Drought-induced fiber water release and xylem embolism susceptibility of intact balsam poplar saplings

Authors: CHU, CHEYENNE - University Of British Columbia; MOMAYYEZI, MINA - University Of California, Davis; STOBBS, JARVIS - Canadian Light Source Inc; SOOLANAYAKANAHALLY, RAJU - Agriculture And Agri-Food Canada; McElrone, Andrew; KNIPFER, THORSTEN - University Of British Columbia

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2023
Publication Date: 10/19/2023
Citation: Chu, C., Momayyezi, M., Stobbs, J.A., Soolanayakanahally, R.Y., McElrone, A.J., Knipfer, T. 2023. Drought-induced fiber water release and xylem embolism susceptibility of intact balsam poplar saplings. Physiologia Plantarum. 175:e14040. https://doi.org/10.1111/ppl.14040.
DOI: https://doi.org/10.1111/ppl.14040

Interpretive Summary: Balsam poplar (Populus balsamifera) is an economically and ecologically important and widespread tree species across North America. Little is known about differential susceptibility to drought-induced embolism amongst genotypes of this species, which raises questions regarding survival during early establishment in native habitats and their use in poplar breeding programs. Using X-ray microcomputed tomography (microCT), we determined in-vivo stem xylem embolism susceptibility and tissue-specific filling patterns (fiber, pith and bark) and investigated underlying vessel anatomical traits. For genotypes Gillam-5 (‘Gil-5’, native to Manitoba boreal forest, 56º N latitude) and Carnduff-9 (‘Car-9’, native to Alberta Prairies, 49º N latitude), our data show that Gil-5 is significantly less susceptible to drought-induced embolism than Car-9 with a stem water potential threshold for 50% embolism at -2.1MPa compared to -1.7MPa, respectively. The relatively low embolism susceptibility in Gil-5 was linked to higher frequencies of smaller vessel diameters compared to Car-9. Intervessel pits detected on the shared vessel wall were less abundant in Gil-5 than Car-9, which may limit embolism spread in Gil-5. Vessel elements were aligned in Gil-5 whereas a slight offset in vessel elements was observed for some vessels in Car-9 that may have contributed to embolism formation. While the genotypes started with similarly water filled matrices, fiber emptying as drought progressed was most pronounced in Gil-5 with the onset of mild-moderate stress indicating a role of fiber water release in minimizing the risk of embolism formation. In conclusion, a combination of vessel anatomical traits and water release dynamics determines drought-induced embolism susceptibility in intact Balsam poplar saplings.

Technical Abstract: Balsam poplar (Populus balsamifera) is an economically and ecologically important and widespread tree species across North America. Little is known about differential susceptibility to drought-induced embolism amongst genotypes of this species, which raises questions regarding survival during early establishment in native habitats and their use in poplar breeding programs. Using X-ray microcomputed tomography (microCT), we determined in-vivo stem xylem embolism susceptibility and tissue-specific filling patterns (fiber, pith and bark) and investigated underlying vessel anatomical traits. For genotypes Gillam-5 (‘Gil-5’, native to Manitoba boreal forest, 56º N latitude) and Carnduff-9 (‘Car-9’, native to Alberta Prairies, 49º N latitude), our data show that Gil-5 is significantly less susceptible to drought-induced embolism than Car-9 with a stem water potential threshold for 50% embolism at -2.1MPa compared to -1.7MPa, respectively. The relatively low embolism susceptibility in Gil-5 was linked to higher frequencies of smaller vessel diameters compared to Car-9. Intervessel pits detected on the shared vessel wall were less abundant in Gil-5 than Car-9, which may limit embolism spread in Gil-5. Vessel elements were aligned in Gil-5 whereas a slight offset in vessel elements was observed for some vessels in Car-9 that may have contributed to embolism formation. While the genotypes started with similarly water filled matrices, fiber emptying as drought progressed was most pronounced in Gil-5 with the onset of mild-moderate stress indicating a role of fiber water release in minimizing the risk of embolism formation. In conclusion, a combination of vessel anatomical traits and water release dynamics determines drought-induced embolism susceptibility in intact Balsam poplar saplings.