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
regulate ΨL more conservatively than plants with
resistant xylem. We evaluated if this paradigm applied to three
important eastern US temperate tree species, Quercus alba L.,
Acer saccharum Marsh., and Liriodendron tulipifera L., by
synthesizing 1600 ΨL observations, 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 occurs 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.