2. Abstract
The coordination of plant leaf water potential (ΨL)
regulation and xylem vulnerability to embolism is fundamental for
understanding the tradeoffs between carbon uptake and risk of hydraulic
damage. There is a general consensus that trees with vulnerable xylem
more conservatively regulate ΨL than plants with
resistant xylem. We evaluated if this paradigm applied to three
important eastern US temperate tree species, Quercus albaL., Acer saccharum Marsh., and Liriodendrontulipifera L., by synthesizing 1600 ΨLobservations, 122 xylem embolism curves, and xylem anatomical
measurements across ten forests spanning pronounced hydroclimatological
gradients and ages. We found that, unexpectedly, the species with the
most vulnerable xylem (Q. alba ) regulated ΨL less
strictly than the other species. This relationship was found across all
sites, such that coordination among traits was largely unaffected by
climate and stand age. Quercus species are perceived to be among
the most drought tolerant temperate US forest species; however, our
results suggest their relatively loose ΨL regulation in
response to hydrologic stress occurrs with a substantial hydraulic cost
that may expose them to novel risks in a more drought-prone future. We
end by discussing mechanisms that allow these species to tolerate and/or
recover from hydraulic damage.