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 <i>in situ</i> measurement of root carboxylate exudation.

根际鞘（rhizosheath）羧酸盐主要来源于植物根系分泌物（root exudates）、土壤微生物活性及土壤有机质分解。本综述针对根际鞘羧酸盐在土壤生态系统中的作用展开全面文献计量分析，系统考察了影响其释放的各类因素，以及其对养分有效性、污染物行为与碳动态的调控作用。根系分泌物包含多种化合物，涵盖酶类、多糖、碳水化合物、氨基酸与羧酸盐等初级代谢产物，以及酚类、硫代葡萄糖苷、维生素与植物激素等次级代谢产物。为应对生物与非生物胁迫，土壤微生物也会将释放羧酸盐作为自身适应性策略的组成部分。这类羧酸盐在根际鞘中的释放量、浓度与持久性随时间动态波动，其变化受到土壤类型、植物物种、养分有效性、微生物活性及环境条件等多种因素的调控。这类羧酸盐在活化碳、养分与污染物方面发挥关键作用，进而影响其在植物与微生物中的生物有效性。尽管这类根系分泌物的动态性与瞬时性使得植物可通过调整分泌模式，响应不断变化的环境条件与养分需求，但这也为根系分泌物的检测与定量带来了显著挑战。可通过开发用于根系羧酸盐分泌的原位（in situ）检测技术来攻克这一难题。