Hydraulic integrity of plant organs during drought stress and recovery in herbaceous and woody plant species.

The article investigates the hydraulic integrity and embolism dynamics of roots, stems, and petioles during drought stress and recovery in one herbaceous species (Helianthus annuus) and five tree species (Populus × canadensis, Acer saccharum, A. saccharinum, Picea glauca, and Tsuga canadensis). It finds that cavitation predominantly occurs in petioles rather than roots or stems in tree species, while all organs in H. annuus exhibit cavitation with increasing severity from root to petiole. Stomatal closure precedes embolism formation or turgor loss across species. Upon rewatering, embolism repair varies by species and organ: petiole vessels recover in Acer species but not in P. × canadensis (which sheds leaves), and roots and petioles recover in H. annuus but stems do not; however, stomatal conductance rarely returns to pre-drought levels. These results support the hydraulic segmentation hypothesis, indicating organ- and species-specific drought responses, with petioles acting as hydraulic safety valves and roots showing high cavitation resistance. The study emphasizes the importance of integrating physiological measures with embolism vulnerability assessments to understand whole-plant drought responses.