European Journal of Sustainable Agroecosystems

Background: Rhizosphere carbon (C) allocation is a fundamental process governing terrestrial ecosystem functioning by regulating plant–microbial interactions, soil organic matter dynamics, and nutrient cycling. Environmental stresses such as drought, salinity, nutrient deficiency, and heavy metal toxicity alter the distribution of belowground carbon, influencing rhizosphere processes and ecosystem resilience. However, the mechanisms underlying stress-induced carbon allocation and their ecological consequences remain incompletely understood.

Objective: This review aims to systematically synthesize research published between 2015 and 2025 on the mechanisms of stress-induced rhizodeposition and its effects on microbial recruitment, functional diversity, and soil priming. It also compares major exudate collection methodologies and identifies methodological limitations and knowledge gaps in current research.

Method: A systematic review of 32 high-impact studies indexed in Scopus, Web of Science, and PubMed was conducted. The selected studies were evaluated to compare experimental approaches, including hydroponic exudate sampling and in situ isotopic labeling, and to assess evidence on stress-induced rhizosphere carbon allocation, microbial responses, and methodological biases.

Results: The reviewed evidence indicates that environmental stress shifts rhizosphere carbon allocation from passive carbon leakage to active, signal-mediated exudation involving compounds such as organic acids, phenolics, and strigolactones. These exudates enhance the recruitment of stress-tolerant plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF), thereby improving plant adaptation to adverse conditions. Nevertheless, contradictory findings remain regarding the effects of drought on total belowground carbon flux, largely due to differences in experimental duration, sampling methods, and spatial resolution. The review also identifies major research gaps, including limited long-term field studies, insufficient investigation of non-linear multi-stress interactions, and inadequate spatial resolution of existing rhizosphere sampling techniques.

Conclusion: Stress-induced rhizosphere carbon allocation is an active and adaptive mechanism that plays a central role in shaping plant–microbe interactions and ecosystem functioning under environmental stress. Future research should integrate multi-omics approaches, including metagenomics, metatranscriptomics, and exometabolomics, with advanced imaging technologies such as imaging mass spectrometry and microfluidic soil-on-a-chip platforms to resolve the spatiotemporal dynamics of the rhizosphere. These advances will support the development of climate-resilient agricultural systems and provide valuable guidance for researchers, agronomists, and environmental policymakers.