Why do acquisitive fine-roots exude more carbon: A cost-benefit model simulation

Plants manipulate the activities of microbial decomposition in the rhizosphere, i.e. the so-called rhizosphere effects (REs). The more nutrient-acquisitive plants seem to allocate more carbon (C) to the rhizosphere to meet their nutrient demands. Alternatively, it is probably the fast-growing species are more C leaky. In this study, we induced plant regulation processes on C release and nutrient acquisition to the biogeochemical model of microbial decomposition. We simply increased two parameters, namely root exudation and plant competition capacity  against microbes for available nitrogen. Our model showed that C investment to the rhizosphere and plant nutrient-acquisition capacity with decomposers together determine the cost-benefit balance of rhizosphere effects. For each specific species with a specific nutrient-acquisition capacity, there is an optimal exudation invest for the plant’s best interests. Furthermore, co-existing species can have similar efficiency of C cost against N benefit by optimal pairs of exudation and competition capacity. Our model not only give mathematical explanation why acquisitive plants release more root exudation but also show promising tools to modeling rhizosphere effects at ecosystem levels.