Anatomical and hydraulic responses to desiccation in emergent conifer seedlings

Authors: MILLER, MEGAN - University Of Idaho; RODDY, ADAM - Yale University; BRODERSEN, CRAIG - Yale University; McElrone, Andrew; JOHNSON, DAN - University Of Georgia

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2020
Publication Date: 8/1/2020
Citation: Miller, M., Roddy, A., Brodersen, C.R., McElrone, A.J., Johnson, D. 2020. Anatomical and hydraulic responses to desiccation in emergent conifer seedlings. American Journal of Botany. 107(8):1177-1188. https://doi.org/10.1002/ajb2.1517.
DOI: https://doi.org/10.1002/ajb2.1517

Interpretive Summary:

Technical Abstract: The young seedling life stage is critical for reforestation after disturbance and for species migration under climate change, yet little is known regarding their basic hydraulic function, vulnerability to embolism, or biomechanical responses to drought. Here, we sought to characterize biomechanical responses to drought including hydraulic vulnerability on intact and excised stems, xylem anatomical traits, and impacts on other stem tissues that contribute to vascular and whole plant health under drought. Larix occidentalis, Pseudotsuga menziesii, and Pinus ponderosa (all < 6 weeks-old) were imaged using X-ray computed microtomography during desiccation to assess seedling biomechanical responses with concurrently measured specific hydraulic conductivity (ks) and water potential to assess vulnerability to xylem embolism formation and other tissue damage. In non-stressed samples for all species, pith and cortical cells appeared circular and well-hydrated, but they started to empty and deform with decreasing water potential which resulted in cell tearing and eventual collapse. Despite the severity of this structural damage, the vascular cambium remained well-hydrated even under the most severe drought. There were significant differences between species in vulnerability to xylem embolism formation, with 78% xylem embolism in L. occidentalis by leaf water potential of -2.1 MPa, but only 47.7% and 62.1% in P. ponderosa and P. menziesii at -4.27 and -6.73 MPa, respectively. Similarly, ks dropped close to zero for L. occidentalis by leaf water potential of ~ -2.1 MPa. ks values for P. menziesii and P. ponderosa were highly variable, but these species did maintain higher ks under severe stress compared to L. occidentalis. L. occidentalis seedlings appeared to be more susceptible to drought stress compared to the other two species, but all three maintained hydration of the vascular cambium under severe stress, which could facilitate hydraulic recovery by regrowth of xylem when stress is relieved.