Effects of photosynthetic photon flux and carbon dioxide concentration on the photosynthesis and growth of grafted pepper transplants during healing and acclimatization

In the production of grafted transplants, healing and acclimatization are the most critical processes for survival. We investigated the influence of the photosynthetic photon flux (PPF) and the carbon dioxide (CO 2 ) concentration during healing and acclimatization on the photosynthetic characteristics and growth of grafted pepper transplants to determine the optimum environmental conditions for healing and acclimatization in a healing chamber with artificial lighting source. Grafted pepper transplants were healed and acclimatized under two levels of CO 2 (374 or 1,013 μmol·mol −1 ) and four levels of PPF (dark, 50, 98 or 147 μmol·m −2 ·s −1 ) for six days. The CO 2 exchange rates of the grafted pepper transplants significantly increased with increasing PPF during healing and acclimatization. The CO 2 exchange rates were higher under elevated CO 2 concentrations than ambient CO 2 concentration. The effect of CO 2 enrichment was greater in low light intensity. The CO 2 exchange rates at 50, 98 or 147 μmol·m −2 ·s −1 under elevated CO 2 concentrations were 511, 261, and 172%, respectively, compared to the ambient CO 2 concentrations. The increase of photosynthesis led to an improvement in growth. The SPAD value, dry weight and leaf area were greater under higher PPF and CO 2 concentrations. PPF also influenced the anatomical structures of the leaves, and the palisade and spongy tissue cells of the leaves irradiated with higher PPF were aligned more densely, with more chloroplasts and small empty space. When compared to the tunnel in the greenhouse with natural light, healing and acclimatization under high CO 2 (1,000 μmol·mol −1 ) and PPF (150 μmol·m −2 ·s −1 ) conditions in the healing chamber promoted the growth and graft union formation of grafted pepper transplants. The results suggested that high-quality grafted pepper seedlings could be achieved by healing and acclimatization in a healing chamber where optimal conditions such as high PPF and CO 2 were maintained within the range evaluated in this experiment.