Wrapping effects on 13C assimilates in
mistletoe tissues (Exp. 1: wrapping)
Irrigation had no significant effects on the 13C
assimilates of mistletoe tissues in the wrapping experiment, whereas the
wrapping treatment had a strong effect on the 13C
accumulation in mistletoe tissues (Table 1).
Strong
labeling signals were found in the non-wrapped mistletoe leaves and
shoots, while in the wrapped mistletoe clusters no 13C
signal was found in leaves or shoots (Fig. 3). The peak value of
Δδ13C in non-wrapped leaves occurred approximately 8 h
after the labeling started, after which point Δδ13C
values decreased gradually (Fig. 3a). Δδ13C values
reached a peak in wrapped mistletoe shoots at the first sampling time
after labeling, remained at a relatively stable high level until 15 d
after labeling, and decreased slowly thereafter (Fig. 3b).
Removal
effects on carbon assimilates in pine and mistletoe tissues (Exp. 2:
girdling and removal)
The irrigation treatment and its interaction with other factors (time or
removal treatment) did not affect Δδ13C or NSC
concentration (NSCT, sugars, starch) in the pine tissues
(Table 2). However, there was a direct effect of the removal treatments
on the carbon assimilates in host tissues (Table 2). Mistletoe removal
resulted in significantly lower needle Δδ13C at 24 h
after labeling (Fig. 4a), but did not affect needle NSC concentrations
(Table 2, Fig. 5a). Mistletoe removal did not affect new carbon
assimilates in the host phloem (Figs. 4b, 5b) but led to significantly
lower Δδ13C in the pine xylem tissue at 3 and 15 d
after labeling (Figs. 4c, 5c). When the needles were removed, no
significant 13C signals were found anymore in host
phloem or xylem (Fig. 4b, c). Needle and mistletoe removal did not
affect the NSC concentrations in pine phloem (Fig. 5b). Needle removal
decreased the host xylem NSC concentrations, while such effects were not
observed in the mistletoe removal treatment (Fig. 5c).
Irrigation significantly (P< 0.05) or marginally
significantly (P<0.10) influenced the Δδ13C
and NSC concentrations (except sugars) in both mistletoe leaves and
shoots (Table 2), and host needle removal also significantly affected
the carbon assimilates and NSC concentrations in both mistletoe leaves
and shoots (Table 2). In addition, host needle removal interacted with
irrigation to significantly affect Δδ13C and NSC
concentrations in mistletoe leaves and Δδ13C in
mistletoe shoots (Table 2). Mistletoes on trees grown under dry control
conditions tended to have higher Δδ13C levels in
leaves and shoots than those on irrigated trees, irrespective of host
needle removal, but the higher Δδ13C levels of
mistletoes were found when needles were removed in trees grown under dry
conditions (Fig. 4d, e). Similarly, NSC concentrations in mistletoe
leaves were higher in the control compared with the irrigated trees, but
mainly when the pine needles were removed (Fig. 5d, e).
Table 1: Results of
linear mixed models for Δδ13C values (uptake and
incorporation of 13C) of bulk material in different
tissues of Viscum album ssp. austriacum in the wrapping
experiment (Exp. 1). Degrees of freedom (df) and F-values are given for
time, irrigation treatment and wrapping treatment (i.e. wrapped vs
non-wrapped; n = 3).