Figure 4. Proportional contribution to xylem water (mean ±SE)
of the water in the fractured bedrock (bedrock; dark blue), deep (20-40
cm; medium blue), and shallow soil layers (0-20 cm; light blue)
resulting from the mixing model, for P. nigra, P. sylvestris, Q.
faginea , and Q. ilex in monospecific (dashed bars) and
four-species mixtures (empty bars) for each sampling date. Asterisks
denote significant differences between diversity levels for a given soil
layers and date (*0.05≥P>0.01; **0.01≥P>0.001;
***P≥0.001).
We observed a significant negative relationship between water source
partitioning (PW), i.e., the average difference between
water-uptake depths, and the soil aridity index (P/PET)
(P<0.001; Fig. 5b). When the soil moisture decreased in the
summer (i.e., decreasing P/PET), PW consistently
increased, indicating stronger water source partitioning. After the
first rain replenished the soil in the fall of 2021, PWdecreased. In contrast, the intense 2022 drought delayed the recovery of
PW in the fall (Fig. 5a).