Wan Fanghao

Comparison of impacts of invasive weed, Ambrosia artemisiifolia, and native weed, Digitaria chinensis, on soil enzyme activity and fertility.

The soil enzyme activity and soil fertility in the invasive ragweed (Ambrosia artemisiifolia) and native weed (Digitaria chinensis) growing-plots were analyzed and compared by the same experimental garden methods. The results show that compared to non-vegetation and native-weed, the invasive ragweed significantly increases soil nutrient availability, especially, available K content in the invasive ragweed plots is 3.6 and 1.3 times of those in the non-vegetation and native weed plots, respectively. Compared to non-vegetation and native weed plots, the invasive ragweed plot has significantly higher activity of soil enzymes. In a conclusion, the invasive ragweed (A. artemisiifolia), has a more strong capacity to improve soil available fertility and activity of soil enzyme than the native weed (D. chinensis), which benefits its competition with native species.

Effects of exotic plant Ageratina adenophora invasion on mycorrhizal fungal community

The invasion of exotic plants and probability of successful invasion are affected by the interaction between exotic plants and soil microbes in invaded habitats.Furthermore,interactions among mycorrhizal fungi(MF) and exotic plants have been the focus of the response of soil microbial mechanisms to plant invasion.This study used nested PCR to detect MF in roots and rhizosphere soils of native weeds and A.adenophora in native weeds dominated community,A.adenophora and native weeds mixed community,and A.adenophora dominated community in A.adenophora invaded habitats.The results showed that MF community structures were different for different invasion phases.Glomus intraradices clones were detected in roots of native weeds grown in native weeds dominated community.G.intraradices clones were also noted in roots of A.adenophora grown in A.adenophora and native weeds mixed community.Only one Glomus(Glomus sp 2) clone was found in the roots of native weeds grown in A.adenophora and native weeds mixed community.No MF was detected in the roots of A.adenophora grown in A.adenophora dominated communities.Also two Glomus(Glomus sp 1 and Glomus sp 2) clones were obtained in the rhizosphere soils of A.adenophora dominated commu-nity.Trichoglossum hirsutum,Tricholoma saponaceum,Xylobolus subpileatus and Sarcodon imbricatus were detected in rhizosphere soils of A.adenophora grown in A.adenophora and native weeds mixed community.Camarophyllopsis hymenocephala,Lepista irina,T.saponaceum and Panellus serotinus were found in rhizosphere soils of native weeds grown in A.adenophora and native weeds mixed community.T.saponaceum was found in rhizosphere soils of native weeds grown in native weeds dominated communi-ties.MF communities were changed by A.adenophora invasion and ectomycorrhizal fungi(EMF) more likely habited native weeds rhizosphere soils than A.adenophora rhizosphere soils.Arbuscular mycorrhizal fungi(AMF) accumulated more in rhizosphere soils of exotic A.adenophora than in native weeds rhizosphere soils.The probability of invasion changed MF community response to A.adenophora invasion,which suggested that A.adenophora heartened AMF in rhizosphere soils and induced positive AMF feedback,which enhanced A.adenophora invasiveness.The study highlighted one of the important soil microbial mechanisms of A.adeno-phora invasion in southeast China.

Response of the alligator weed flea beetle,Agasicles hygrophila( Coleoptera:Chrysomelidae) to overwintering protection and its controlling effect on alligator weed Alternanthera philoxeroides( Amaranthacese: Alternanthera)

The alligator weed flea beetle,Agasicles hygrophila( Coleoptera: Chrysomelidae) is a biological control agent of the alligator weed Alternanthera philoxeroides( Amaranthacese: Alternanthera),a worldwide invading weed. Low temperature and frost stress in winter-spring seasons are the key factors that affect A. hygrophila. To explore whether the protections used in habitat could increase the population of overwintered A. hygrophila,we investigated and compared the populationnumber,structure,distributing characteristic in spatial niches of A. hygrophila and the controlling efficiency of A.hygrophila on A. philoxeroides in protected habitat( PH) with those in natural habitat( NH). The investigation was phased with the variation of air temperature and the elapse of time. Low temperature stage was from 21th,January to 9th,April,2009,followed by temperature rise period from 15th,April to 1st,May,and the third investigated period which was the first emergence time of beetle adults in NH from 1stto 29th,June. The protected habitat was constructed by covering plastic film on net room before low temperature and freezing came. The results showed that A. hygrophila could overwinter smoothly and no dormancy was observed in protected habitat at low temperature in winter-spring time. Adults gadded and fed on up-right stems of A. philoxeroides both in sunny and air temperature rising day in winter-spring time,but were inactive and stayed creep layer of weed or surface or crevice of soil at overcast,rainy or low temperature time. Beetle adults in protected habitat laid eggs in early April. There was a rapid increasing of the populationwhich played an important role in controlling the above ground parts of A. philoxeroides. Only a few beetle adults can be found in natural habitat even at the beginning of June. Consequently,the weed grew very well due to the low density of the beetle population which was difficult to play the role of a biocontrol factor. Comparing the results obtained in the first day with that in 15th,June,the increasing rate of stem height of A. philoxeroides in this interval of time were-13.91% in the protected habitat and-2.94% in the natural habitat,respectively. The stem height of A. philoxeroides in the natural habitat was significantly higher than that in the protected habitat. The control rate of a plant biomass of A. philoxeroides by A. hygrophila in the protected habitat was 47.56% which was significantly stronger comparing with the control rate of 4.89% in the natural habitat. The control effect to leaves of A.philoxeroides in the protected habitat was extremely better as compared with that in the natural habitat in the interval of time from 15thto 29th,June. There were no leaves left on stems of A. philoxeroides plants as leaves being either eaten up by A.hygrophila or withered after attacked by A. hygrophila in the protected habitat. The rate of damage stem,rate of stem bore hole and the number of stem bore hole per plant in the protected habitat were significantly higher than that in the natural habitat. These results suggested that the overwintered A. hygrophila population could be significantly increased by covering plastic film to protect the habitat. The beetle adults in protected habitat could lay eggs ahead of time compared to that in the natural one,thus could effectively control the growing of weed.