The effect of red ∶ far red ratio on the stomata characters and stomata conductance of Chrysanthemum leaves
不同R∶FR值对菊花叶片气孔特征和气孔导度的影响

Chrysanthemum is among the four most important cut flowers in the world and is also China′s main export flower.To study the dynamic effects of different red(660±10) nm to far-red(730±10) nm radiation ratios on stomatal characteristics of greenhouse Chrysanthemum leaves,an experiment was carried out in the experimental greenhouse of Nanjing University of Information Science and Technology from October 2010 to February 2011.The greenhouse was 9.6 m wide and 30.0 m long,with top height and shoulder height being 5.0 m and 4.5 m,respectively.The experimental material was Chrysanthemum morifolium Ramat.cv.’Jingba’.Seedlings were transplanted on 6 October when they were about 20 cm in height and the number of leaves was 6—10.In the short-day trial stage,plants were irradiated for a total time of 10 hours(08:00-17:00) per day with one of four ratios of red light to far-red light(R ∶ FR).Those ratios were achieved using LED light sources and were 0.5,2.5,4.5,and 6.5,with a total light intensity of 1000 μmol · m-2 · s-1.A mixture of vermiculite and perlite with a volume ratio of 2 ∶ 1 was used as the culture substrate and the planting arrangement was 20 cm × 20 cm.All plants were irrigated with nutrient solution that had a conductivity of 1.5 ms/cm(200 μg/g N;80 μg/g P;170 μg/g K).During the vegetative growth phase,fluorescent lamps(PAR=200 μmol · m-2 · s-1) were used to supplement light for five hours(18:00—23:00) per day to extend the illumination time.The colorless nail polish imprint method was used to observe leaf epidermis stomatal characters under an optical microscope(Olympus CX-31),and a portable photosynthesis system(Li-6400) was used to measure leaf photosynthesis rate and stomatal conductance.The responses of the stomatal characters,stomatal conductance,and net photosynthesis rate of cut Chrysanthemum leaves subjected to different R ∶ FR ratios were studied.After 35 days of the short-day treatment,the maximum stomatal diameter of the upper epidermis and lower epidermis occurred at R ∶ FR ratios of 4.5 and 6.5,respectively,while the minimum diameters both occurred at R ∶ FR ratio of 2.5;the stomatal density and aperture reached maxima at R ∶ FR ratio of 2.5,while the minima occurred at R ∶ FR ratio of 6.5.Stomatal density and aperture on the lower epidermis were significantly higher than those on the upper epidermis.No significant differences in stomatal opening ratio and stomatal index were observed among different R ∶ FR treatments.With the same light intensity,stomatal conductance and photosynthesis rate were correlated to R ∶ FR ratio in the following descending order: 2.5,4.5,0.5,and 6.5.Leaf stomatal conductance was positively correlated with stomatal index,density,opening ratio,and aperture,while it was negatively correlated with stomatal length and breadth.Between 2.5 to 6.5 R ∶ FR ratio,leaf stomatal index,stomatal density,stomatal aperture,and stomatal conductance decreased significantly with an increase in the red light component.The