Combined effect of elevated CO2 and temperature on the growth and phenology of two annual C3 and C4 weedy species

To evaluate the effects of elevated temperature and CO2 on two annual species of C3 and C4 plants, Chenopodium album (C3) and Setaria viridis (C4), these plants were grown under three different environmental conditions: (1) ambient temperature and CO2 (control), (2) 4 degrees C elevated temperature with ambient CO2 (T4), and (3) combined conditions of 4 degrees C elevated temperature and 1.8 times ambient CO2 (CT4). The plant phonology was generally more affected by increased temperature than elevated CO2 during all growth stages. With a 4 degrees C increase in temperature, the timings of emergence were advanced by approximately 26 days (d) for C. album and approximately 35 d for S. viridis. The flowering times were also advanced, by 50d for C album and by 31.5d for S. viridis. With the advanced phenology observed in the elevated temperature plots, the growth temperatures during the vegetative stage were similar to the values in the control plot. However, the mean temperatures in the elevated temperature plots were significantly higher during the reproductive period than those in the control plot. The biomass and seed weights harvested from C album were significantly decreased, by 47.3% and 14.6%, respectively, under T4 conditions compared to the control, whereas they were dramatically increased, by 33.9% and 114.4%, respectively, in CT4 conditions compared to the control. The biomass of S. viridis grown under CT4 conditions did not differ significantly from that of the control, although it was slightly increased under T4 conditions. Our results suggest that elevated temperature strongly influences biomass production in annual grasses during the reproductive stage compared to the vegetative growth stage and that these effects may be greater in C3 plants than in C4 plants. However, the disadvantages of warming may be considerably attenuated by elevated CO2, especially for C3 grasses. (C) 2011 Elsevier B.V. All rights reserved.