Elevated CO2 in air changes photosynthetic response of Hordeum vulgare and Bromus secalinus to cadmium pollution in soil

The integrated effects of increased atmospheric CO2 and heavy metals pollution may have important implications for plant growth. Elevated atmospheric CO2 can affect plant defences through its significant effects on plant growth. Some studies have found that elevated CO2 can decrease oxidative stress and lead to increased rates of growth and development. Among the numerous heavy metals contaminants, cadmium (Cd) is one of the most toxic and prevalent pollutants of surface soils. Cd is a toxic heavy metal that can be readily taken up by plants, and contamination of soils with Cd is a widespread problem that affects plant growth, defence, development, and metabolite production. The aim of this study was to investigate the response of photosynthetic system and growth of summer barley (Hordeum vulgare L.) and rye brome (Bromus secalinus L.) to different cadmium concentrations effect under elevated CO2 in atmosphere. To study the combined effect of cadmium (300 mgCd/kg and 500 mgCd/kg substrate) and elevated atmospheric concentration of CO2 (400, 700 and 1400 ppm CO2) on photosynthetic parameters and growth of barley and brome, the pot experiments were conducted in closed controlled environment plant growth chambers. The growth and response of photosynthetic system were evaluated. The results showed that barley was more sensitive to Cd impact under all investigated CO2 concentrations. The strongest negative effect of Cd on photosynthetic performance was detected under current (400 ppm) CO2 concentration for both plants. Increasing CO2 concentration increased photosynthetic rate and decreased the negative effect of Cd. The effect of Cd on stomatal conductance under elevated CO2 also varied: for barley it increased, while for brome it decreased and the result of that was decreased water use efficiency for barley and increased – for brome. Photosynthetic pigments of barley also were more sensitive to Cd effect, but the losses were lower under elevated CO2. Statistically significant effect of Cd on biomass was detected only for barley and elevated CO2 it reduced but only at 700 ppm. This study highlights that the photosynthetic response of investigated plants under cadmium stress at elevated CO2 concentrations changes and the response is species dependent.