Water stress is the principal environmental factor limiting vegetation gas exchange, growth, survival and primary production globally, with profound effects on ecosystems and human societies. The plant responses to water stress and the underlying mechanisms vary with different time scales considered. Understanding how drought limitation on gas exchange varies among species from contrasting hydro-climates and among time scales is key to predicting the large-scale consequences of drought in the context of climate challenges. We studied the short and long term of drought-responses of gas exchange forEucalyptus species from contrasting hydro-climates in Australia. Species were subjected to long-term experimental treatment with different sustained watering regimes. The study provided evidence for gradual acclimation of carboxylation capacity in the long-term drought. It is concluded the responses of species and plant functional types (PFTs) to different moisture regimes in the long-term may be different, and carbon balance under prolonged drought can be overestimated if acclimation to the prolonged drought is not taken into account. 

This study could provide important implications to climate change adaptation. In particular: (1) time scale is of essence when determining how climate change is affecting the forest die-off due to carbon starvation and/or hydraulic damage; (2) the prediction of drought effects on forest production, biodiversity, and tree range migration, should consider the species-specific and/or PFT-specific eco-physiological acclimation and adaptation during the climate change process; (3) interspecific variation on drought tolerance, acclimation, and adaptation should be highlighted in forest management and/or afforestation in water-limited ecosystems in future climate change scenarios.