| The genus Hosta is herbaceous perennials belonging to the family Liliaceae. Hosta plants are extremely popular owing to their varieties of leaf types, leaf shape and plant types, which have developed into important shade-tolerant field perennial flowers in northern China. With the rapid economic development and urbanization gradually accelerated in China, the market demand of Hosta plants is increasing year by year. However, the use of Hosta germplasm resources is greatly restricted due to little early investment in science and technology and lack of systematic research.Nowdays Hosta plantaginea and Hosta ventricosa are still the main Hosta plants in landscaping. The studies on introduction and cultivation of Hosta plants have got some preliminary results, but are still at the exploratory stage. On the other hand, the study on effects of cultivation conditions (light, fertilizer, water, etc.) on the growth and ornamental traits of Hosta plant has just started, which difficultly meets the scientific and technological demands ahout germplasm conservations as well as the new superior germplasm large-scale production and cultivation of Hosta plant.The study focused on the main cultivation conditions (light, fertilizer, water) impacting the growth and ornamental characteristics of Hosta plants to explore the effects of nitrogen fertilizer on leaf color of a chimera Hosta, interactive effects of light intensity and controlled release nitrogen fertilizer supply on photosynthesis of Hosta Tratt., as well as effects of drought stress and rewatering in subjecting to water stress on the growth and photosynthesis of Hosta Tratt. The aims of this work were:(1) to ascertain (i)the effects of light intensity and controlled release nitrogen fertilizer supply on photosynthesis and growth of Hosta during different growth stages;(ii) whether stoloniferous rootstock of Hosta affect plant nitrogen requirements and the adaptability to light;(iii)whether the interactive effects of both factors exist.lt could provide a theoretical support for further study on shade tolerance mechanisms of the Hosta plants, as well as guide CRNF application in Hosta cultivation.(2) to determine the effects of drought stress and rewatering in subjecting to water stress on the growth and photosynthesis of Hosta Tratt., which provides theoretical basis for improving water use efficiency Hosta plant and implementing water-saving cultivation.(3) to elucidate the internal mechanism that excessive application of nitrogen fertilizer could result in leaf colors’ dramatic changes of an unstable chimera type of Hosta, in order to provide necessary scientific basis for the cultivation application and artificial regulation on ornamental characteristics of those types of Hosta varieties. The results showed:The interactive effects of light intensity and controlled-release nitrogen fertilizer (CRNF) supply on growth, gas exchange, and chlorophyll (Chi) fluorescence parameters of two species of potted Hosta seedlings, original species of the genus Hosta in China, were studied. N4(4g of CRNF per pot), N8(8g of CRNF per pot), and sometimes N12(12g of CRNF per pot), significantly increased total dry weights, net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), the maximum quantum yield of PSⅡ photochemistry (Fv/Fm), the maximum ratio of quantum yields of photochemical and concurrent nonphotochemical processes in PSⅡ (Fv/Fo), actual efficiency of photochemical energy conversion in PSⅡ under light (ΦPSⅡ), and photochemical quenching coefficient (qP), but significantly decreased internal CO2concentration (Ci) and nonphotochemical Chi fluorescence quenching (NPQ) compared to control plants at different growth stage of the two Hosta species in two levels of light intensities (50%of natural light (L50) and70%of natural light (L70)). Based on the available data, we concluded that the increments in total dry weights of Hosta clausa var. ensata and Hosta ventricosa by appropriate amount of CRNF supply treatments under L50and/or L70light conditions are directly related to the increments in the PN, which may be due to both stomatal and nonstomatal improvements for a longer growing time. Furthermore, there was an interaction between light intensity and CRNF supply treatments on growth and photosynthetic characteristics of the two Hosta species. The adaptability of Hosta plants with obvious stoloniferous rootstock to stronger light was higher than that of Hosta plants without obvious stoloniferous rootstock.Hosta clausa var. ensata and Hosta ventricosa which were two original species of the genus Hosta in China was used as materials to study the effects of drought stress and rewatering in subjecting to water stress on the plants’ dry weights, some morphological indicators, chlorophyll content, gas exchange and chlorophyll fluorescence parameters. The results showed that:with the extension of drought stress time and the increase of aridity, the inhibition of drought stress on dry weights, some morphological indicators and chlorophyll content of two kinds of Hosta plants gradually increasesd. In addition, drought stress could reduce or significantly reduce the net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), decrease or increase internal CO2concentration (Ci), and reduce or significantly reduce the maximum quantum yield of PSⅡ photochemistry (Fv/Fm), the PSⅡ maximum efficiency within light-adapted material (Fv’/Fm’), actual efficiency of photochemical energy conversion in PSⅡ under light (ΦPSⅡ), photochemical quenching coefficient (qP), but significantly enhance the nonphotochemical Chi fluorescence quenching (NPQ) of the two kinds of Hosta plants.While rewatering for15d after drought stress for15d or30d could restore or partially restore the losses caused by drought, and drought stress for30d didn’t cause irreversible damage to the photosynthetic organelles. The drought resistance of Hosta clausa var. ensata was stronger than Hosta ventricosa.Leaf color was studied in excessive application of nitrogen fertilizer cultivation on chimera Hosta ’Gold standard’. The results showed that:chlorophyll content significantly increased or decreased in yellow or green leaf area of the chimera in the2g·kg-1of urea fertilizer treatment respectively, and leaf of chimera completely turned green within28d. Total N content, activities of nitrate reductase (NR) and glutamate dehydrogenase (GDH) of chimera leaf reached to their highest level after7days treatment; activities of glutamine synthetase (GS) reached to their highest level after14days treatment, and the changing trends of glutamate synthetase (GOGAT) activities was similar to chlorophyll content on chimera leaf. The develepoment of chloroplast ultrastructure, which lacks normal grana stacking, and contains large number of vacuoles was severely inhibited in the yellow leaf area of the chemera. After28d-fertilization treatments, normal thylakoid lamellar structure was formed in chloroplast of yellow leaf area, which was similar to the chloroplast structure of the green leaf area.These results will provide necessary theoretical supports for the key technical protocol development of suitable supporting cultivations, seed production and application on Hosta shade-tolerant open perennial ornamental flowers, as well as be of great significance to improve China’s garden applications and germplasm innovation capability of Hosta plants and enhance the international competitiveness of the garden plants industry. |
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