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.