Red/blue light ratio strongly affects steady‐state photosynthesis, but hardly affects photosynthetic induction in tomato ( Solanum lycopersicum )

Plants are often subjected to rapidly alternating light intensity and quality. While both short‐ and long‐term changes in red and blue light affect leaf photosynthesis, their impact on dynamic photosynthesis is not well documented. It was tested how dynamic and steady‐state photosynthetic traits were affected by red/blue ratios, either during growth or during measurements, in tomato leaves. Four red/blue ratios were used: monochromatic red (R100), monochromatic blue (B100), a red/blue light ratio of 9:1 (R90B10) and a red/blue light ratio of 7:3 (R70B30). R100 grown leaves showed decreased photosynthetic capacity (maximum rates of light‐saturated photosynthesis, carboxylation, electron transport and triose phosphate use), leaf thickness and nitrogen concentrations. Acclimation to various red/blue ratios had limited effects on photosynthetic induction in dark‐adapted leaves. B100‐grown leaves had a approximately 15% larger initial NPQ transient than the other treatments, which may be beneficial for photoprotection under fluctuating light. B100‐grown leaves also showed faster stomatal closure when exposed to low light intensity, which likely resulted from smaller stomata and higher stomatal density. When measured under different red/blue ratios, stomatal opening rate and photosynthetic induction rate were hardly accelerated by increased fractions of blue light in both growth chamber‐grown leaves and greenhouse‐grown leaves. However, steady‐state photosynthesis rate 30 min after photosynthetic induction was strongly reduced in leaves exposed to B100 during the measurement. We conclude that varying red/blue light ratios during growth and measurement strongly affects steady‐state photosynthesis, but has limited effects on photosynthetic induction rate.