Defoliation tests
We conducted exploratory tests involving artificial defoliation of the
invasive and native species from April to September in 2018 and 2019.
Stems of the invasive and native species were cut into approximately 15
cm long segments that each had one node, and any leaves attached to the
nodes were removed. Afterward, the cuttings were cultivated in plastic
pots (15 cm) filled with jiffy substrate (Jiffy Products International
B.V., Moerdijk, The Netherlands). Each species was grown in more than 30
pots, which were placed under shade conditions during the first week
after planting. The regenerated plantlets were then grown under
greenhouse conditions and watered daily. When the potted plants reached
approximately 20 cm in height, 1.1-m bamboo sticks were inserted into
the soil of the pots as climbing media for the plants. After reaching
40-50 cm in height, the potted plants of each species were evenly
divided into two groups. One group was allowed to continue to grow under
normal conditions, serving as the control. The other group was subjected
to complete artificial defoliation for 30 days, in which all newly grown
leaves were removed at 2-3 d intervals. Every 10 days, the lengths of
the stems of both invasive and native species were measured. On day 20
of defoliation, gas exchange and structural observations were performed
on the stems of the invasive and native species, and chlorophyll
fluorescence was determined. After 30 days of defoliation, the survival
rate of treated plants was determined. The average survival rates were
calculated based on three replications.
To examine how stem photosynthesis changed in the invasive species,
another batch of potted plants of the invasive species was prepared and
treated as mentioned above. The changes in photosynthetic pigments
(chlorophyll) and nonphotosynthetic pigments (anthocyanins), stomatal
behavior, gas exchange and chlorophyll fluorescence,
photosynthesis-related proteins (D1 and Rubisco) and chloroplast
ultrastructure of the stems of the defoliation group were compared with
those of the stems and leaves of the normal-growth group.