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Rising atmospheric CO₂ stimulates photosynthesis and productivity of forests, offsetting CO₂ emissions^,. Elevated CO₂ experiments in temperate planted forests yielded ∼23% increases in productivity over the initial years. Whether similar CO₂ stimulation occurs in mature evergreen broadleaved forests on low-phosphorus (P) soils is unknown, largely due to lack of experimental evidence. This knowledge gap creates major uncertainties in future climate projections^, as a large part of the tropics is P-limited. Here, we increased atmospheric CO₂ concentration in a mature broadleaved evergreen eucalypt forest for three years, in the first large-scale experiment on a P-limited site. We show that tree growth and other aboveground productivity components did not significantly increase in response to elevated CO₂ in three years, despite a sustained 19% increase in leaf photosynthesis. Moreover, tree growth in ambient …