根际激发效应的发生机制及其生态重要性

孙悦, 徐兴良

Mechanisms of rhizosphere priming effects and their ecological significance

SUN Yue, XU Xing-Liang, Yakov KUZYAKOV

图2 根际激发效应的发生机制: 当土壤氮受限时, 植物将较多的光合产物投资到地下, 根际微生物利用根际沉积物获取碳和能量, 增加微生物数量和活性, 促进微生物胞外酶的分泌, 分解有机质释放可利用氮, 产生正的根际激发效应(图左); 当土壤氮富集时, 减少了微生物对养分的需求, 根际微生物偏好利用根系分泌物, 减少胞外酶的分泌, 而植物也减少向地下的碳分配, 导致根际微生物数量减少和活性降低, 抑制了有机质分解, 产生负的根际激发效应(图右)。绿箭头、蓝箭头和红箭头分别代表由植物、土壤微生物和胞外酶主导的生态过程; 箭头的粗细表征通量的大小或过程的强弱。可利用性氮库中的黄色代表来自土壤有机质矿化作用产生的可利用性氮, 其色块面积大小代表来自有机质矿化作用的数量。

Fig. 2 Mechanism of rhizosphere priming effects. At low nutrient levels (left), plants allocate more photosynthates to belowground and supply soil microorganisms with carbon and energy. As a result, microbial biomass and activities increase and enhance production of extracellular enzymes by the rhizosphere microorganisms to decompose soil organic matter and release nutrients. Therefore, a positive priming effect takes place. In contrast, at high nutrient levels (right), microorganisms have less demand for nutrients and thus preferentially utilize root exudates, leading to reduced production of extracellular enzymes. Moreover, as plants invest less photosynthates in belowground, microbial biomass and activities will decrease. As a result, the decomposition of soil organic matter slows down and a negative priming effect occurs. The green, blue, and red arrow-lines represent the ecological processes mediated by plants, soil microorganisms, and exoenzymes, respectively. The thickness of an arrow-line indicates its relative magnitude of a flux or intensity of a process. Yellow colour of the available nitrogen pool indicates mineral nitrogen derived from mineralzation of soil organic matter. The area of the yellow colour represents the amount of mineral nitrogen derived from mineralzation of soil organic matter.