Controls of atmospheric carbon transfer to soil by root exudates

The interaction between plants and soil plays a decisive role in controlling the formation of soil organic matter (SOM) - a critical factor for the functioning of ecosystems and the mitigation of climate change. Carbon compounds that plants release into the soil as root exudates have important impacts on the stability of SOM and can shift with climate change. Yet, a generalizable understanding of the biotic and abiotic controls on the relationships between plant-soil carbon exchanges and large-scale carbon fluxes and SOM formation is still lacking.

Here, I compile data from different forest ecosystems to illustrate: 1) the response of root exudates in distinct ecozones to species mixing, 2) the impact of drought and recovery on plant-soil interactions, and 3) the quantitative correlation between rhizodeposition and ecosystem carbon uptake, as well as its association with SOM formation.

Observations point to a connection between carbon exudation and root growth, with greater root growth leading to reduced exudation rates and vice versa. However, exudation rates across diverse ecozones were highly responsive to even minor alterations in the sampling method, suggesting careful considerations when comparing datasets from different studies. The rhizosphere showed increased levels of stabilized SOM that endured after drought, suggesting the potential for rhizodeposition to enhance the preservation of soil carbon.

Current data indicates that a substantial fraction of carbon in the atmosphere is allocated towards root exudates, likely serving as a crucial element in the ability of ecosystems to respond to climate change. Understanding plant-soil interactions in a global context requires aligning sampling methods within an ecozonal context.