Effect of copper stress on photosynthesis of navel orange seedlings

The hydroponic method was used to study the photosynthetic characteristics of navel orange “No.52” seedlings under Cu stress. The study shows that chlorophyll (Chl.) content under 0.1 mmol·L^-1 of Cu increases significantly, but decreases under 5 mmol·L^-1, 20 mmol·L^-1 and 40 mmol·L^-1 of Cu. Carotenoid content decreases with increasing Cu concentration. Net photosynthetic rate and light saturation point reduces under Cu stress as Cu concentration exceeds 5 mmol·L^-1. 0.1 mmol·L^-1 of Cu improves, but 5 mmol·L^-1 and 20 mmol·L^-1 of Cu decrease transpiration rate and stomatal conductance of orange. These parameters do not change significantly under 40 mmol·L^-1 of Cu. At the same time, high Cu concentration (5 mmol·L^-1, 20 mmol·L^-1 and 40 mmol·L^-1) restricts photoreduction activity. The findings indicate that lower Cu concentration improves photosynthesis while high Cu concentration inhabits it.