Invasion Mechanism Of Alien Plant-Conyza Canadensis L.

Conyza canadensis L., originally found in North America, has become a worldwide weed, and has widespread in many regions of China.This weed has threatened the biodiversity and damaged the ecological envRIonment. Guided with the principle of "Integrated pest management", this research mainly studied the invasive mechanism of alien plant-Conyza canadensis, and explored the comprehensive treatment Program.With its invasion biology, physiology, physiological ecology and physical chemistry as the main line,the research conducted four parts.the growth habits and component biomass allocation of Conyza canadensis were studied, on the basis of the correlation analysis between its biological characteristics and effective accumulated temperature, understanding its photosynthetic matter accumulation and nutrition distribution proportion;and then, with the drought-resistant mechanism as the breakthrough point, some physiological indexes,such as water content, chlorophyll, MDA, proline and peroxidase system were measured, aimed to analyze the physiological mechanism of distribution of worldfield; Further under the conditions of natural light and artificial light, CO2 concentration, determined the net photosynthetic rate, transpRIation rate and water use efficiency, and analyzed the correlation with ecological factors, its invasion mechanism from the aspects of dry matter accumulation rate were explored; By means of drilling down allelopathy of Conyza canadensis were deeply studied, respectively, allelopathic potential, effective parts screening, allelochemicals extraction and identification, allelochemicals mechanism research,and so on were detected. The measuring indicators above all were conducted to explain the invasion mechanism in the physiological and chemical perspective, and tried to extract the herbicidal activity compounds.The main results were showed as follows:1. Biological characteristics of Conyza canadensisdetermination results of Conyza canadensis biological indicators during growth period showed that its growth period was from April to October,generally, Its growth rate was slower growth in April, gradually rapid in may,and vigorous during June and July; analysed the correlation between the biological traits of Conyza canadensis and effective accumulated temperature, it is concluded that the growth speed of thd ground part in Conyza canadensis was highly correlated to effective accumulated temperature, the growth rate with the increase of the effective accumulated temperature is highly relevant,too. All about Showed that reproductive strategy of Conyza canadensis was to achieve the largest accumulation of biomass in the short term.2. Physiology characteristics of Conyza canadensisTreated under drought stress by PEG-6000, the physiological response of Conyza canadensis under water stress has been analyzed. The results showd that under drought stress the numericals of free water, bound water and the ratio of free water/bound water presented a certain change, but no significant difference with control group, which meaned that Conyza canadensis have strong ability of hold water; under different water Stress, the small fleabane chlorophyll content of Conyza canadensis declined, but the ratio of chlorophyll a/chlorophyll b increases; At the same time, under drought stress, defense system of Conyza canadensis started:MDA content persistently increased, free proline content continued to rise. Antioxidant enzyme system appeared to rise and fall of trends. This small fleabane tests showed that the The experimental results proved,although biological membrane and enzyme system of Conyza canadensis are damaged by drought, its strong adaptability to improve material utilization in the body,which also showed that Conyza canadensis had multiple channels to adapt to drought stress. Through above change,a conclusion should be made that invasive plants have complex regulatory mechanism.3. Physiological ecology characteristics of Conyza canadensisBy measuring Photosynthetic diurnal variation of Conyza canadensis, it is concluded that the daily variation of net photosynthetic rate bimodal curve, has obvious "noon break" phenomenon, mean while the daily variation of transpRJation rate Basically appeared bimodal curve of. The variations trend of water use efficiency was also same as net photosynthetic rate. The correlation analysis between net photosynthetic rate and ecological factors displayed that net photosynthetic rate significant positively related to the effective radiation and temperature,while significant negative related to relative humidity. Under the condition of simulated sunlight and CO2, respectively measured the saturation point and compensation point for light and CO2 of Conyza canadensis.Found that the light saturation point (LSP) and light compensation point(LCP) of Conyza canadensis were 1634μmol·m-2·s-1 and 23.84μmol·m-2·s-1, respectively, which lay between the two associated plants, the difference being significant (p< 0.05). The Pmax(28.12μmol·m-2·s-1) of Conyza canadensis at LSP was much higher than those of the two associated plants. The apparent quantum yield (AQY) of Conyza Canadensis was 0.06, the difference was significant with Ixeris chinensis AQY, and however, there was no significant difference with Commelina communis AQY. The CO2 saturation point (CSP) and CO2 compensation point (CCP) of Conyza canadensis were 834.00 μmol·mol-1 and 23.69 μmol·mol-1, respectively; The Pmax of Conyza canadensis at CSP was 31.97 μmol·m-2·s-1 which lay between the other two species. The Carboxylation efficiency (0.078) of Conyza canadensis was the highest among the three species; The changes of photosynthetically active radiation and CO2 concentration had no significant influence on stomatal conductance or transpRIation rates of the three plants, however, the water use efficiency (WUE) was significantly effected. Those results showed that Conyza canadensis possess a higher photosynthetic rate and material accumulating ability. And higher productivity is one of important factors leading to successful invasion.4. Physiological and biochemical characteristics of Conyza canadensisThrough allelopathic potential analysis to Conyza canadensis found that its water extract had different degree of allelopathy to 9 kinds of receptor plants. Among them, the allelopathy of water extracts in aerial part was not obvious to some large seeds such as Abutilon, barnyard grass and so on, and even the allelopathy showed a boost, howeyer,For small seeds such as goosefoot, endive, Trifolium repens,the allelopathy showedinhibition, even the inhibition increased with increment of water extracts concentration, but the water extracts has no obvious inhibit or promote role to the grass kind of Kentucky bluegrass, tall fescue and perennial ryegrass. On this basis, further carried on the effective parts selection, the test found that the acetone extract of the stems dry powder vaConyza canadensis contained some allelochemicals which inhibited seed germination and seedling growth, through chromatographic column separating, active tracking, the preparative liquid chromatography purificating, high resolution mass spectrometry and nuclear magnetic resonance (NMR) identificating,the active material molecular was obtained. Its Molecular Weight was 428.3727.Its molecular structural formula was 3 beta-bean steroid-5-ene-7-ketone (3 beta hydroxysitost-5-en-7-one). Further analysis of 3β-hydroxysitost-5-en-7-one, the mechanism was to influent the soluble protein, SOD, POD and CAT of receptor plant, meanwhile the influence degree was closely related to its dosage,which instructed 3β-hydroxysitost-5-en-7-one break the balance of antioxidant enzyme system in receptor plant.