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- Author or Editor: D.S. de Villiers x
The effects of planting density and short-term changes in photoperiod on the growth and photosynthesis of bean (Phaseolus vulgaris L.) was investigated. Two cultivars of bean (cv. Etna, a dry bean variety; cv. Hystyle, a snap bean variety) were grown using nutrient film technique hydroponics in a walk-in growth chamber with a 12 h/12 h (light/dark) photoperiod and a corresponding thermoperiod of 28/24 °C (light/dark) and constant 65% relative humidity. Lighting for the chamber consisted of VHO fluorescent lamps and irradiance at canopy level was 400 μmol·m-2·s-1 PPF. For each cultivar, plants were grown at densities of 16 or 32 plants/m2. Short-term photoperiod changes were imposed during vegetative growth (21-29 DAP) and pod-fill (42-57 DAP). From the base 12 h/12h (light/dark) photoperiod, lighting in the chamber was cycled to provide 18 h/06 h (light/dark) or 24 h/0 h(continuous light) for 48 h. Diurnal single leaf net photosynthetic rates (Pn) and net assimilation vs. internal CO2 (Aci) measurements were taken during the short-term photoperiod adjustments. Results showed that there was no difference between cultivars or planting density with regard to total biomass or single leaf photosynthetic rates, but cv. Etna produced 35% more edible biomass than cv. Hystyle. Additionally, there was no effect of short-term photoperiod adjustment on single leaf Pn or Aci.
CO2 enrichment increases efficiency of light utilization and rate of growth, thereby reducing the need for supplemental lighting and potentially lowering cost of production. However, during warmer periods of the year, CO2 enrichment is only possible intermittently due to the need to vent for temperature control. Previous research investigated the separate and combined effects of daily light integral and continuous CO2 enrichment on biomass accumulation in lettuce. The current research was designed to look at the efficiency with which lettuce is able to utilize intermittent CO2 enrichment, test the accuracy with which growth can be predicted and controlled, and examine effects of varying CO2 enrichment and supplemental lighting on carbon assimilation and plant transpiration on a minute by minute basis. Experiments included application of various schedules of intermittent CO2 enrichment and gas exchange analysis to elucidate underlying physiological processes. Same-day and day-to-day adjustments in daily light integrals were made in response to occasional CO2 venting episodes, using an up-to-the-minute estimate of growth progress based on an integration of growth increments that were calculated from actual light levels and CO2 concentrations experienced by the plants. Results indicated lettuce integrates periods of intermittent CO2 enrichment well, achieving expected growth targets as measured by destructive sampling. The gas-exchange work quantified a pervasive impact of instantaneous light level and CO2 concentration on conductance and CO2 assimilation. Implications for when to apply supplemental lighting and CO2 enrichment to best advantage and methods for predicting and controlling growth under intermittent CO2 enrichment are discussed.