The integrated effects of projected climate change on cotton growth and physiology.

Abstract

Changes in atmospheric [CO2], temperature, precipitation and consequently atmospheric vapour pressure deficit (VPDa) under projected climate change scenarios present a challenge to crop production. This may have significant impacts on the physiology and yield of cotton and hence the profitability of the Australian cotton industry. Understanding the implications of integrated environmental impacts on cotton is critical for developing cotton systems that are resilient to stresses induced by climate change. Elevated [CO2] generally increases photosynthesis, reduces transpiration and improves leaf- and plant-level water use efficiency (WUE) of well-watered C3 plants , but this effect may be altered by rising temperature and reduced water availability. Cotton responds to changes in vapour pressure deficit (VPD), yet there has been little research on the leaf-level physiological response to altered VPD in field-grown cotton. In addition, a number of studies have investigated the effect of elevated [CO2] and temperature on physiology and growth of a range of cotton cultivars, yet there has not been a comparison between older and current varieties used in Australian production systems to identify if there has been inadvertent selection of beneficial traits for a changing climate. It is important to understand potential interactions as it is likely that multiple variables will be altered with future climatic changes. This thesis aims to investigate the integrated effects of projected climate change (warmer temperature, elevated [CO2], altered VPD and water stress) on physiology, growth and water use of cotton in high-yielding and high-input modern cotton systems in Australia. This will facilitate development of crop management strategies and improve cotton yield and water use efficiencies. This was achieved through a combination of glasshouse and field-based studies. Glasshouse experiments were conducted during 2010 and 2011 at the University of Western Sydney, Richmond, Australia. In these experiments, cotton was grown in sun-lit glasshouse bays in two [CO2] (CA: 400 µL L-1 and CE: 640 µL L-1) and two temperature (TA: 28/17 °C day/night and TE: 32/21 °C day/night) treatments. Field experiments were conducted during the 2011/12 and 2012/13 cotton seasons at the Australian Cotton Research Institute, Narrabri, Australia. The objective of glasshouse experiment I (Chapter 3) was to quantify the physiological and growth capacity of different cotton genotypes to current and future climate regimes. This experiment compared the early-season growth and physiology response of a past (DP 16) and a current (Sicot 71BRF) cotton cultivars grown in ambient and elevated atmospheric [CO2] and two temperature treatments under well-watered conditions. This study demonstrated that elevated [CO2] increased biomass and photosynthetic rates compared with the ambient [CO2] treatment, and that warmer air temperatures (32/21 oC, day/night) also increased plant biomass. Although limited by the comparison of only one older and one modern cultivar, this study indicated that current cultivars may have an advantage over older varieties in future, warmer environments due to smaller, more compact morphology of the modern cultivar. However, no interaction between elevated temperature (TE) and elevated [CO2] (CE) indicated that substantial potential may exist to increase breeding selection of cotton varieties that are responsive to both TE and CE.