Studies On Invasive Biology And Integrated Management Of The Exotic Plant Crassocephalum Crepidioides

Crassocephalum crepidioides is a new exotic plant in China.In order to effectively control and utilize the exotic species,predict its potential distribution range and habitats in China,we studied its reproductive biology,stress physiology,population niche,Allelopathy,and also determined the content of the heavy metal elements in the plants and its nutrient values.The main results are as follows:1.The seed s of C.crepidioides almost have no dormancy period,and are able to germinate immediately after their mature,with a germination rate as high as 100%.Their seeds,even saved for one year in dry,still kept alive.Compared with the seeds of other weeds with dormancy,those of C.crepidioides could germinate even and quickly in favorable environments,which will lead to death of a great number of seedlings if they meet unfavorable conditions later,and thus limit their populations expansion;2.Light is necessary for the seeds of C.crepidioides to germinate,which indicate that appropriate soil tillage,mainly by ploughing will reduce the germination of C.crepidioides and thus control this exotic invasive plant;3.The seeds of C.crepidioides are sensitive to NaCl,their germination was inhibited when treated with NaCl at a concentration of 0.05 mol·L^-1.Almost no seeds of C.crepidioides were able to germinate when treated with NaCl at a concetration of 0.15 mol·L^-1;4.Relative wider adaptation range for the seeds of C.crepidioides to environmental pH conditions was observed during our experiments.Their seeds could germinate with a percentage of 82.67%when treated in the solution with pH from 4.00～10.00;5.Treated under 15℃～30℃,the seeds of C.crepidioides had higher germination rate(≥98.00%),even treated under 35℃or 10℃,some seeds still germinated.Compared with that at lower temperature,the inhibitory effect on their seed germination at higher temperature is stronger;6.The seeds of C.crepidioides are able to germinate in drier conditions, with a germination rate as high as 66.67%in soils with 5%humidity;7.Wind spreading experiment showed that the seeds of C.crepidioides and other five Compositae species could be spread to a range of 4 m or more far from the mother plants;8.Crassocephalum crepidioides has higher net photosynthesic rate(19.98μmol CO₂·m^-2·s^-1),light compensate point(20.16μmol·m^-2·s^-1),light saturation point(1311.88μmol·m^-2·s^-1),showing its adaptation to sunny environments.9.Experiments showed that MAD content in the leaves of C.crepidioides treanted with 0.07 or 0.14 mol·L^-1NaCl concentration was not significantly different from that of control,indicating that C.crepidioides is able to grow the environment with NaCl at lower concentraion.When slightly stressed by NaCl, The growth of C.crepidioides in height was inhibited by NaCl at lower concentration,but could be compensated by the increase of leaf number and producing more branches.Such response of its stems and leaves to lower NaCl stress facilitates the species to grow in the environments with NaCl at lower concentration.10.Treated under 5℃or 42℃for 48h,the content of MDA,soluble sugar and soluble protein,as well as the activity of POD in the leaves of C. crepidioides are not significantly different from those of the control,indicating that C.crepidioides is not very sensitive to high temperature(42℃)or low temperature(5℃).Therefore,this exotic plant might have wider potential geographic distribution range in China.11.Treat with either paraquat or glyphosate,the content of MDA and Proline,as well as the POD activity increased,while the content of soluble protein and the SOD activity decreased,which indicated that both paraquat and glyphosate caused obvious damages to their cell membrane,inhibit the formation of relative protein,thus inhibit its growth.The application of paraquat or glyphosate with a concentration of 1/2 dose recommended could control the species effectively;12.In the areas(North Mountain,Jinhua,Zhejiang province)invaded by C. crepidioides,C.crepidioides has a niche wide of 0.4305,ranked as 7^thamong the species in the surveyed sites.The accompanied weeds,according to their niche overlaps with C.crepidioides from high to low,are Acalypha australis, Digitaria sanguinali,Erigeron annuus,Setaria viridis,Rostellularia procumbens,Galinsoga parriflora,Solanum nigrum,Chenopodium album, Eclipta prostrata,Amaranthus tricolor,Echinochloa crusgalli,Artemisia lavandulaefolia,and Lagedium sibiricu,ect.Niche analyses showed that both of frequency and niche width of C.crepidioides are lower than those of Erigeron annuus,Setaria viridis,Digitaria sanguinali,which shows that the weediness of C.crepidioides is not very strong.13.The aqueous extracts from the leaves and stems of C.crepidioides contain some kinds of allelochemicals,which could inhibit the seed germination and seedling growth of other species,but had no inhibitory effects on or even facilitate its own growth in young stage,which might protect its own young generation from competing with other accompany species,thus facilitate to expand it population.14.Determination on the content of heavy metal elements in C. crepidioides and other 23 wild vegetables showed that the risk of damage to our health as a vegetable ranked 16 among the 24 wild vegetables.Attention should be paid to the harmful effects on our health when we utilize this plant as a vegetatbel.Together the above experimental results,we found,C.crepidioides is able to grow under wider range of temperatures and pH values in soils. Crassocephalum crepidioides has narrower range of illumination than comnyza Canadensis,Erigeron annuus,and the niche width of C.crepidioides is than those of Erigeron annuus,Setaria viridis,Digitaria sanguinali,Therefore,the invasiveness of C.crepidioides is not stronger than thoses of other common weeds and worst invasive exotic plants.For control purpose,appropriate soil tillage,mainly by ploughing will reduce the seed germination and the seedling emergence of C.crepidioides,and the treatment with paraquat will control the species quickly and effectively.Because of the accumulated effect of some toxic heavy metal elements,attention should be paid to the risk of C.crepidioides for our health if the plant is utilized as a wild vegetable.