Photosynthetic activity and yield of lettuce grown under shading

Abstract

Anexperiment was conducted to evaluate the effect of shading screens in relation to the full sun on the photosynthetic capacity and productivity of Elbe crested lettuce in the climatic conditions of Santarém -PA. The experimental design was completely randomized blocks with four replicates. Two types of shading and one plastic (50% green screen, 50% black screen and 150μm transparent plastic) were studied in addition to the control (full sun). The height, diameter, number of leaves and weight of a plant, yield, leaf mass ratio (RMF) and stem ratio (RMC) were evaluated, as well as the net carbon assimilation rate (A), stomatal conductance to steam Water (gs), transpiration rate (E), instantaneous water use efficiency (A/E) and relation between internal and external carbon concentrations (Ci/Ca). The green screen and the plastic provided a productivity gain (49.26% and 48.47%, respectively, in relation to the cultivation in full sun) due to the greater number of leaves, weight of a plant and allocation of drymass to the sheets. The photosynthetic rate and the water use efficiency increased 24.1% and 21.94%, respectively, with the use of plastic in relation to the conduction in full sun. Under the transparent plastic, greater stomatal conductance, CO2concentration, photosynthetic rate, better water use efficiency and greater dry mass accumulation occurred. The yield increases for lettuce grown under the shade screens were due to increases in the photosynthetic activity of the plants.