Growth and development of cotton (Gossypium hirsutum L.) in response to CO₂ enrichment under two different temperature regimes

An increase in atmospheric CO₂ concentration ([CO₂]) together with other climate change factors could greatly affect agricultural productivity. Understanding the impact of the change in atmospheric [CO₂] in conjunction with the ongoing global change is crucial to prepare for mitigation and any adaptation for future agricultural production. The main goal of this project was to study the time-course pattern of cotton plant growth in response to [CO₂] and temperature to investigate the hypothesis that whether response to elevated [CO₂] would change at different temperatures. An experiment was conducted in the controlled-environment chambers of the Georgia Envirotron with two different day/night temperatures levels, e.g., 25/15°C and 35/25°C, and three CO₂ concentrations, e.g., 400, 600 and 800μmoll⁻¹. The experimental design was completely randomized with four replicates (plastic containers) per treatment. Growth analysis was conducted at bi-weekly intervals during the growing season. In addition, leaf area, leaf dry mass, root dry mass, square dry mass, boll dry mass and total above dry mass per plant were also measured at each sampling. Plant traits, including plant height, number of leaves, number of squares and number of bolls were recorded weekly. The number of days to emergence, squaring, flowering and maturity were also observed. The results showed that by increasing [CO₂] to 600μmoll⁻¹ total biomass increased at both temperature levels, but a further increase of [CO₂] up to 800μmoll⁻¹ increased total biomass only at the temperature of 35/25°C. Throughout the growing season, there was no significant effect of [CO₂] levels on LAI. Increasing temperature from 25/15°C to 35/25°C had a positive impact on LAI across all CO₂ levels (P <0.05). Increasing CO₂ from 400 to 600μmoll⁻¹ significantly increased the number of squares by 31.4%, but a further increase to 800μmoll⁻¹ caused a 6.6% decrease (non-significant) in the number of squares. The interactive effects of [CO₂] and temperature indicated that at a higher temperature, CO₂ would be more beneficial as we proceed towards the end of the growing season. However, further studies are needed to really understand the interaction between higher [CO₂] and temperature levels and cultivar characteristics.