Atmospheric CO enrichment effect on the Cu-tolerance of the C cordgrass Spartina densiflora.

A glasshouse experiment was designed to investigate the effect of the co-occurrence of 400 and 700ppm CO at 0, 15 and 45mM Cu on the Cu-tolerance of C cordgrass species Spartina densiflora, by measuring growth, gas exchange, efficiency of PSII, pigments profiles, antioxidative enzyme activities and nutritional balance. Our results revealed that the rising atmospheric CO mitigated growth reduction imposed by Cu in plants grown at 45mM Cu, leading to leaf Cu concentration bellow than 270mgKg Cu, caused by an evident dilution effect. On the other hand, non-CO enrichment plants showed leaf Cu concentration values up to 737.5mgKg Cu. Furthermore, improved growth was associated with higher net photosynthetic rate (A). The beneficial effect of rising CO on photosynthetic apparatus seems to be associated with a reduction of stomatal limitation imposed by Cu excess, which allowed these plants to maintain greater WUE values. Also, plants grown at 45mM Cu and 700ppm CO, showed higher ETR values and lower energy dissipation, which could be linked with an induction of Rubisco carboxylation and supported by the recorded amelioration of N imbalance. Furthermore, higher ETR values under CO enrichment could lead to an additional consumption of reducing equivalents. Idea that was reflected in the lower values of ETR/A ratio, malondialdehyde (MDA) and ascorbate peroxidase (APx), guaiacol peroxidase (GPx) and superoxide dismutase (SOD) activities under Cu excess, which could indicate a lower production of ROS species under elevated CO concentration, due to a better use of absorbed energy.