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Accumulated carbon uptake, apparent quantum yield (AQY) and light-saturated net CO₂ assimilation (A_sat) were used to assess the responses of photosynthesis to environmental conditions during spring for three consecutive years. Whole-tree chambers were used to expose 40-year-old field-grown Norway spruce trees in northern Sweden to an elevated atmospheric CO₂ concentration, [CO₂], of 700 μmol CO₂ mol⁻¹ (C_E) and an air temperature (T) between 2.8 and 5.6 °C above ambient T (T_E), during summer and winter. Net shoot CO₂ exchange (A_net) was measured continuously on 1-year-old shoots and was used to calculate the accumulated carbon uptake and daily A_sat and AQY. The accumulated carbon uptake, from 1 March to 30 June, was stimulated by 33, 44 and 61% when trees were exposed to C_E, T_E, and C_E and T_E combined, respectively. Air temperature strongly influenced the timing …