Data analysis
All data (i.e. δ13C, NSCT and its
components) were first tested for normality with Kolmogorov–Smirnov
tests to assess the within- and between-subject effects in different
tissues of pine (i.e. needle, xylem, phloem) and mistletoe (i.e. leaf,
shoot).
For the wrapping experiment (Exp. 1), a linear mixed model (tree
replicates as random effect) was used for testing the effects of time
(sampling time), irrigation treatment (i.e. non-irrigated vs.
irrigated), wrapping treatment (i.e. wrapping vs. non-wrapped), and
their interactions on the carbon isotopic composition in different
mistletoe tissues (i.e. leaf, shoot).
The assessment of residuals
normality and homoscedasticity were tested before analysis.
For the removal experiment (Exp. 2) (above the girdled branches), the
assessment of residuals normality and homoscedasticity were tested
before analysis. A linear mixed model (tree replicates as random effect)
was used for testing the effects of time (sampling time), irrigation
treatment (i.e. non-irrigated vs. irrigated), removal treatments (i.e.
needle removal for phloem, xylem and mistletoe tissues; mistletoe
removal for pine tissues; and no removal for both pine and mistletoe
tissues), and their interactions on δ13C and
NSCT concentrations. For each sampling time point,
one-way ANOVA and a Tukey-HSD post-hoc test were used to investigate the
difference in δ13C and NSCTconcentrations in different pine and mistletoe tissues under different
irrigation and removal treatments. R version 4.1.0 was used for all
statistical analyses (R Core Team, 2021).