Comparative Study Of Reproductive Characteristics Of An Invasive Plant,Salidago Canadensis Under Common Gardens

Solidago canadensis L.belonging to Composite,is a perennial invasive alien plant and native to Northeast of America.Now it becomes one of the world most harmful weeds.Solidago canadensis L.was introduce to Shanghai and Nanjing as ornamental plants during 1930s.Then it escaped,spread and became a malignant invasive weed which is harmful to agriculture and biodiversity in southeast of China after 1980s.The invasiveness of Solidago canadensis L.is mainly attributed to strong reproducibility,in particular,sexual reproduction ability.Reproductive characteristics of different cytotypes from native and invasive range were compared under common gardon in this paper.Crosses among different cytotypes were conducted,and pollen germination and pollen tube growth behavior were observed by fluorescence microscope and the viability of seeds was tested to assess the compatibility of the cross combinations and elucidate the mechanisms of polyploidization through influencing reproductive characteristics,leading to successful invasion.The main results are given as followings.Studies of reproductive characteristics between different cytotypes In the common garden experiments,the results of testing showed that pollen viability of polyploids ranged from 62.9%-67.9%,was significantly higher than that of diploid with 55.2%(IN2x)and 56.2%(NA2x)respectively.The stigma receptivity of polyploids ranged from 78.0%-84.4%was significantly higher than that of diploid IN2x and NA2x in 78.0%and 69.2%respectively.The results indicate that increased ploidy level beneficially improved sexual reproductive ability.There is no difference in the pollen viability and stigma receptivity between native and invasive range,which indicates that the higher sexual reproductive ability of polyploids may be the consequence of pre-adaptation.The phenophase of early blooming stage of polyploids were 220.3th-284.7th day(Julian Day).The Julia Day of IN2x and NA2x were 173.7th and 161.6th respectively.The flowering phenophase of hexaploids and tetraploids was significantly delayed compared to diploids.Furthermore,the flowering time of tetraplids was earlier than hexaploids.The time of flowering significantly had positive correlation to the ploidy level.The later flowering prolonged vegetative growth duration so that the plants could accumulate more biomass and energy for subsequent sexual reproduction.The flowering time of the same ploidy populations from invasive ranges was significantly earlier than that from invasive ranges and flowering time of both native and invasive populations overlapped.The flowering phenophase pattern indicates that the flowering time variation may be resulted from pre-adaptation and rapid post-introduced adaptation evolution.Studies of cross compatibility between different cytotypes of Solidago canadensis L.A test of pollination compatibility with pollens from same tubular flower,from same plant but different flowers,from same plant but different clones showed self-incompatibility of Solidagocanadensis.Crosses between same cytotypes but xenogamy demonstrated that pollens normally germinated on stigmas,and pollen tubes grow into overy normally,which indicates the good cross compatibility.Crosses between homoploidy ployploid produced viable seeds with germinatin rate of 1.1%-34.4%while diploid did not any seeds.This indicates that polyploidization improved sexual reproducibility of S.canadensis.Moreover,seed viability of invasive populations significantly were significantly higher than native populations,which shows that the fecundity may be the consequence of pre-adaptation and the better sexual reproduction ability of invasive populations may be the consequence of a rapid post-introduced adaptation evolution.Cross between different geocytotypes showed that cross-compatibility of cross combinations between homoploidy cytotypes from different ranges was much higher than cross-compatibility between heteroploidy cytotypes.Cross-compatibility of tetraploid X hexaploid was much better than the other cross combinations between different ploidy level.Only IN6x×NA6x(4.4%)and IN6x×IN4x(7.8%)cross combination could produce viable seeds but the later seeds did not grow into plants.The results of mentor experiments showed that crosse barrier between different ploidy levels could not be overcome when mentor pollen existed.Good cross-compatibility of cross combinations between homoploidy cytotypes but from different ranges could accelerate the process of post-introduced adaptation evolution.Cross experiments may indicated the closer relationship between tetraploid and hexaploid.Reproductive biology of Solidago canadensis L.from native ranges in Nanjing common garden experiment Although S.canadensis populations expansed through sexual reproduction，the sexual reproduction characteristics of native populations remains unclear under common gardens in introduced range.Under common gardens in Nanjing,31 native populations collected from north America were compared on their seed vitality,seed yield,and analysied on the relationship between flowring time and latitude of the collection site.The results showed that they were negatively correlated to latitude.Populations above 35.5 parallel of north latitude produced higher viability seeds,and higher seed yield.Flowering time of some native populations overlapped with invasive populations.Seeds produced by populations from northern native ranges had no viability or low viability with germination rate 0-20%.Their flowering time occurred as early as in June.The sterility of those populations were attributed to embryo abortion.The number of embryo abortion was negatively correlated to temperature during embryo developing.All above indicate that sexual reproduction characteristics of S.canadensis may be the effects of pre-adaptation.In summary,invasiveness of S.canadensis is the comprehensive effect of pre-adaptation and post-introduced adaptation evolution.