Leafy cuttings of Rhododendron catawbiense Michx. ‘Roseum Elegans’ were rooted under 0%, 55%, or 95% shade in a greenhouse. Compared to the low-light treatment, higher light induced high photosynthetic rates, high sucrose and starch levels, and low leaf water potential, but these differences only persisted for the initial part of the 23-week rooting period and did not influence subsequent rooting percentage. However, in cuttings receiving 95% shade, dry weights of leaves and stems and rootball size were relatively small after 23 weeks, suggesting that growth was reduced by lack of photosynthate. The reduced size of cuttings rooted under 95% shade apparently did not affect vigor because the size of the above-ground portion of all plants was equal after 2 months of growth in a greenhouse.
Root formation on leafy cuttings of Pisum sativum L. ‘Alaska’ was reduced by about 50% when net photosynthesis was adjusted to the compensation point by reducing the light intensity, reducing the CO2 concentration, or by blocking CO2 exchange with an antitranspirant. Rooting was also reduced by 50% when cuttings were given only enough photoperiod at saturating light to maintain a carbon balance similar to that of the treatments which reduced net photosynthesis to the compensation point. In addition to decreasing rooting, these treatments lowered sucrose and glucose levels in the basal portion of the cuttings compared to controls. Our photosynthesis and carbohydrate data indicate that the supply of current photosynthate to the base of pea cuttings is important to rooting.