图2. 根系分泌物诱导的土壤碳(C)矿化或根际激发效应机理。A, 传统的微生物共代谢机理——根系分泌物输入后主要促进微生物生长和活性, 并伴随着土壤C矿化加快。B, 新提出的根际激发效应机理——大量土壤C由于矿物保护而不能被微生物直接利用, 根系分泌物输入后通过络合作用和溶解反应等非微生物过程打破或者降低有机-矿质复合体稳定性, 将保护态C释放出来而增加了保护态C的微生物可达性。

Fig. 2. Proposed mechanisms for the exudate-induced acceleration of the microbial mineralization of soil organic carbon in the rhizosphere (i.e., rhizosphere priming effects). A, The traditional view is that root exudate compounds stimulate microbial growth and activity via co-metabolism, and so increase the overall physiological potential of the decomposer community for carbon mineralization. B, The alternative mechanism proposed here takes into account that large quantities of soil C are inaccessible to microbes owing to associations with mineral phases. Root exudates that can act as ligands effectively liberate C through complexation and dissolution reactions with protective mineral phases, thereby promoting its accessibility to microbes and accelerating its loss from the system through microbial mineralization.