Physiological And Ecological Responses Of Urban Ornamental Plants To Night Illumination

Landscape plant is an important part in the urban ecosystem, and plays important roles in beautifying urban environment, cleaning the air and maintaining urban ecosystem balance. At present, the urban ecological environment has been seriously threatened, and landscape plants are also suffering from many kinds of environment stresses, such as high temperature, low temperature, drought, water pollution, air pollution, solid waste pollution, noise pollution and a new light pollution. Light pollution may give different effects on plant growth and reproduction, but little information has been available on the physiological and ecological responses of urban ornamental plants to artificial night illumination in urban. Based on the scientific hypothesis that "night light may have some physiological and ecological effects on plant growth and phenology", therefore, a night illumination experiment was carried out to study the responses of Impatiens gardenia, and Chrysanthemum to 4-h and 8-h night illumination. After one growing season, plant biomass accumulation, concentrations of carbon, nitrogen, phosphorus and photosynthetic pigment, and enzyme activity under night illumination were measured. Meanwhile, the phenology was also observed.(1) There were different effects on biomass accumulation and allocation among three kinds of plant due to night illumination:night illumination has a significant effect on Impatiens leaf biomass, stem biomass, above-ground biomass and total biomass. In the condition of night lighting from 18:00 to 8:00 of the next day (treatment A), Impatiens tends to allocate more biomass to leaf and stem, so as to increase Impatiens above-ground biomass and total biomass. In the condition of night lighting from 18:00 to 24:00(treatment B), the leaf dry matter accumulation is also significantly increased. Night illumination reduced the number and weight of Gardenia flower, but there is no significant impact on leaf and stem biomass, flower, total weight of above-ground part, root biomass, and total biomass. Night illumination only increased biomass of Chrysanthemum stems and reduced the number of flowers. There was little effect on leaf biomass, flower weight, average flower weight, above-ground biomass, root biomass and total biomass. But the effects of night illumination on three species still have similarities. Night illumination affected the normal day-night cycle, and reduced the number of plant flowers blossom and flower average weight at the stage of reproductive growth. In the vegetative growth stage, night illumination induced an increase in photosynthetic to synthesize more organic matter, so as to promote the accumulation in plant leaf and stem biomass.(2) Night illumination had seriously affected the blossom time of Impatiens, and the night illumination caused Impatiens no flowering during the treatment.18:00-24:00 night illumination made the Impatiens a delay of 97 days to flower, but there is no significant effect on Impatiens blossom time--both were about 30 days. The effect of night illumination on Gardenia was different. Neither of the initial flowering time and flower blossom time have been affected significantly, but the night light significantly reduced the number of Gardenia flowers. The night illumination affected the Chrysanthemum obviously. A and B treatments significantly affected the Chrysanthemum blossom, only producing buds but no blossoming.(3) On the condition of lighting from 18:00 to 8:00 of the next day, chlorophyll a, chlorophyll b and carotenoids of Impatiens decreased significantly. In contrast, on the condition of lighting from 18:00 to 24:00, chlorophyll a/b of Impatiens increased and chlorophyll (a+b) decreased. On the condition of lighting form 18:00 to 8:00 of the next day chlorophyll a, chlorophyll b, total chlorophyll content of Gardenia significantly decreased, but chlorophyll Caro/(a+b) and a/b increased significantly. Chrysanthemum leaf pigment was not sensitive to the night illumination, except for an increase in chlorophyll a/b in the treatment B.(4) In the condition of night illumination, the Impatiens Carbon content of stem and root reduced, Gardenia leaf carbon content reduced, and Chrysanthemum Carbon content of leaf reduced, while flower carbon increased. Night illumination caused a decrease in Nitrogen content in leaf and stem of Impatiens, and Gardenia Nitrogen content in stem and flower to also reduced. But there was little effect on nitrogen content in other parts of Chrysanthemum. In the case of Phosphorus, night illumination caused a decrease in Phosphorus content in Impatiens leaf, as well as it in root and flower of Gardenia and in leaf and root of Chrysanthemum. This indicated that the night illumination limits uptake of nutrients in the plants, and to some extent it affects the distribution of Carbon, Nitrogen and Phosphorus(5) The SOD, POD activity of Impatiens significantly increased when exposed to the night lighting, but there was no significant difference in MDA content. In Gardenia, above enzymes-SOD and POD firstly increased and then decreased with the increase in the time of night illumination, and the content of MDA increased significantly. In Chrysanthemum, MDA and activities of two above enzymes did not change significantly when exposed to the night illumination.In a word, the change in light environment caused by night illumination has a certain impact on plant physiology and ecology, which are different on various species. Night illumination breaks the balance of plant biomass allocation, and undermines the nutrient distribution equilibrium, as well as disturbs plant blossom, synthesis of photosynthetic pigments, and plant enzyme activities.