Gas exchange of poinsettia leaves from the stock plant through the propagation environment

Gas exchange (photosynthesis and transpiration) and chlorophyll fluorescence measurements were recorded on poinsettia (Euphorbia pulcherrima) leaves on stock plants prior to cutting removal and then on those same leaves after the cuttings were harvested from the stock plant, placed in a simulated postharvest environment for 3 d, and grown on a propagation bench for 28 d. The results demonstrate the changes that occur in photosynthesis and transpiration throughout the propagation cycle due to physiological changes occurring in the plant. Following 3 d of cold storage, the transpiration rate of the cuttings was only 12% of the rate recorded on the stock plants. During the first week in propagation, prior to root initiation, transpiration increased throughout the week. Transpiration rates also returned to levels typical of the stock plant by day 28 in propagation. Photosynthesis rates remained consistently low throughout the first week in propagation, and then began to recover by day 21 in propagation when roots were present. Photosynthesis returned to levels similar to the stock plant by day 28 when the cuttings were fully rooted and ready for transplant. Chlorophyll fluorescence measurements (F_v/F_m) showed no significant change on leaves from the stock plant through the propagation cycle, indicating that photosynthetic apparatus was not damaged during the harvesting, storage and propagation period.