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ABSTRACT Plant roots are the critical interface between plants, soil, and microorganisms, and respond dynamically to changes in water availability. Although anatomical adaptations of roots to water stress (e.g., the formation of root cortical aerenchyma) are well documented, it remains unclear whether these responses manifest along the length of individual roots under both water deficiency and water overabundance. We investigated the anatomical responses ofTripsacum dactyloidesL. to both drought and waterlogging stress at high spatial resolution. Nodal roots were segmented into one‐centimeter sections from the tip to the base, allowing us to pinpoint regions of maximal anatomical change. Both stressors overall increased the proportion of root cortical aerenchyma, but metaxylem responses differed: waterlogging increased the proportion of the stele that was occupied by metaxylem with fewer but larger vessels. Drought significantly increased root hair formation within two centimeters of the root tip. The most pronounced anatomical changes occurred 3–7 cm from the root tip, where cortical cell density declined as aerenchyma expanded. These findings highlight spatial variation in root anatomical responses to water stress and provide a framework that can inform sampling protocols for various other data types where sampling effort is limiting (e.g., microbiome, transcriptome, proteome). 

Premise: Plant roots are the critical interface between plants, soil, and microorganisms, and respond dynamically to changes in water availability. Although anatomical adaptations of roots to water stress (e.g., the formation of root cortical aerenchyma) are well documented, it remains unclear whether these responses manifest along the length of individual roots under both water deficiency and water over-abundance. Methods: We investigated the anatomical responses of Tripsacum dactyloides L. to both drought and flood stress at high spatial resolution. Nodal roots were segmented into one-centimeter sections from the tip to the base, allowing us to pinpoint regions of maximal anatomical change. Results: Both stressors increased the proportion of root cortical aerenchyma, but metaxylem responses differed: flooding increased vessel area whereas drought led to smaller vessels, with both showing a lower number of vessels. Drought also significantly increased root hair formation, but only within the first two centimeters. The most pronounced anatomical changes occurred 3-7 cm from the root tip, where cortical cell density declined as aerenchyma expanded. Discussion: These findings highlight spatial variation in root anatomical responses to water stress and provide a framework integrating various other data types where sampling effort is limiting (e.g., microbiome, transcriptome, proteome).