Drought stress increases total C released from roots

Abstract

Background and Aims. Root exudation and rhizodeposition are critical pathways for plant carbon (C) allocation to soil, influencing soil organic C stability and ecosystem functioning under changing climates. However, the effects of drought stress on these below-ground processes remain poorly understood. We provide an updated and comprehensive assessment of the current state of knowledge on how drought stress affects root-derived C fluxes (root exudates, rhizodeposition) across diverse functional types and experimental setups to direct future research. Methods. We conducted a meta-analysis to quantify how drought stress affects total C and other compound classes in root exudation and rhizodeposition. Key Results. Our analysis included 40 data points spanning diverse functional types, ecosystems, sampling methods and experimental conditions. We observed that root-released total C significantly increased in response to drought stress. Among compound classes, carbohydrates and organic acids also increased in response to drought stress, suggesting these compound classes may underlie total C responses in root exudation and rhizodeposition. The variables that explained the most variance in total C response ratio were ecosystem, flowering type, cotyledon type, functional type and drought intensity. Conclusions. To direct future research, our analysis identified knowledge gaps, particularly the need for studies to examine trees and shrubs, field-based research, broader drought intensity ranges, and measurements of total C, compound classes and specific compounds when possible. Improving our understanding of root-derived C responses to stress is crucial for predicting terrestrial C cycling dynamics and ecosystem function under increased drought frequency and intensity.