The Effect of Atmospheric Carbon Dioxide Concentration on the Growth and Chlorophyll Fluorescence Characteristics of Hazelnut Leaves under Cadmium Stress

Abstract

To understand the response of hazelnut to the increased concentration of carbon dioxide (CO2) under cadmium (Cd) pollution stress, this paper used an artificial open top chamber to control the CO2 concentration (at 370 and 750 μmol·mol−1) and to study the effects of an elevated CO2 concentration on the growth and photosynthetic capacity of hazelnut leaves under different levels of Cd stress. The results showed that the increase in atmospheric CO2 concentration has a tendency to alleviate the inhibition of plant growth caused by Cd. The net photosynthetic rate rose significantly, although the transpiration rate and stomatal conductance of hazelnut leaves decreased slightly with the rise in CO2 concentration. The rise in CO2 concentration had no significant effect on the activity of the photosystem Ⅱ (PSII) reaction center in hazelnut leaves. Under Cd stress conditions, the rise in CO2 concentration significantly enhanced the PSII hazelnut leaves’ photochemical activity, which promotes the PSII receptor’s electron transfer capacity side and alleviates the degree of damage to the oxygen-evolving complex and the thylakoid membrane of the PSII donor side. The number of active reaction centers per unit area of hazelnut leaves, and the proportion of energy absorbed by PSII that is used for photosynthetic electron transfer, increased under severe stress conditions, which in turn reduced the energy proportion that was used for heat dissipation, providing CO2’s effective fixation energy in the dark reaction. In conclusion, the rise in the CO2 concentration enhances hazelnut’s heavy metal resistance by improving the PSII function under Cd stress conditions.