Resumo -Foram avaliadas as respostas das trocas gasosas à irradiância, à temperatura, ao déficit de pressão de vapor e à concentração interna de CO 2 em plantas jovens de laranjeira 'Valência', tangor 'Murcote' e lima ácida 'Tahiti', sob condições controladas. As taxas máximas de assimilação de CO 2 foram de 9,8, 12,8 Photosynthetic responses of three citrus species to environmental factorsAbstract -Gas exchange responses to irradiance, temperature, air vapor pressure deficit and intercellular CO 2 concentration were evaluated in young plants of sweet orange 'Valência', tangor 'Murcote' and acid lime 'Tahiti' plants, under controlled conditions. Maximum rates of CO 2 assimilation were around 9.8, 12.8 and 13.0 µmol m -2 s -1 , respectively, for 'Valência', 'Murcote' and 'Tahiti', and these differences were related to stomatal conductance and instantaneous carboxylation efficiency. Light saturation of photosynthesis was around 750 µmol m -2 s -1 for 'Valência', whereas 'Murcote' and 'Tahiti' did not show evident light saturation, exhibiting small increases of CO 2 assimilation above 1,000 µmol m -2 s -1 . The CO 2 compensation point was 4.8, 5.8 and 5.4 Pa for 'Valência', 'Murcote' and 'Tahiti', respectively, indicating differences in photorespiration of these citrus species. Leaf temperatures between 25 o C and 30 o C were optimum for photosynthesis of 'Valência', whereas this optimum was around 30 o C for 'Murcote' and 'Tahiti'. At temperatures above or below the optimum range, CO 2 assimilation was reduced by partial decrease of stomatal conductance and instantaneous carboxylation efficiency. Reduced CO 2 assimilation rate was also caused by increasing vapor pressure deficit from 1.5 to 3.5 kPa, and this effect enhanced when temperature increased from 28 o C to 35 o C.
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