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Tree growth enhancement under elevated [CO₂] is much smaller than originally anticipated; yet carbon overabundance can lead to increased wood carbon storage and to stomatal downregulation and hence reduced water-use. Notably, all three outcomes increase tree drought resistance. Here we studied growth, water relations, and nonstructural carbohydrates of 60 lemon saplings growing in CO₂-controlled rooms at the same greenhouse, under 400, 650, and 850 ppm [CO₂]. At each [CO₂] level, 10 saplings were exposed to 1-month dry-down after 2 months of standard irrigation, followed by re-watering for another month. The other 10 saplings served as controls. Under drought, tree growth was maintained at elevated, but not ambient, CO₂, linked with mild vs. severe tree water stress (leaf water potential of −3.5 at elevated and −5.5 MPa at ambient [CO₂]). Stomatal downregulation with increasing [CO₂] meant …