| Alternanthera philoxeroides (Mart.) Griseb. is an exotic aquatic-terrestrial plant that was introduced into China from South America. This species distributes widely and often extends hollow stems over the surface of the water, forming interwoven, floating mats. The capacity of growing and spreading rapidly of this species have caused many disadvantage to ecosystem and development of society and economy. However, the mechanisms of its invasion are not clear. This paper studied asexual reproduction, ecological adaptation and the effects on native aquatic plants of A. philoxeroides in order to analyze its invasion mechanisms.The system of root and underground stems of terrestrial A. philoxeroides is huge, and the reproduction capacity of which is high. Thick root numbers of A. philoxeroides were decreased with increasing soil depth. The maximal number and diameter of thick root were found in 0-10cm and 10-20cm depths respectively. Most of thick root biomass was found in 0-30cm depths. The maximal number of adventitious bud (1260 buds) was found in 0-10cm depths. Underground stems mainly distributed in 0-20cm depths. However, The axillary buds generated from underground stem were mainly distributed in 0-10cm depths. The positive relation between the capacity of generating bud and the thick root diameter as well as the thick root biomass was found. A large number of adventitious bud generated when thick root sinked into water. Most of adventitious buds branched before they emerged soil.After the floating-mat of A. philoxeroides stayed on the land and experienced the winter, the prostrate stems could be separate into 3 types according to water content: air-dry stems, wither stems and fresh stems. All the stems were sinked into water for 4 weeks in order to study the reproduction capacity of stems. The results showed that: Air-dry stems had no capacity of reproduction, but fresh stems had the maximal capacity. The mechanisms of generating bud earlier than that of root would help A. philoxeroides disperse in the water.Light and grazing are the two important factors that influence the invasion of exotic plants. The work of the effect of shading and mowing on A. philoxeroides showed that: shading had no effect on leaf number and leaf biomass of unmown plants, but on mown plants. SLA, LAR and leaf biomass was increased by shading treatments.Shading led to lower stem biomass. thick root biomass, R/S. RGR and TRMR. but had no effects on SMR and FRMR. Mowing had no effects on thick root thickness, maximal root length, fine root biomass, SLA. LAR, R/S and biomass allocation, but on stem biomass of plants that both grew in shading and full sunlight habitats. In addition, mowing led to lower RGR, internodes number, shoot length and leaf biomass of plants grew in shading habitats.Photosynthetic capacity, water use efficiency (WUE) and light use efficiency (LUE) of many invasive exotic plants were greater than native plants. Photosynthetic parameters of aquatic A. philoxeroides, terrestrial A. philoxeroides, L. hexandra, Z. latifolia and P. communis during early growth stages, florescence (or middle growth stages) and flower-fruit stages were measured. The results showed that: Midday depressions of aquatic A. philoxeroides and terrestrial A. philoxeroides were not found in April, but found in June. Midday depressions of terrestrial A. philoxeroides also occurred in October, and which of L. hexandra, Z. latifolia and P. communis did not occur at any growth stage except in April. The mean value of photosynthetic rate, 7r and LUE of aquatic A. philoxeroides and terrestrial A. philoxeroides expressed on a day were greater than that of three native aquatic plants during every growth stage. The value of maximal photosynthetic rate of A. philoxeroides was similar to C4 plants, and which was greater than 3 native aquatic plants. The mean value of WUE of aquatic A. philoxeroides expressed on a day was the maximal in April, and which only lower than Z latifolia in June. The values of apparent quantum yield (AQY) and carboxylation efficiency (CE) of aquatic A. philoxeroides and terrestrial A. philoxeroides were higher than that of 3 native aquatic plants. On the other hand, there were no differences in dark respiration rates (Rd) and light compensation point (LCP) between A. philoxeroides and 3 native aquatic plants. Light saturation point (LSP) of aquatic A. philoxeroide and terrestrial A. philoxeroides was similar to that of Z latifolia and P. communis, but greater than that of L. hexandra. CO2 compensation point (CCP) of aquatic A. philoxeroides was the minimal. CO2 saturation point (CSP) of aquatic A. philoxeroides and terrestrial A. philoxeroides was similar to that of Z latifolia, but lower than that of L. hexandra and P. communis, respectively.There were 13 native species (including 3 life forms: free-floating, emergent and submersed) co-existed in the floating mats of A. philoxeroides in Changgang cannal, and which belonged to 12 genera, 10 families. There were 2 species belong to Hydrocharitaceae, Najadaceae and Gramineae respectively, and only 1 species belongto other families. The biomass of emergent plants was the maximal and that o\' submersed plants was minimal, respectively.There were significant effects on the leaf width, spacer length, root length, plant height and leaf number of//, dubia caused by the mats of A. philoxeroides. However, the mat of A. philoxeroides had no effect on the leaf length, biomass per plant and clones number of H. dubia. The branch level, branches number, plant biomass and plant height of P. malaianus were decreased significantly when grew under the mats of A. philoxeroides. Plant density, winter bud density, leaf number and plant biomass of V. spinulosa were decreased with increasing the biomass of A. philoxeroides. Furthermore, no significant variation in plant height of V. spinulosa that grew under and outside the mat was found. The biomass per winter bud was increased when plants grew under the mat.
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