Stomatal limitation of photosynthesis in winter production of greenhouse tomato plants

Abstract

In May, greenhouse tomato (Lycopersicon esculentum Mill.) plants near the end of their winter production cycle were shown to exhibit a diurnal photosynthetic decrease. In order to identify the physiological causes of this decline, we compared in May the photosynthetic characteristics of the fifth youngest leaves from tomato plants of different ages corresponding to a winter production (11-month-old plants) and to a spring production (5-month-old plants). Although the leaves were developed simultaneously under the same environmental conditions, only the ones from the winter production showed a diurnal decline of the in situ CO2 assimilation rate (ACO2). This was accompanied by a decline of internal CO2 and stomatal conductance and by large accumulations of hexoses. When stomatal closure was relieved under saturated CO2 concentration (5%) using a leaf-disc electrode system, the fifth leaves of both tomato cultures had similar maximum quantum efficiency of O2 evolution (Φmax), light-saturated rate of O2 evolution (Pmax) and quantum efficiency of photosystem II (PSII) photochemistry (ΔF/F′m, qP and qN). We concluded that the diurnal decline of ACO2 observed in winter tomato production during May originates from a stomatal limitation that is not dependent on environmental conditions but rather related to the developmental stage of the plants.