EFFECT OF SHADING AND AIR-TEMPERATURE ON LEAF PHOTOSYNTHESIS, FLUORESCENCE AND GROWTH IN LILY PLANTS

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 sha ding net. Air and leaf temperature, leaf photosynthesis, leaf fluoresc ence, chlorophyll content, leaf area and plant dry matter were monitor ed during the crop cycle at different plant heights (apical, medial an d basal parts), At harvest, flower quality production was slightly hig her in sunlit plants, whereas dry matter accumulation did not differ b etween shaded and sunlit plants. During the growing season, leaves exp osed to full sunlight showed slight reductions in fluorescence paramet ers without a parallel reduction in CER, Despite air temperature consi dered detrimental (over 30 degrees C) and photon flux density (PFD) le vels well above the light saturation point for this crop, lily plants showed good photosynthetic performance, supported both by high intrins ic efficiency of PSII photochemistry in darkness (ratio of variable to maximal fluorescence; F-v/F-m) and good value of total chlorophyll wi thout evident photoinhibition. No difference was detected among leaves at apical and medial positions, whereas basal leaves showed a progres sive reduction of photosynthetic performance in sunlight, probably lin ked to high air temperatures near the ground. In sunlit conditions, al though the temperature did not appreciably reduce the F-v/F-m ratio, i t was the main limiting factor of Lilium photosynthesis: while photosy nthesis was almost zero at 37 degrees C. the highest values were obtai ned at temperatures of 31-32 degrees C with PFDs of 800 and 2000 mu mo l m(-2) s(-1). High light intensities an thus well tolerated by this c rop. This is confirmed by the fact that apical leaves made a large con tribution to total photosynthesis, even though they were exposed to hi gher PFDs. Our data confirm that Lilium shows good acclimation to high light conditions, although it is sensitive to high temperatures. As c ritical conditions occur infrequently during the plant crop cycle, sha ding may be restricted to the early vegetative growth phases after tra nsplanting, when the plants are more sensitive to high temperatures. A s shading reduces transpiration and soil evaporation. it may be used t o reduce irrigation requirements of the crop. (C) 1997 Elsevier Scienc e B.V.