Effect of shading and air temperature on leaf photosynthesis, fluorescence and growth in lily plants

Abstract

Research was conducted in southern Italy to evaluate the physiological and productive responses of field-grown plants ( Lilium) in full light in comparison with the local practice of covering the crop with a shading net. Air and leaf temperature, leaf photosynthesis, leaf fluorescence, chlorophyll content, leaf area and plant dry matter were monitored during the crop cycle at different plant heights (apical, medial and basal parts). At harvest, flower quality production was slightly higher in sunlit plants, whereas dry matter accumulation did not differ between shaded and sunlit plants. During the growing season, leaves exposed to full sunlight showed slight reductions in fluorescence parameters without a parallel reduction in CER. Despite air temperature considered detrimental (over 30°C) and photon flux density (PFD) levels well above the light saturation point for this crop, lily plants showed good photosynthetic performance, supported both by high intrinsic efficiency of PSII photochemistry in darkness (ratio of variable to maximal fluorescence; F v/ F m) and good value of total chlorophyll without evident photoinhibition. No difference was detected among leaves at apical and medial positions, whereas basal leaves showed a progressive reduction of photosynthetic performance in sunlight, probably linked to high air temperatures near the ground. In sunlit conditions, although the temperature did not appreciably reduce the F v/ F m ratio, it was the main limiting factor of Lilium photosynthesis: while photosynthesis was almost zero at 37°C, the highest values were obtained at temperatures of 31–32°C with PFDs of 800 and 2000 μmol m −2 s −1. High light intensities are thus well tolerated by this crop. This is confirmed by the fact that apical leaves made a large contribution to total photosynthesis, even though they were exposed to higher PFDs. Our data confirm that Lilium shows good acclimation to high light conditions, although it is sensitive to high temperatures. As critical conditions occur infrequently during the plant crop cycle, shading may be restricted to the early vegetative growth phases after transplanting, when the plants are more sensitive to high temperatures. As shading reduces transpiration and soil evaporation, it may be used to reduce irrigation requirements of the crop.