Water source partitioning
To estimate the plot-level vertical water source distribution in the
mixed forest plots, we calculated the belowground water source
partitioning at the community level (PW, unitless) from
the sum of the differences in either the natural abundance of
δ2H or δ 18O in plant water between
all interacting species in every four-species mixtures for each sampling
date. As different water uptake depths between trees correspond to
greater differences in the xylem water stable isotope within a tree
cluster, higher PW indicates that the trees are taking
up water from more distant water sources from each other. Therefore, to
calculate PW based on δ2H, we used the
following equation developed by Grossiord et al. (2018):
PW = |δ2HPN -
δ2HPS| +
|δ2HPN -
δ2HQF| +
|δ2HPN -
δ2HQI| +
|δ2HPS -
δ2HQF| +
|δ2HPS -
δ2HQI| +
|δ2HQF -
δ2HQI| (Equ. 1)
where δ2HPN,
δ2HPS,
δ2HQF, and
δ2HQI correspond to
δ2H of P. nigra, P. sylvestris, Q. faginea, andQ. ilex , respectively. As the PW resulted from
δ18O and δ2H weighted similarly,
only the PW based on δ2H was further
used in this paper (Fig. S4).