Elevated [CO2] mitigates the impacts of heat stress in eucalyptus seedlings

Given ongoing climate changes and their impact on plant growth and development, CO2 effects have been extensively studied, and evidence indicates that elevated CO2 concentration ([CO2]) may mitigate the impacts of warming. However, the interaction between these two environmental factors and how they impact the physiology of eucalyptus seedlings under tropical conditions remain largely unknown. Here, we evaluated the alterations in morphological, physiological and metabolic traits of seedlings of two eucalyptus clones exposed either to elevated [CO2] or warming or both (using a mini-Free- Air CO2 Enrichment (FACE) and a temperature (T-FACE system). Most parameters (e.g. growth, and gas exchange parameters) were negatively affected in response to warming. By contrast, elevated [CO2] improved plant biomass accumulation via changes in primary metabolism. Such changes mainly involved depletion of starch concentration in both clones, whereas changes in the amino acids (AA) profile revealed global (increases in branched-chain AA) or clone specific (increases in aromatic AA) changes. Elevated [CO2] mitigated the negative effects of environmental warming in plants exposed to these two factors simultaneously. Taken together, our results indicate that in a future scenario featuring increased [CO2] and temperature the process of metabolic and physiological acclimation will likely lead to the maintenance of seedling growth