Study On Invasive Biology Of Alien Plant Conyza Canadensis

Conyza canadensis, an biennial or annual composite herb originating from North America, was widely disturbed in China, and now the species has became a common invasive plant. In order to reveal the ecological approach in relation to the spread of the exotic species and provide the important bases for effectively control and management, we studied its seed biology, allelopathy, root morphology, population and community ecology, and geographical distribution pattern. The main results were concluded as follows:1,In order to gain more information about the seed biology and distributing characteristics of C.canadensis and C.bonariensis, their seed production was evaluated, the influences of temperature, pH and NaCl stress on seed germination and early seedling growth were determined. The following results were obtained:①the achene numbers/individual for C.canadensis and C.bonariensis were about 400,000 and one million respectively. Their mean weight of 1000 seeds was about 0.02 g ~ 0.03g, and the average water content of seeds is about 32%~45%;②90% mature seeds of both species could germinate under favorable conditions.Most seeds of C.canadensis began to germinate after 2-d culture, which faster than C.bonariensis, and the seedlings emerge in succession after 2-8d culture.③C.canadensis grew well under moderate temperature(20℃~25℃), and could be adapted to soil environment with pH value ranging from 4~10, it prefers neuter soil condition;Compare with C.bonariensis, C.canadensis probably owned better resistance to water stress when the concentration of NaCl is not higher than 0.09 mol·L-1.These results showed that C.canadensis could exist in wider heterogenetic environments than C.bonariensis, which makes the former weed have wider distribution in China.2,We test the allelopathic influences of the aqueous extract from the leaves, stems and roots of C.canadensis on seed germination, root length and seedling height of four receiver crops including Brassica chinensis, Lycoperiscum esculetum, Cucumis sativus and Raphnus sativus.We also identified the allelochemicals of the extracts of C.canadensis by soxhlet extraction using GC-MS.The experimental results were as follows:①the allelophatic potentials of the extracts on the crop species varied with the different parts of C.canadensis.The aqueous extracts from C.canadensis leaves have strongest allelophatic effects on the four crop species;②the aqueous extracts from leaves, or stems, or roots of C.canadensis all have distinctly inhibitions on root growth, seedling growth and seed germination of crops, such inhibitions rose with the increase of the concentration of the aqueous extracts;③on the seedling growth of some crops, the aqueous extracts from C.canadensis leaves have double effects, positive at lower concentrations and negative at higher concentrations;④a total of 44 compounds including acid, alhocol, aldehyde, keton, ester, terpene, etc were identified by GC-MS, among them, acid, keton, tepene are the main components.3,The morphological characteristics of root system of Conyza canadensis were analyzed with EPSON V7000 root system analyzer and its supporting software (WinRHIZO). The results showed that:①the root system of Conyza canadensis grew rapidly from May to July, and reached its peak in flowering period, then achieved stability in September or October.②along with the increasing of plant height, underground morphological parameters of Conyza canadensis have increased with different level.③morphological parameters of aboveground included leaf length, leaf width, leaf number, dry weight of aboveground and underground. Morphological parameters of underground included root length, project area,surface area, average diameter,root volume,tips,forks,crossings,and noflinks.These parameters have obvious relationships with population density. The influences of population density on the parameters of root morphology at different diameter classes were different, roots with diameter size range from 0.0 mm to1.0 mm were more restricted by the population density.4,The ecological importance values of herbaceous plants were surveyed at 498 sites of different habitats in the area of Yangtze River Delta and its adjacent areas, a total of 421 species were recorded from these sites. The niche breadth and the niche overlaps of these plants were calculated. Based on the above data, the relationship between plant distribution and environmental factors were analyzed using Canonical Correspondence Analysis (CCA). The results showed that:①Solidago canadensis, Galium aparina, Vicia sativa, Humulus scandens, Conyza bonarinisis, Geranium carolinianum, Ranunculus muricatus, Euphorbia beliocopia have bigger ecological importance values than C. canadensis, the latter ranked as 9th among the 421 species in the surveyed sites.②the top 10 weeds with the widest niche breadth were Galium aparina, Conyza bonarinisis, Vicia sativa,Geranium carolinianum, Ranunculus muricatus, Conyza canadensis, Solidago canadensis, Humulus scandens, Veronica persica, Euphorbia beliocopia. These weeds with strong ability to adapt to the environments were major invasive plants of Yangtze River Delta.③Half of the first twenty exotic weeds having bigger niche overlaps with C. canadensis belong to the family Compositae. It suggested that C.canadensis required the similar environmental conditions for survival with these weeds.④the analysis of correlation between ecological importance values and intensity of human activity indicated that Setaria glauca, Eleusine indica, Digitaria sanguinalis, Solidago canadensis, Astersubulatus, Xanthum mongolicum, Conyza canadensis, Echinochloa colonum, Lactuca indica, and Euphorbia maculate were most suitable for the interference environment.5,A total of 282 invasive alien plants were recorded from 74 geographical units in China, and 11 environmental variables including climatic and social factors were also recorded. Based on the above data, the geographical distribution pattern of 282 invasive alien plants in the 74 geographical units and influencing factors were analyzed using Detrended Correspondence Analyses (DCA) and Canonical Correspondence Analysis (CCA). The main results are as follows:①In the 74 geographical units, Conyza canadensis, Amaranthus spinosus, Erigeron annuus, Alternathera philoxeroides, Chenopodium ambrosioides, Pharbitis purpurea, Datura stramonium, Amaranthus viridis, Pharbitis nil, Amaranthus retroflexus, Bidens pilosa and Eichhornia crassipes are widely distribution in mainland of China.②The geographical distribution of invasive plants in China were divided into three regions:the tropical-south subtropical region, central(north)sub-tropical region, and the temperate region.In the first region, the main invasive plants are Lantana camara, Mimosa pudica, Ageratum conyzoides, Amaranthus spinosus, Conyza canadensis, Euphorbia hirta, Ipomoea cairica, Alternathera philoxeroides, Bidens pilosa and Synedrella nodiflora; in the second region, the main invasive plants are Erigeron annuus, Conyza canadensis, Amaranthus spinosus, Chenopodium ambrosioides, Lepidium virginicum, Phytolacca americana, Eleusine indica, Mirabilis jalapa, Alternathera philoxeroides and Bidens pilosa; while in the third region, Amaranthus retroflexus, Conyza canadensis, Pharbitis purpurea, Erigeron annuus, Hibiscus trionum, Chenopodium hybridum,Sonchus oleraceus,Avena fatua, Datura stramonium and Amaranthus viridis are the ten main invasive plants.③The main meteorological factors influencing the distribution of invasive plants in China, if ranked as from high to low, are annual average precipitation, annual average temperature, annual extreme minimum temperature, frost-free days and annual accumulated temperature, while annual extreme maximum temperature and annual sunshine hours were of little influence. Human population density and transport density also play important roles on the distribution pattern.④Conyza canadensis has the similar pattern of geographical distribution and ecological distribution with Amaranthus viridis, Erigeron annuus, Pharbitis purpurea, Veronica polita, Datura stramonium, Datura metal, Daucus carota, Phytolacca Americana, Eichhornia crassipes, Veronica persica.Together the above experimental results, its strong sexual reproduction capacity, broad range of habitats, significantly potential of allelopathy, and strong plasticity of root system, all which provided an important biological basis for successful invasion of Conyza canadensis. Through the comparison of ecological importance value, niche breadth, niche overlap, ability to adapt to the interference environment, as well as pattern of large-scale spatial distribution, reveal that Conyza canadensis is one of the most important species of invasive plants in our country. Therefore, relevant departments should pay attention to the integrated management of this invasive plant.