Response of stomatal sensitivity to an elevated carbon dioxide atmosphere

Earth is undergoing anthropogenic induced climate change yet it is unclear what the reaction of plants will be to an increase in carbon in the atmosphere, an element that is vital to their growth. As the interface between the atmosphere and plant stomata's long term acclimation to elevated carbon dioxide levels is important for predictions to changes in water, nutrient and carbon cycles of the future. While a reduction in stomata) conductance is well documented there is a lack of knowledge regarding the alteration in stomatal sensitivity to environmental conditions. The Ball et al (1987) model of stomata) sensitivity relates stomata) conductance (g5 ) to the photosynthetic assimilation rate (A), relative humidity (h) and [CO2] at the leaf's surface in a linear model, where m is the slope and go the baseline stomata) conductance (y-axis intercept) given as: g5=go+m (A.h/[CO2]). This model is often upscaled and used in modelling to relate transpiration rates, soilwater cycles and potential climate change scenarios. In a glasshouse experiment at the University of Melbourne Creswick campus Nipponbare rice, Eucalyptus tricarpa, Eucalyptus grandis, Acacia aneura and Acacia melanoxylon were subjected to ambient [CO2] (400 ?mol mol-1) and elevated [CO2] (700 ?mol mol-1) treatments. The plants stomata) sensitivity was measured using an Infra-Red Gas Analyser (LiCor6400) altering the chamber conditions of light, relative humidity and [CO2]. Linear regression was then conducted on the data to calculate Ball et al (1987) models. It was found that the two Acacia species reduced their sensitivity under elevated [CO2]; with m reducing by 97% for A. aneura and 91% for A. Melanoxylon, while E. tricarpa significantly increased its slope, by 315%. These species Ball et al (1987) models may have to be reparametised under elevated [CO2] conditions, particularly when predicting future water and carbon cycles. E. grandis and the Nipponbare rice did not significantly alter their stomatal sensitivity. Nipponbare rice was the only species to significantly alter its baseline stomatal conductance