Effects Of Different Water And Light Treatments On The Eco-physiological Characteristics Of Amorpha Fruticosa Seedlings

Forest ecosystems suffer from severe destroy going with serious degradation of ecological functions just because of global climate changes as well as human disturbances at present. Restoring the increasing degraded ecosystems has become a hot point that is focused by many international orgnizations. Plants adapt to the changing environment through a variety of physiological and ecological characteristics. In recent years, more and more researches are focused on the relationship and basic mechanism between the plants and environment. It has become an important aspect of modern plant ecophysiological researches.In this study, we chose a common deciduous shrub-Amorpha fruticosa L. as the research object. We used modern ecophysiological equipments and measurements at Fanggan Ecological Experimental Station, in order to study the effects of different water and light treatments on the physiological and ecological characteristics of Amorpha fruticosa. The objective is to explore the water and light requirement disciplines of Amorpha fruticosa L. seedlings. The results will provide scientific basis and technical guidance for the scientific management of water and light factors of Amorpha fruticosa L. during its large-scale cultivation.Four different water supply levels were conducted by artificial water control in the rainout shelters, and two light levels were conducted in shade shelters covered by plastic films or woven black nylon nets. The growth, morphological architecture, photosynthetic characters, water use characteristic, biomass accumulation and allocation of one-year old Amorpha fruticosa L. seedlings responses to diverse water and light stresses were studied.The results showed that, with the increase in water stress under the same light level, morphological variables of height, stem diameter, crown area, total leaf number and total leaf area decreased. Leaf morphological parameters including leaf area, leaf mass became smaller with a short supply of water, the leaf became smaller, slimer and thicker. The content of light pigments showed significant differences, but there were no significant trends. Consistent with the increasing leaf water saturation deficit under water stress, net photosynthetic rate and transpiration rate decreased. Meanwhile, electron transport rate suffered serious inhibition, which also caused different ranges of decline of effective quantum yield, and photochemical quenching and non-photochemical quenching adjusted to consume excessive light, but photoinhibition still existed. Water use efficiency could be improved under moderate water stress. The decline of water lost rate under severe water stress indicated that the leaf moisture retaining power generally greater under severe water stress than that under well watered condition. Biomass accumulations to each organ were restricted by the deficit of soil water content. Under water stress, and biomass allocations were also affected, more photosynthetic products were transferred to belowground biomass, which caused increases of the root mass ratio as well as the root to shoot ratio.In the well watered conditions between different lights, light was the limiting factor for the growth of Amorpha fruticosa L. seedlings, and higher light intensity was necessary for photosynthetic accumulation. As a result, the morphological variables of height, stem diameter, crown area, total leaf number and total leaf area were all higher than those under shade. But in the severe water stresses, water became the lethal factor, the morphological parameters became higher under shade. The leaf morphological variables were also affected by light, and the leaves became bigger and thinner under shade. Net photosynthetic rate and transpiration rate were higher under stronger light intensity than that under shade, and furthermore, water use efficiency was improved as a result of greater increase of net photosynthetic rate than transpiration rate under stronger light intensity. Electron transport rate suffered serious inhibition under shade, while under stronger light intensity, Amorpha fruticosa L. seedlings expericened stronger and longer photoinhibition during the daytime. Under shade conditions, the contents of light pigments increased and Chl a/b decreased, which was useful for low-light capturing. Water saturation deficit decreased with the increase in relative water content under shade condition. Biomass accumulations to each organ and biomass allocations were all affected by light intensity, and moreover total biomass accumulations and biomass accumulations to each organ were restricted by shade. In seedlings under shade, more photosynthetic products were transferred to stems and leaves, which decreased the ratio of root to shoot.In conclusion, this research showed that the seedlings of Amorpha fruticosa L. can respond and adapt to environmental changes through various mechanisms, by which the seedlings can be assured to normally grow and survive under large-scale water and light stresses, and may adapt to more fluctuant climate changes in the future. All of these mechanisms make Amorpha fruticosa L. to be an ideal species for large-scale cultivation for its good adaptability, high ecological value and economic benefits.