| Water is one of the main environmental factors affecting plant growth. In recent years, with the global climate warming, the shortage of water resources is increasingly serious in our country, especially in Northeastern China. Water stress has become an important ecological problem of reducing plant growth and development in Northeastern China. Miscanthus sacchariflorus and Miscanthus sinensis are the ideal second generation of energy plants, and have wide application value, but a lack of water resources restricts the promotion and application of Miscanthus in the Northeast of China. Therefore it is great significance to study on growth, photosynthetic characteristics and physiological characteristics of M. sinensis and M. sacchariflorus under water stress for improving its moisture management level, promoting Miscanthus sinensis and Miscanthus sacchariflorus in the Northeastern region’s sustainable development.The characteristics of seed germination under different PEG stress (5%,10%,15%,20%) were studied taking the selected M. sinensis and M. sacchariflorus as experimental materials. For the purpose of studying the adaptability to natural soil water stress, the photosynthetic characteristics, physiological and biological index were measured under4treatments, normal water (soil moisture content for the maximum80%field capacity, the same below), mild soil drought stress (65%), moderate soil drought stress (50%) and severe soil drought stress (35%).Meanwhile the distribution and habitat characteristics of M. sacchariflorus and M. sinensis in northeastern China were investigated. The main research results are as follows.(1) Miscanthus in the northeast China is dotted and prefer the habitat of low altitude, soil moisture and high light intensity. There were differences of Miscanthus growth traits under different habitats, and the growth potential and biomass increased with the soil water content increasing and light conditions improving. There was a significant difference of some growth traits among different habitats (P<0.05). The coefficient of Variance in Miscanthus the growth traits, leaf shape index, plant height、stem diameter and depth of underground distribution of phenotypic traits were relatively stable, and were less influenced by environmental factors. The plant height and stem diameter were significantly related to plant biomass by using principal component analysis.(2)There is no significant effect of lower concentration PEG (5-10%) on the seeds’ germination rate of M.sinensis and M. sacchariflorus. But it increased the germination index, vigor index, radicle length, radicle fresh weight of M. sinensis and plumules growth of M. sacchariflorus. The higher PEG concentration(15-20%) inhibited significantly the growth of seed, and the germination rate termination index, vigor index and radicles/plumule were reduced. The half of lethal concentration of M. sacchariflorus was15%, and the lethal concentration of M. sacchariflorus was20%. However, the half of lethal concentration of M. sinensis was15%, the lethal concentration of M. sinensis was higher than20%.(3)Under soil drought stress, leaf relative water content (RWC), chlorophyll (Chl)contentnet, photosynthetic rate (Pn), maximum net photosynthetic rate(Pmax), apparent quantum efficiency (AQE), dark respiration rate (Rd), light saturation point (LSP),transpiration rate (Tr), maximum carboxylation rate (Vcmax) and the maximum electron transport rate (Jmax) reduced, while light compensation point (LCP) and water use efficiency (WUE)increased along with the soil drought stress degree enhancing.The stomatal conductance (Gs) of M. sinensis and M. sacchariflorus decreased with soil drought stress degree enhancing. The intercellular CO2concentration (Ci) decreased firstly and then increased, while stomatal resistance value (Ls) increased firstly and then decreased.The photosynthesis inhibition of M. sacchariflorus under mild soil drought stress and M. sinensis under mild and moderate soil drought stress were caused by the stomatal limitation; while the photosynthesis inhibition of M. sacchariflorus under moderate and severe soil drought stress and M. sinensis under serious soil drought stress were caused by non-stomatal limitation.(4)Under soil drought stress, cell membrane relative permeability, the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) increased significantly with soil drought stress degree enhancing.Under mild drought stress, the superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity of M. sacchariflorus increased gradually along with soil drought stress proceeding; under moderate and severe drought stress, the SOD, CAT and POD activity increased firstly and then decreased; SOD and CAT activity of M. sinensis increased gradually along with soil drought stress proceeding; While there is no obvious change of the POD activity under different treatments.Under soil drought stress, there are rising trend of the value of ascorbic acid peroxidase (APX) activity, leaf glutathione reductase (GR) activity, ascorbic acid (AsA) content and reduced glutathione (GSH) content of M. sinensis. Under mild drought stress M. saccharifloru also could maintain high ascorbic acid synthesis and metabolic activity, but under the moderate and severe drought stress, with the intensification of soil drought stress, APX, GR activity and GSH, AsA content began to decrease.(5) Under soil drought stress, the plant height, ground diameter, stem internode length, leaf area, specific leaf weight decreased along with the soil drought stress degree enhancing. Under mild drought stress, rhizome stem diameter and length of M. sinensis were higher than normal, which showed that suitable soil drought stress on M. sinensis could promote rhizome growth. However under the moderate and severe drought stress, rhizome stem diameter, length and number of tillers decreased significantly as the soil drought stress degree intensified.Under soil drought stress, the per plant total biomass, the biomass on the ground, underground biomass and crown root ratio decreased with soil drought stress degree intensifying except of the increase of the underground biomass under mild drought stress.The heavier stress, the slower the growth rate, the smaller the increment and lower biomass. |
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