Rising temperature may negate the stimulatory effect of rising CO2 on’growth and physiology of Wollemi pine (Wollemia nobilis)

Rising atmospheric [CO2] is associated with increased air temperature, and this warming may drive many rare plant species to extinction. However, to date, studies on the interactive effects of rising [CO2] andwarming have focussed on just a few widely distributed plant species. Wollemi pine (Wollemia nobilisW.G.Jones, K.D.Hill, & J.M.Allen), formerly widespread in Australia, was reduced to a remnant population of fewer than 100 genetically indistinguishable individuals. Here, we examined the interactive effects of three [CO2] (290, 400 and 650 ppm) and two temperature (ambient, ambient + 4 C) treatments on clonally-propagated Wollemi pine grown for 17 months in glasshouses under wellwatered and fertilised conditions. In general, the effects of rising [CO2] and temperature on growth and physiology were not interactive. Rising [CO2] increased shoot growth, light-saturated net photosynthetic rates (Asat) and net carbon gain. Higher net carbongainwasdue to increasedmaximumapparent quantumyield and reducednon-photorespiratory respiration in the light, which also reduced the light compensation point. In contrast, increasing temperature reduced stem growth and Asat. Compensatory changes inmesophyll conductance and stomatal regulation suggest a narrow functional range of optimal water and CO2 flux co-regulation. These results suggest Asat and growth of the surviving genotype of Wollemi pine may continue to increase with rising [CO2], but increasing temperatures may offset these effects, and challenges to physiological and morphological controls over water and carbon trade-offs may push the remnant wild population of Wollemi pine towards extinction. Additional keywords: elevated [CO2], growth, photosynthesis, photosynthetic capacity, photosynthetic light response, pre-industrial [CO2], stomatal conductance. Received 18 September 2014, accepted 4 May 2015, published online 24 June 2015