Location: Crops Pathology and Genetics ResearchTitle: Variations in xylem embolism susceptibility under drought between intact saplings of three walnut species
|Knipfer, Thorsten - University Of California|
|Barrios-masias, Felipe - University Of Nevada|
|Cuneo, Italo - University Of California|
|Bouda, Martin - Yale University|
|Albuquerque, Caetano - University Of California|
|Brodersen, Craig - Yale University|
Submitted to: Tree Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2018
Publication Date: 5/30/2018
Citation: Knipfer, T., Barrios-Masias, F., Cuneo, I., Bouda, M., Albuquerque, C., Brodersen, C., Kluepfel, D.A., McElrone, A.J. 2018. Variations in xylem embolism susceptibility under drought between intact saplings of three walnut species. Tree Physiology. 38(8):1180-1192. https://doi.org/10.1093/treephys/tpy049.
Interpretive Summary: Walnuts are grown commercially worldwide, and Juglans species native to varied habitats hold the potential of providing new rootstock material with improved resistance to drought. Using X-ray microCT, we investigated in vivo the effect of drought-induced water stress on stem xylem embolism susceptibility (and repair following re-watering) in relation to vessel anatomical traits in Juglans species. Among the species tested, saplings of J. microcarpa (arid habitat) were most resistant to drought-induced embolism. In comparison, J. ailantifolia (mesic habitat) appeared to be the most vigorous species under well-watered conditions (largest canopy and highest stomatal conductance) but was relatively susceptible to drought-induced embolism linked to the presence of vessels with increased pit size and frequency. Embolism repair following re-watering for 40 days was negligible in intact saplings of all three Juglans species. For Juglans, our preliminary study indicates that pit characteristics (among various other vessel anatomical traits) are a promising target to more efficiently screen Juglans germplasm collections for drought resistance and embolism susceptibility.
Technical Abstract: Plant germplasm collections containing genotypes from varied habitats hold remarkable potential to improve drought resistance for commercially cultivated crops. Walnuts (Juglans spp.) have broad native ranges, but key physiological parameters associated with whole-plant water movement remain largely unknown. In this study, synchrotron-based x-ray microCT was used to evaluate in-vivo embolism susceptibility/repair, vessel size distributions, xylem network connectivity, and pit characteristics in stem xylem of 2-year old saplings of three Juglans species; analyses were complemented with investigation of leaf transpiration. J. ailantifolia (native to mesic habitats) exhibited higher drought-induced embolism susceptibility as compared to J. microcarpa and J. hindsii (both native to arid habitats). Higher frequencies of large diameter vessels were detected in J. ailantifolia and J. microcarpa, whereas smaller diameter vessels of reduced embolism susceptibility were found in J. hindsii. For interconnected vessels of larger diameter, pit size and density was generally high in J. ailantifolia and J. hindsii but not in J. microcarpa. Xylem connectivity analysis predicted that only around 10% of vessels were interconnected suggesting a minor role of drought-induced embolism spread by air-seeding in all three Juglans species. Leaf transpiration was highest in J. ailantifolia, intermediate in J. microcarpa, and lowest in J. hindsii, while drought-induced reductions in transpiration were most severe in J. ailantifolia. Following re-watering, embolism repair was negligible in all three species and transpiration only recovered substantially for J. microcarpa (least embolism susceptible). In conclusion, data suggest two different strategies for xylem embolism resistance in Juglans species native to aridlands that are both consistent with the ‘rare pit hypothesis’: relative to the more susceptible J. ailantifolia, J. microcarpa has vessels of larger diameter with limited pitting while J. hindsii has vessels of relatively small diameter in which pit size and density is minimized. These traits could provide targets for breeding efforts aimed at selecting walnut germplasm with superior drought resistance.