CO2 assimilation in lettuce plants under photoselective plastic greenhouse films

The effect of greenhouse films with photochromatic additives on CO2 assimilation by lettuce plants was studied. These films showed differences in transmittance and radiation spectral balance. The polyethylene films showed less transmittance and spectral bias to red in contrast with polypropylene films with more transmittance and bias to the blue spectral region. CO2 assimilation did not correlate with irradiance under the Films but correlated with the spectral balance. The enrichment with red was positive for CO2 assimilation; enrichment with blue showed the opposite effect. The best results were obtained with a mixture of green and blue photochromatic additives (0.5%) in polyethylene film. On the other hand, CO2 assimilation under polypropylene film was not modified significantly by photochromatic additives. Stomatal activity and leaf temperature did not show correlation with radiation characteristics under the films.