Abstract
During secondary growth, forest trees can modify the anatomy of the wood produced by the vascular cambium in response to environmental conditions. Notably, the trees of the model angiosperm genus, Populus, reduce the risk of cavitation and hydraulic failure under water stress by producing water-conducting vessel elements with narrow lumens, which are more numerous and more interconnected with each other. Here, we determined the genetic architecture of vessel traits affecting hydraulic physiology and resilience to water stress. Vessel traits were measured for clonally replicated genotypes of a unique Populus deltoides x nigra population carrying genomically defined insertions and deletions that create gene dosage variation. We found significant phenotypic variation for all traits measured (mean vessel diameter, height-corrected mean vessel diameter, vessel frequency, height-corrected vessel frequency, vessel grouping index, and mean vessel circularity), and that all traits were under genetic control and showed moderate heritability values, ranging from 0.32 to 0.53. Whole-genome scans of correlations between gene dosage and phenotypic traits identified quantitative trait loci for tree height, mean vessel diameter, height-corrected mean vessel diameter, height-corrected vessel frequency, and vessel grouping index. Our results demonstrate that vessel traits affecting hydraulic physiology are under genetic control, and both pleiotropic and trait-specific quantitative trait loci are found for these traits.
Highlights
Wood is the water conducting tissue of tree stems, and the anatomical features of wood can have profound effects on water transport and vulnerability to hydraulic failure during water stress (Rodriguez-Zaccaro and Groover, 2019)
mean vessel diameter (MVD) and Vessel frequency (VF) are known to predictably scale with tree height (TH); larger trees tend to have wider and less numerous vessels compared to smaller trees at the same sampling height (Olson et al, 2014)
Both MVD and VF are known to be highly correlated to tree height, where larger trees have wider and less numerous vessels compared to smaller trees at the same sampling height (Olson et al, 2014)
Summary
Wood (secondary xylem) is the water conducting tissue of tree stems, and the anatomical features of wood can have profound effects on water transport and vulnerability to hydraulic failure during water stress (Rodriguez-Zaccaro and Groover, 2019). Secondary growth can be altered to produce wood anatomy and vessel morphologies that mitigate water stress during drought or maximize water conduction for fast growth under permissive conditions (Tyree, 1989; Tyree and Sperry, 1989; Tyree and Zimmermann, 2002). To what degree these changes reflect the passive or indirect responses of development to environmental conditions, as opposed to genetically regulated responses, remains unclear
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