The Invasive Characteristics Of The Forestry Harmful Plant Iva Xanthifolia Nutt.

Iva. Xanthifolia Nutt. is a kind of annual plant in Iva L.of Compositae, whose English name is Giant sumpweed. It could grow inside and outside farm fields, and in the roadside, village, and wastelands. The weed distributes in the northeast of China, North America and Europe. Iva. Xanthifolia, which is a kind of potential harmful weed, could usually be mixed in the crops, and do harm to forestry engineering measures including afforestation and seedlings growth, and so on. According to this, we systematically studied on the invasive characteristics of Iva xanthifolia. The main conclusion we got as following:1. The physiological and biochemical basis of Iva xanthifolia' s invasion. The contents of all kinds of metabolites in Iva xanthifolia are different, because of different growth stages, such as seeds, sprouts, seedlings, adults, and inflorescence. During our studying, we found that almost each metabolite got the highest content in the stage of seed or sprout. That might be related with breaking domancy for continuous growth in the stage of seed, and exuberant life activities in the stage of sprout. And the soluble sugars, such as fructose, glocuse, and sucrose were found accumulating in the stages of sprout and inflorescence for the most. That could be benefit to the fast growth and development. There were also certain contents of GA in the stages of sprout, seedling, and inflorescence and other stages in the growth oflva xanthifolia. As we all know that the certain contents of GA could promote the cell elongation, accelerate the growth of the plant, in order to foster the plant finishing its transformation from vegetative growth to reproductive growth. In addition, we found the highest contents of flavonoid and tannin in the stage of seed in Ira xanthifolia. Flavonoid and tannin, as substances of promoting propagation and anti-stress, could promote breeding a lot of future generations and resisting to environmental stress. Comparision with other seven plants in the same family, such as Cosmos bipinnatus Cav., Ambrosia artemisiifolia L., Ambrosia trifida L., Rudbeckia laciniata L., Mikania micrantha H.B.K.., Eupatorium adenophonm Spren., and Eupatorium odoratum (L.), we found that the contents of GA, flavonoids, tannins, and soluble sugars in different plants got regional differences. But different metabolites in each plant got no different interspecific regularity differences.In addition, in the environment of Iva xanthifolia, there usually got strong reflecting ability based on rubbish substances. It might accommodate photosynthesis through changing the leaves' sturctures, covering the thickness of pattern tissues and sporogenous tissues, the ratio of pattern tissues to sporogenous tissues, etc. Furthermore, the leaves of lva xanthifolia got strong photosynthesis, for instance, the highest net photosynthetic rate was 43μmol·m^-2·s^-1. Non-photosynthetic organs, such as stem, petiole, and genital mutilation, also obtain relative strong photosynthesis. And ETR could reach to more than 50 percent of photosynthesis. All these were the basis of lva xanthifolis's fast invasive characteristics, covering rapid colonizing, speeded growing and strong generating, and fast spreading.2. The rapid colonizing characteristics of Iva xanthifolia. Compare with other species in the same population, Iva xanthifolia had very strong occupy ability in its invasive environment, for its refined box dimension had reached to more than 1.9. Moreover, Iva xanthifolia could easy adapt to different soil compactness, soil pH value, and other environmental factors. In different environment, the development of root system involving primary root ,root hair zone and root canopy, and the development of other organ indexes covering its height, diameter and canopy turned to linear correlative relationship.Iva xanthifolia had strong photosynthesis, which could help itself effectively utilize light. And then transfer into the necessary energy, in the result that the plant could obtain more nutrient, and have stronger vitality.3. The speeded growing and strong generating characteristics of Iva xanthifolia. In room planting, we found that the fast germination happened from the third day to the fifth day with the rate of 13.2 seeds germination per day. Then turned to a little slower with the rate of 2 seeds germination per day. After the ninth day, there were almost no germination. The speeded growth of Iva xanthifolia happened from early spring to early summer.. From earl June to late July, height could reach to 1.98 cm.day^-1 in average., and 0.2 mm day^-1 for diameter. Then, the growth speed became slowly. Iva xanthifolia started into reproductive growth period. The grass could produce amount of pollen with structure of sag and swell which could benefit for pollen combining to pillar heads, increasing higher posibility of successful pollination and insemination. Iva xanthifolia could generate huge number of seeds, for example, each plant could produce 55289.8 seeds in average. All these provided guarantee for Iva xanthifolia's population diffuseness.4. The fast spreading characteristics of Ira xanthifolia. Short distance spreading of Iva xanthifolia is mainly by wind while far distance spreading is chiefly by vehicle. The number of Iva xanthifolia's seeds in unit area is linear decreasing from roadside to the middle of the road, with the reducing speed of 11.4 seeds per centimeter in average. The maximum reducing speed could reach to 20.8 seeds per centimeter. Diverse vehicle, covering shoes, bicycle tyres, gharry tyres and car tyres and other large transports, could carry almost all the seeds on the ground. All the characteristics foster Iva xanthifolia's the speeded spreading. Furthermore, the large-scale soil which was destroyed in one time, layed a foundation for the combination between the seeds and soil surface in a fast way.5. In a word, many intelligent behaviors emerged in the processes of physiological metabolism, reproduction, and spreeding, and the fast invasive characteristics covering rapid colonizing, speeded growing and strong generating, and fast spreading, ensured the predominance of Iva xanthifolia when it rivalized with other plants.