Exposure to preindustrial, current and future atmospheric CO2 and temperature differentially affects growth and photosynthesis in Eucalyptus

To investigate if Eucalyptus species have responded to industrial-age climate change, and how they may respond to a future climate, we measured growth and physiology of fast( E. saligna) and slow-growing (E. sideroxylon) seedlings exposed to preindustrial (290), current (400) or projected (650 mu L L-1) CO2 concentration ([CO2]) and to current or projected (current +4 degrees C) temperature. To evaluate maximum potential treatment responses, plants were grown with nonlimiting soil moisture. We found that: (1) E. sideroxylon responded more strongly to elevated [CO2] than to elevated temperature, while E. saligna responded similarly to elevated [CO2] and elevated temperature; (2) the transition from preindustrial to current [CO2] did not enhance eucalypt plant growth under ambient temperature, despite enhancing photosynthesis; (3) the transition from current to future [CO2] stimulated both photosynthesis and growth of eucalypts, independent of temperature; and (4) warming enhanced eucalypt growth, independent of future [CO2], despite not affecting photosynthesis. These results suggest large potential carbon sequestration by eucalypts in a future world, and highlight the need to evaluate how future water availability may affect such responses.