Exudates of Carboxylates by Roots and Their Implications for Nutrient, Contaminant and Carbon Dynamics in Soil

Rhizosheath carboxylates originate from plant root exudates, soil microbial activity, and soil organic matter decomposition. This review provides a comprehensive bibliometric analysis of critical discussions on the role of rhizosheath carboxylates in soil ecosystems by examining factors influencing their release, and their implications for nutrient availability, contaminant behavior, and carbon dynamics. Root exudates comprise numerous compounds, including enzymes, polysaccharides, primary metabolites such as carbohydrates, amino acids, and carboxylates, and secondary metabolites like phenols, glucosinolates, vitamins, and plant hormones. In response to biotic and abiotic stresses, soil microorganisms also release carboxylates as part of their adaptive strategies. Their release, concentration, and persistence in the rhizosheath fluctuate over time, which is influenced by various factors, including soil type, plant species, nutrient availability, microbial activity, and environmental conditions. These carboxylates play a key role in mobilizing carbon, nutrients, and contaminants, thus influencing their bioavailability to plants and microbes. While the dynamic and transient nature of these root exudates allows plants to respond to changing environmental conditions and nutrient demands by adjusting their exudation patterns, it poses significant challenges to the measurement and quantification of root exudates. This challenge can be overcome by developing techniques for the in situ measurement of root carboxylate exudation.