Responses of strawberry leaf photosynthesis, chlorophyll fluorescence and macronutrient contents to elevated CO2

Gas exchange, chlorophyll fluorescence parameters, and macronutrient contents were investigated in young (< 3 weeks), medium (4 - 6 weeks) and old (7 - 9 weeks) strawberry leaves growing at 300, 450, 600, 750, and 300 ppm CO2. An increase of the CO2 level to 600 ppm promoted leaf net photosynthesis, but a further rise led to a decrease of net CO2 assimilation. The reduction of net photosynthetic rate was less distinct in young leaves exposed to CO2 levels above 600 ppm for less than 3 weeks, indicating that the reduction might depend on the period of exposition or leaf age. Transpiration and stomatal conductance were significantly affected by leaf age, but not by CO2 concentrations. Medium leaves were characterised by a higher transpiration rate and stomatal conductance than young and old ones. In leaves growing at high CO2 levels Chl a and b contents as well as the a/b ratio decreased. The contents of N, P, K, Ca and Mg were lower in leaves growing at high CO2 concentrations than in those at low ones. An elevated CO2 level above 750 ppm led to a general macronutrient deficiency and was accompanied by a distinct decrease of optimal quantum yield, due to a rise of basal fluorescence, and an increase of non-photochemical energy dissipation in old leaves.