Stomatal anatomy and closing ability is affected by supplementary light intensity in rose (Rosa hybrida L.)

Increasing the light level in protected cultivation of ornamental crops via supplementary lighting is critical to enhance both production and external quality especially during the periods of low light availability. Despite wide applications the effects of light intensities were not previously addressed on water loss pathways. In this study rose plants were cultivated at 100, 200 or 400 μmol/(m2.s) photosynthetic photon flux density (PPFD). The stomatal responsiveness to desiccation, stomatal anatomical features and cuticular transpiration were determined. Plant biomass as well as photosynthesis response to light and CO2 were also assessed. Increasing growth PPFD led to a considerable increase in plant biomass (85 and 57% for 100 to 200 and 200 to 400 μmol/(m2.s) respectively). Photosynthesis was marginally affected by increasing growth PPFD from 100 to 200 μmol/(m2.s) while a further rise to 400 μmol/(m2.s) considerably increased photosynthetic rate at high light intensities. Higher PPFD during cultivation generally led to larger stomata with bigger pores. A PPFD increase from 100 to 200 μmol/(m2.s) had a small negative effect on stomatal closing ability whereas a further rise to 400 μmol/(m2.s) had a substantial stimulatory effect. Cultivation at a PPFD higher than 100 μmol/(m2.s) led to lower rates of cuticular transpiration. In conclusion, high growth PPFD (> 200 μmol/(m2.s)) enchanced both photosynthetic and stomatal anatomical traits. High light intensity (> 200 μmol/(m2.s)) also led to a better control of water loss due to more responsive stomata and decreased cuticular permeability.