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 (R90 B10 ) and a red/blue light ratio of 7:3 (R70 B30 ). 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.