Effects of elevated CO2 concentration and temperature on the mixed-culture grown wild mustard (Sinapis arvensis L.) response to auxin herbicide.

Recently, there has been growing concern over the potential impact of CO concentration and temperature on herbicide efficacy. The aim of the study was to examine the influence of single elevated CO (400 vs. 800 ppm) and elevated CO in combination with temperature (21 °C vs. 25 °C) on the effects of auxin herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) (0.5-2 × field recommended rate) to wild mustard (Sinapis arvensis L.) grown in mixed-culture with spring barley (Hordeum vulgare L.). MCPA had a detrimental effect on aboveground and belowground biomass, content of chlorophylls, enzymatic and non-enzymatic antioxidants and induced oxidative stress. The significant decline in photosynthetic rate, stomatal conductance and transpiration with MCPA dose was detected. Elevated CO reinforced MCPA efficacy on S. arvensis: sharper decline in biomass, photosynthetic rate and antioxidant enzymes and more pronounced lipid peroxidation were detected. Under elevated CO and temperature, MCPA efficacy to control S. arvensis dropped due to herbicide dilution because of increased root:shoot ratio, higher activity of antioxidants and less pronounced oxidative damage. Reinforced MCPA impact on weeds under elevated CO resulted in higher H. vulgare biomass, while decreased MCPA efficacy under elevated CO and temperature reduced H. vulgare biomass.