林木根源有机C对大气CO2浓度升高的响应

林木根源有机C包括根系通过根枯落物、根系(根共生菌丝)分泌物和根共生菌周转3条途径向土壤输入的有机C.它是森林生态系统中一个重要的、潜在的C汇.综述了根源有机C与其微生物对CO2浓度升高的响应.虽然对根系寿命的变化尚不清楚,但CO2浓度升高将导致根系生物量、生产量、死亡量和分泌物的增加;同时,CO2升高亦促使根共生菌生物量的增加而增加了共生菌的C归还潜力,表明CO2升高使根源有机C的输入增加了.CO2浓度升高情况下,根系化学性质(根N浓度降低)和形态特征(根直径增加)的这些变化均有利于增加土壤C的吸存;而根分布深度的降低则对土壤C吸存不利;CO2浓度升高对根分泌物和根共生菌质量的影响研究则极少.CO2浓度升高下土壤微生物活性和群落组成的变化存在较大的不确定性.目前CO2浓度升高下林木根源有机C对森林长期C吸存的贡献仍很不清楚.

Responses of Root-derived Organic Carbon to Elevated CO2 in Forest Ecosystems

Root-derived organic carbon is composed of three compartments: root detritus, root exudates and root symbionts, which represents a large important and potential C sink in forest ecosystems. The known responses of root derived organic carbon and heterotrophic microbes to elevated CO_2 were reviewed. Overall, increases in root biomass, productivity, and exudation indicate an augmentation of C inputs into the soil via roots, although changes in root lifespan are still unclear and may modify this flux positively or negatively. Altogether, changes in root chemistry and morphology that may augment soil C storage under elevated CO_2 include decreased N concentration and wider root diameter. Alternately, a shift in rooting depth upwards in the soil profile may increase average turnover rates of root detritus. Effects of CO_2 concentration on C qualities of root exudates and root symbionts are the least understood components discussed here. Changes of soil heterotropic microbial activity and community under elevated CO_2 still remained large uncertainties. By far, the contributions of root derived organic carbon to long-term soil carbon sequestration under the context of elevated CO_2 are not clear yet.