Data from: Anatomical and hydraulic responses to desiccation in emergent conifer seedlings

Premise of the study: 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 or
vulnerability to drought. Here, we sought to characterize responses to
desiccation including hydraulic vulnerability, xylem anatomical traits,
and impacts on other stem tissues that contribute to hydraulic
functioning. Methods: 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 hydraulic conductivity
( k s ) and water potential (Y) to assess vulnerability to xylem embolism
formation and other tissue damage. Key Results: 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 Y
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 Ψ 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. Conclusions: 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.