Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

Abstract

The rate of net photosynthesis (P) of whole plant stands of tomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativus L.) and sweet pepper (Capsicum annuum L.) was measured in six long-term experiments in large greenhouses under normal operating conditions and CO2-concentrations between 200 and 1200 μmol mol-1. The objective was to quantify the responses to light and carbon dioxide and to obtain data sets for testing simulation models. The method of measuring canopy photosynthesis involved an accurate estimation of the greenhouse CO2 balance, using nitrous oxide (N2O) as tracer gas to determine, on-line, the exchange rate between greenhouse and outside air. The estimated relative error in the observed P was about ± 10%, except that higher relative errors could occur under particular conditions.A regression equation relating P to the photosynthetically active radiation, the CO2 concentration and the leaf area index explained 83-91% of the variance. The main canopy photosynthesis characteristics calculated with the fitted regression equations were: canopy Pmax 5-9 g m-2 h-1 CO2 uptake; ratio Pmax/LAI 1·5-3 g m-2 h-1; light compensation point 32-86 μmol s-1 m-2; light use efficiency (quantum yield) at low light 0·06-0·10 μmol μmol-1 and CO2 compensation point 18-54 μmol mol-1. The results were related to the prevailing conditions.