Rising atmospheric CO2, warmer air temperatures, higher Vapour Pressure Deficit (VPD) and reduced water availability as a consequence of climate change is likely to affect cotton production. Previous field and glasshouse studies in Australian cotton systems have shown that warmer air temperatures may increase stomatal conductance and transpiration, resulting in reduced leaf-level water use efficiency. Increased photosynthesis and increased vegetative biomass under scenarios of projected climatic conditions will not necessarily equate to higher yields. Furthermore, elevated CO2 may potentially exacerbate the negative effects of warmer temperature in cotton, leading to large reductions in water and resource use efficiencies. Therefore, further studies were required to explore management strategies for cotton grown in high temperature, high CO2 environments, thereby enabling sustainable and efficient cotton production systems in the future.

To enhance the current understanding of cotton system adaptation to climate variability and plan for projected climate change, a combination of controlled environment glasshouse and field-based studies were conducted to assess the integrated effects of warmer temperatures and elevated atmospheric CO2 concentration on cotton growth, physiology and water use. Overarching aims were to (1) investigate the interactive effects of atmospheric vapour pressure deficit (VPD) and soil water deficit on the physiology of cotton; (2) identify potential management practices that mitigate the interactive effects of climate change; (3) improve understanding of leaf to canopy level scaling; and (4) better model and predict the impact of future climate scenarios on water use and yield of cotton.

Glasshouse studies showed that increasing VPD stimulated stomatal closure across a range of temperatures. Soil water deficit reduced stomatal conductance of cotton at all temperatures measured, particularly at lower VPD compared with well-watered plants given the same VPD. Therefore, drier climatic conditions may reduce stomatal conductance, although transpiration increases with warmer temperatures, within the range of at 50% water deficit that was tested in our study.

Glasshouse studies showed that fruit loss may greatly increase the vegetative growth rate (VGR) of cotton; however, mepiquat chloride applications were also shown to reduce the VGR of cotton that had lost fruit in warmer temperature and elevated atmospheric CO2 environments. Similarly, our field studies demonstrated that vegetative biomass was controlled by the application of mepiquat chloride in two out of the three seasons, although observations of increased difficulty in defoliating cotton plants grown at warmer temperatures and elevated CO2 suggest that understanding timing of defoliants in future climate scenarios may require further research. Therefore, this research suggests that mepiquat chloride may be a successful method of controlling excessive vegetative growth in future climates of warmer temperatures and elevated atmospheric CO2.

The climate chambers were used to measure the leaf and canopy level responses of cotton grown in warmer temperature and elevated CO2 environments; however, further research may use modelling to further link these responses. We also used a multi-faceted approach to better model and predict the impact of future climate scenarios of water use and yield of cotton. Our research indicated that climatic changes, such as an increase in the number of seasonal day degrees, have already occurred across several key locations throughout the Australian cotton industry. These findings may help define adaptation strategies by linking regions with similar past and present climatic conditions. On-going research requires a multi-faceted approach that incorporates model simulations, glasshouse and field studies to better our understanding and knowledge of system responses to projected environmental conditions for Australian cotton regions. The outcomes of the broad research into the effects of climate change on Australian cotton systems, has been summarised in our review to industry, “An overview of recent research into the effects of climate change and extreme weather events on Australian cotton systems”, published by CottonInfo.