Invasive Characteristics Of The Forestry Harmful Plant Mikania Micrantha

Mikania micrantha H.B.K. is a world-wide invasive plant and it is also one of the worst harmful weeds for afforestration in China. Research on its invasibility is the theoretical base for forecasting its invasive direction, preventing and controlling its widespread, which made a systematic study on this weed become the urgent matter at moment. According to these, M. micrantha was researched by methods of laboratory control experiment and field survey in this paper. This paper aims to discuss the invasion-related characteristics of M. micrantha, mainly focusing on its spread, colonization, growth, reproduction and life cycle form. The main conclutions as follows:1) Colonization and route of spread. Anatomy of stem was initially used to discriminate the population age of M. micrantha, and the result indicats the close relationship between its spread at the ShenZhen gulf and development of local building projects. Further study on the microenvironment showed that there were no M. micrantha when soil pH and soil compaction were respectively 4.6 and <35 kPa at the beginning in the filled bay, while M. micrantha began to distribute when both parameters were respectively 5.6 and > 70kPa in 5cn- depth, i.e. After the soil environment improved, M. micrantha H.B.K. quickly colinized the habitat and became a dominant community, then harmed other plants.2) Photosynthesis and growth characteristics. Non-photosynthetic organs of M. micrantha had a powerful photosynthetic capacity. In the per SPAD( a greenness parameter measured by the commercial-available SPAD meter), electron transport rate of stems were 2.3 times than that of leaves and actual photochemical efficiency of PSII of stems were 3 times than actual photochemical efficiency of PSII of leaves. Electron transport rate of stems reached 4.5 μmol photonsm^-2·s^-1·SPAD^-1. At the same time, net photosynthetic rates was also observed in flower bud (37μmolkgDW·s^-1). Leaves of M. micrantha photosynthesized in a C3 pathway, while stems, petioles, nervations et al. may had a C₄ photosynthetic characteristics. This C3-C4 characteristic might contribute to the stronger adaptability to the varied habitats. Moreover, cambium of stems had lower pH than others, which could induce quick growth and karyokinesis of cell. Those photosynthetic and growthful characteristics were of significance for its invasion.3) Reproductive and spreading characterstics. Ratio of pollen quantity and ovule quantity of M. micrantha were 3410:1, but Rudbeckia serotina (syn.R.hirta) were 8160:1. The result indicates that pollen and the pillar heads of M. micrantha could be good for inset and germination, which reduced the loss of the pollen and decreased the cost of reproduction. Seeds of M. micrantha were light, and took the pappus, had various disseminated ways. Thelow cost for reproduction and various spreading ways of seed had important significance for its fast invasion.4) Dynamic life history form and intelligent adaptive characteristics. Study on the life history form of M. micrantha showed that vegetative growth of this weed, instead of sexsual growth and clone growth, was main growth type regardless of S type, V type, C type, and the transition types. This induced the high growth speed of M. micrantha, finally climbing and overlaying the native plant.Stem tine of M. micrantha could identify light signals and root tine could identify water signal. M. micrantha could judge those signals and adjust oneself to the environment, showing the intelligence of this weed. These intelligent behaviors of M. micrantha ensured its dominance in community.