The Physiological And Biochemical Characteristics Of The Water Hyacinth(Eichhornia Crassipes) In Adapting Different Growth Conditions

Eichhornia crassipes (Mart.) Solms (Pontederiaceae), also known as water hyacinth, is a perennial erect herb native to South America. It was introduced to China as aquatic feed originally and then naturalized in wild gradually. E. crassipes has become one of the top ten invasive plants widely distributing in 18 regions in southeast China (province, city and municipality) , including Zhejiang, Shanghai, Fujian, and Yunnan. Accordingly, it is very important to elucidate the mechanisms of biological invasion of E. crassipes for the integrated control and utilization of this species. In this study, we selected E. crassipes collected from Shuikou power station of Min River as experimental materials and studied the effects of nutrient level, and heavy metal stress of cadmium on growth dynamics, tillering dynamics, morphological characteristics, physiological and biochemical characteristics, endogenous hormones and rhizosphere microbial community functional diversity of the plant through field survey and indoor simulation experiments. The main results are as follows:(1) By cultivating E. crassipes in an eutrophic inner river for a interval of 210 days, the plant showed its strong asexual reproductive ability. The fresh weight and tiller number significantly increased from May to July, the relative growth rate of fresh weight was up to 9.42 times and the relative tiller number reached 3.67 times. The growth of the plant slowed down significantly from August and there was no significant fresh weight increase from late October to late November. The maximum density of E. crassipes in nutrient-rich river was about 55.7 kg/m² and the density of tiller number was about 133/m².(2) The results of indoor simulation experiments of culturing E. crassipes in the hydroponic solution, which the concentration of the nutrients was 0.01, 0.025, 0.05, 0.2, 1, 5, 10 times as higher as that of Hoagland hydroponic solution. The results showed that E. crassipes grew best in 1 time Hoagland nutrient solutions and the relative growth rate of it was up to 22 times, within 120 days. By culturing E. crassipes in nutrient solutions lack of N, P, E. crassipes performed with more shorter height, longer lateral roots, thinner and smaller leaves .There is significant impact on the growth of E. crassipes under the N deficit condition. The tiller number was only 47.1% as many as that of control and 50.0% of which lacking of P, and fresh weight is 38.7% and 44.3% respectively. In addition, when E. crassipes was cultured in the solutions containing nitrogen 30.0 mg/L, 15.0 mg/L, 7.5 mg/L and 3.75 mg/L for 125 days, respectively, the fresh weight of E. crassipes increased to 20.5, 32.1, 14.9 and 10.2 times as that of beginning. and the highest biomass was found in the 15.0 mg/L nitrogen condition(3) Laboratory experiments of culturing E. crassipes in Hoagland solutions containing 0 mg/L, 1 mg/L, 5 mg/L and 10 mg/L Cd2 + showed that the cadmium accumulation index of E. crassipes was up to 448 by treating the plant for 30 days in 5 mg/L Cd²⁺solution, and Cadmium mainly accumulated in roots,the accumulation of Cd was positive related to the concentration of Cd²⁺ treated. Under 10 mg/L Cd²⁺solution, the content of cadmium in roots was 2741.3 mg/kg, which was 20.7 times as higher of that in the stems and leaves. Furthermore, physiological and biochemical analysis indicated that the content of soluble protein and protection enzyme system activity significantly increased in leaves and roots of E. crassipes under cadmium stress, showing soluble protein content in leaves was about 1.5～1.8 times as higher as that in roots, MDA content in leaves of E. crassipes had no significant changes, MDA content in roots significantly increased after 20 days treatments by 10 mg/L Cd²⁺, so the earlier and severe damage of cadmium to roots than to leaves was recorded. Under the condition of cadmium stress, IAA, GA and ZR contents increased initially and decreased latter, all of them increased under 5 mg/L Cd²⁺ while significantly reduced under 10 mg/L Cd²⁺ conditions. Endogenous hormone ABA content was positive correlated with cadmium concentration, it was 135.33 ng/g·FW under 10 mg/L Cd²⁺, which was 2 times as higher as that of control. The co-regulation among IAA, ZR and GA respond for the higher resistance of E. crassipes to cadmium stress.(4) Under the condition of cadmium stress, the population density of microorganisms in the rhizosphere of E. crassipes reduced with the increasing of cadmium concentration. but no significant difference was found between CK and 1mg/L Cd²⁺ treatment. But the population density of microbet was only 67%of CK under 10 mg/L Cd2 +treatment. The analysis of components of the microbe in the rhizospheric soils showed that population density of Azotobacteria, Nitrobacteria and Ntrosobacteri reduced with the increasing of cadmium concentration. There was significantly change found under 10 mg/L Cd²⁺ , nitrification bacteria population density reduced to 45% of that in CK. The population density of denitrifying bacteria increased under low cadmium stress, while decreased under high cadmium concentration. Similar trend was found in ammonification and aerobic cellulose decomposing bacteria. Biological community functional diversity of rhizospheric microbe, which was analysed by BIOLOG method, showed higher utilization ability of organic compounds under 0 mg/L and 1mg/L Cd²⁺ environments than under 5 mg/L or 10 mg/L Cd²⁺ conditions, by rhizospheric microorganisms of E. crassipesIn summary, E. crassipes has stronger asexual reproductive ability, higher plasticity, together with the changing of protection enzymes system and hormones, which resulting in higher resistance to stressful environment. The changing diversity of rhizospheric microbe also played an important role in maintaining the cycling of nutrient, restoring eutrophication and cadmium-containing water area, indicating a strong growth adaptability of E. crassipes as well.