Stem Photosynthesis of Twig and Its Contribution to New Organ Development in Cutting Seedlings of Salix Matsudana Koidz.

The objective of this study was to illustrate the photosynthetic characteristics of current twigs of Salix matsudana Koidz., and clarify the effect of stem photosynthesis on the new organ development in cutting seedlings. Excised twigs were taken as the experimental samples. The response of the stem photosynthesis rate to increasing light intensity and the effective photochemical efficiency of the cross section of the twig were determined. Then, twigs were used as cuttings and exposed to 0, 20, and 100 μmol m⁻² s⁻¹ light intensities, respectively, to achieve distinctive stem photosynthetic rates. After 14 days of treatment, stem water and non-structural carbohydrate (NSC) content, as well as the biomass and carbon isotopic composition, of new organs in the cutting seedlings under different light treatments were examined. The results showed that the gross photosynthetic rate significantly increased within 400 μmol m⁻² s⁻¹ of light intensity, and the maximum rate was approximately 1.27 μmol m⁻² s⁻¹. The effective photochemical efficiency of the PSⅡ of the cortex was significantly higher than the inner tissues in the cross section of the twig. When twig cuttings were exposed to different light intensities, stem water and starch content, as well as bud and root biomass, were significantly higher in the cutting seedling subjected to 100 μmol m⁻² s⁻¹ than the case treated in darkness; however, the bud δ¹³C trend was the opposite. Stem photosynthesis played a positive role in the maintenance of stem water and starch supply for the cutting seedlings, and ¹³C depleted assimilates produced by stem photosynthesis contributed to bud biomass, revealing that stem photosynthesis promotes organ development in cutting seedlings of Salix matsudana.