Effects of elevated carbon dioxide and elevated temperature on morphological, physiological and anatomical responses of Eucalyptus tereticornis along a soil phosphorus gradient

Eucalypts are likely to play a critical role in the response of Australian forests to rising atmospheric CO2 concentration ([CO2]) and temperature. Although eucalypts are frequently phosphorus (P) limited in native soils, few studies have examined the main and interactive effects of P availability, [CO2] and temperature on eucalypt morphology, physiology and anatomy. To address this issue, we grew seedlings of Eucalyptus tereticornis Smith across its P-responsive range (6-500 mg kg(-1)) for 120 days under two [CO2] (ambient: 400 mu mol mol(-1) (C-a) and elevated: 640 mu mol mol(-1) (C-e)) and two temperature (ambient: 24/16 degrees C (T-a) and elevated: 28/20 degrees C (T-e) day/night) treatments in a sunlit glasshouse. Seedlings were well-watered and supplied with otherwise non-limiting macro- and micro-nutrients. Increasing soil P supply increased growth responses to C-e and T-e. At the highest P supplies, C-e increased total dry mass, leaf number and total leaf area by similar to 50%, and T-e increased leaf number by similar to 40%. By contrast, C-e and T-e had limited effects on seedling growth at the lowest P supply. Soil P supply did not consistently modify photosynthetic responses to C-e or T-e. Overall, effects of C-e and T-e on growth, physiological and anatomical responses of E. tereticornis seedlings were generally neutral or negative at low soil P supply, suggesting that native tree responses to future climates may be relatively small in native low-P soils in Australian forests.