracy of carbon calculation that is theoretically based on the terrestrial forest coverage. In recent decades, many scientists have put efforts on the carbon cycle changes in invaded ecosystems and showed that the invasion stages, environmental factors and species compositions in communities influence the processes of carbon cycling. However, whether plant invasions serve as a carbon sink or source function is still obscure, and the main uncertainty comes from the underground ecosystem. In the present paper, we reviewed the recent studies on the effects of exotic plant invasions upon ecosystem carbon cycling. With an emphasis on the underground carbon cycling processes, we analyzed the influences of environment parameters, plant physiological characters, and the relationships between plants and surrounding soil biota. Generally, climate parameters may affect the speed and direction of forest coverage substitution, but are insufficient for explaining the inconsistences resulted from different invasion species at a local scale or even from the same species in the same study. Invasive plants are able to assimilate and install more carbon into ecosystems because of the photosynthesis priority, while the carbon output, usually in the form of root exudates and debris, would depend on the substance composition and degradation rate, as well as soil properties. Soil biota, as an important component of underground carbon, modulates both carbon input and output in ecosystems, and the net flux determines the carbon sink or source function, offering an important rational explanation for the uncertainty. In the end, we raised several research prospects regarding to the key processes of terrestrial carbon cycling, by considering the disciplinary development in the context of global change and the requirement to control invasive alien species.

Key words: exotic plant invasions, forest coverage, ecosystem carbon cycling, underground carbon cycling, priority characters in photosynthesis, soil biota

摘要：

外来植物入侵改变陆地生态系统的植被覆盖与组成，降低生态系统内物种丰富度和多样性，影响系统内碳循环过程，进而影响基于植被组成估算生态系统碳储量结果的准确性。近年来，不少学者展开了植物入侵对生态系统碳循环的影响研究，发现入侵阶段、被入侵生态系统的环境因素及群落组成等均影响生态系统内碳循环过程及碳储量；然而，对于被入侵生态系统的“碳源汇”功能认定目前仍存在较大争议，其中最不确定的为生态系统地下部分。文章综述了国内外关于植物入侵影响生态系统碳循环研究的最新进展，并就被入侵生态系统地上和地下碳循环过程的改变系统阐述了入侵引起的碳源、汇变化；同时，以地下生态过程为核心，从气候因素、植物个体特征及其与周围生物的牧食关系等方面阐述了植物入侵影响地下碳过程的机理。总体上，气候因素可在大区域范围内影响植被更替的速度与物种多样性的发展方向，但不能解释入侵在气候环境一致的特定区域内所引起的差异性影响；入侵植物因叶片光合优势往往会向生态系统输入更多有机碳，当其以凋落物和根系分泌物等形式向系统外输出时则受物质组成、分解速率及土壤环境等多因素的影响；土壤生物既是土壤有机碳的重要组分，也是有机碳向土壤输入与输出的调节者，通过改变有机碳的净通量来调节碳源、汇功能，这可能是造成入侵植物碳源、汇争议的重要原因之一。最后，文章就植物入侵影响生态系统碳循环的关键环节，结合全球变化背景下的学科发展和入侵防控需求，提出若干未来亟需深入研究的科学问题。

关键词: 外来植物入侵, 植被覆盖, 生态系统碳循环, 土壤碳循环, 植物光合优势特征, 土壤生物