Relationship between leaf hydraulic traits and xylem water stable
isotope
With increasingly dry conditions in the summer, the xylem
δ18O and δ2H decreased for oaks and
increased for pines in the four-species mixtures, leading to contrasting
relationships between xylem δ18O and the leaf
hydraulic traits (Figs. 6 & S4; Table S2). With decreasing xylem
δ18O, Ψpd, ΔΨ, and
gs significantly increased for pines, suggesting that
deeper water uptake resulted in lower water stress and higher gas
exchange. For oaks, decreasing xylem δ18O led to lower
Ψpd, ΔΨ, and gs(P<0.001; Fig. 6), indicating lower gas exchange despite
deeper water sources. These relationships were only significant in the
four-species mixtures and not in the monospecific plots (Fig. 6).