Coordination among hydraulic, stomatal, and anatomical traits in Prunus dulcis L. cultivars differing in degree of isohydric and anisohydric behavior

Variation in stem xylem anatomy among almond cultivars was associated with differences in hydraulic vulnerability, indicating that anatomical traits contributed more strongly than stomatal behavior to cultivar-level drought responses.

Understanding the mechanisms underlying isohydric and anisohydric behavior in woody species is critical for predicting their performance under increasing drought stress. We combined hydraulic, anatomical, and gas exchange measurements during progressive soil drought and re-watering in three Prunus dulcis cultivars (Avijor, Isabelona, and Soleta) to evaluate how coordinated traits explain drought responses and recovery. Hydroscape analysis confirmed the isohydric–anisohydric ranking previously reported, with Avijor being the most isohydric and Soleta the most anisohydric. Across cultivars, a common sequence of responses was observed: early decline in leaf hydraulic conductivity (K_leaf), followed by turgor loss point (Ψ_TLP), stomatal closure, and onset of embolism. Despite this shared pattern, cultivars differed in key drought thresholds. The more anisohydric cultivars showed more negative Ψ_TLP, and Soleta exhibited greater stem embolism resistance than Avijor. Cultivar differentiation was also clearer in stem xylem anatomy than in leaf traits, with variation in vessel-related traits being consistent with differences in stem vulnerability. By contrast, leaf vulnerability thresholds showed no clear differences among cultivars. Relative K_leaf recovery differed among cultivars, with higher recovery in Soleta than in Avijor, while Isabelona was intermediate. This pattern may reflect that Soleta and Isabelona did not reach water potentials lower than their stem P₅₀ during drought, unlike Avijor. The separation between leaf and stem vulnerability thresholds also varied between cultivars and was greatest in Soleta, suggesting possible inter-cultivar variability in hydraulic vulnerability segmentation. Overall, cultivar-level drought responses in almond were explained by differences in stem embolism resistance, Ψ_TLP, and stem xylem analysis than by stomatal behavior alone.