Ecological Significance Of Polyploidy In The Invasion Of Solidago Canadensis In China

Many researches on the functional traits and genetic characteristics indicate that invasive plants are different from non-invasion plants. Barrett found that almost all of widespread weed were polyploid, and deduced that polyploid is likely to become the invasive species. Recent studies indicate that interspecific variation in ploidy level in species is associated with invasiveness, and polyploids are dominant invasive forms rather than diploids within species. Hence, the invasive potential depends on not only the variation in ploidy of a species but also the ploidy level of a cytotype. Although the reason is still unclear, it has been proposed that a broader tolerance of environmental conditions in polyploids, their greater potential of rapidly evolving with an ability to carry abundant genetic diversities and the potential for duplicating genes and producing new functions in the longer term might be the reasons to explain their success. Solidago canadensis L., a perennial herb (Asteraceae) native to North Ameriea, is a worldwide invasive spcies that has been expanding its distribution. In China, Solidago canadensis has been included in the second batch of alien invasive species list, and has caused tremendous ecological and economic losses in China..Solidago canadensis has long been known to include diploid (2x=18), tetraploid (2x=36), and hexaploid (2x=54) cytotypes in North American. Most previous studies have been focused on the biological characteristic or chemical methods to control Solidago canadensis. But few have been considered the role of ploidy. To understand the significance of polyploidy in Solidago canadensis invasions, studies on ploidy level in Solidago canadensis L. in North America and ecological features of polyploids in China should been paid close attention to. We focused on the process of residence and population establishment of Solidago Canadensis in this study. Ploidy levels were compared between North America and China. Several techniques were included:flow cytometry, molecular marker analysis and common garden experiment to explore the role of ploidy during the invasion of Solidago canadensis. The results are shown as follows:To understand the significance of polyploidy in biological invasions, we compared ploidy levels in North America and in China. DNA ploidy levels in a total of346plants collected at69localities were determined by flow cytometry. In the native range, diploid (2x=18), tetraploid (2x=36) and hexaploid (2x=54) plants were detected, two populations with mixed ploidy were also found in the native range. There was a low degree of geographical separation among the ploidy levels. DNA diploids largely prevailed within the native range. In China, only tetraploid and hexaploid plants were found, tetraploids were detected for the first time. Diploid plants were not discovered in the invasive range."Huangyinghua" is cultivated in China and belongs to the S. canadensis L. complex, All "Huangyinghua" individuals were found to be diploid (2x=18). China plants were predominantly hexaploid (77%), with23%of the samples found to be tetraploid, populations with mixed ploidy were common (14.7%). The DNA indices of invasive hexaploids were significantly lower than that of native hexaploids, the DNA indices of native and invasive tetraploids were found non-significant using the t test. Endopolyploidization phenomenon existing vegetative organs of invasive populations was detected for the first time. Our data suggested that polyploids had a stronger invasibility than diploids and polyploidyzation is inner power for successful invasibility in the species in China. It is suggested that polyploid cytotypes of S. canadensis L. likely have multiple origins from different diploid lineages.The genetic diversity among39hexaploid Solidago canadensis populations,8mixed ploidy Solidago canadensis populations and10tetraploid Solidago canadensis populations from introduced range in China and3hexaploid populations,3tetraploid populations,3diploid populations from native range in the United States was analyzed by using ISSR. The results showed that Nei’s gene diversity, Nei’s gene diversity and shannon’s information index in species from native range were higher than those tested from introduced range in China. There were obvious gene differences between different Solidago canadensis cytotypes. Hexaploid population had the genetic diversity among cytotypes. Solidago canadensis in originally introduced region in China had intimate genetic relationships and species from native range, indicating that Chinese populations may originate from sample region of native range. The AMOVA (Analysis of Molecular Variance) and Wright’s F-Satistics displayed that genetic differentiations exist not only among the introduced population and native population but also among different cytotype populations. Regional comparisons show low levels of genetic differentia’tion in introduced range in China. It will provide the evidences for bottleneck effects on invasive population, polyploidy incresae the genetic diversity and hexaploid populations had more evolutionary potential than tetraploid Solidago canadensis populations.Different geographic populations from China and nine different geographic North America were considered in this study. A series of experiments of ploidy appraisals are shown as follows:germination trait testing at high temperature, morphometric difference test and so on. The results indicated that length, width, weight and other indicators of seeds of diploid are significantly lower than those of polyploidy. Moreover, germination percentages and indices at normal and high temperature of seeds of diploid are significantly lower than those of polyploid. It was significantly different between the polyploid of native range and invasive range too. Length, width, weight and other indicators of seeds of hexaploid of invasive range are significantly higher than those of tetraploid of invasive range and hexaploid of native range, germination percentages and indices of hexaploid seeds of invasive range at normal and high temperature are significantly higher than those of tetraploid in invasive ranges and hexaploid in native ranges.Therefore, successful invasion of Solidago canadensis is mainly due to polyploidy.Successful invasion is facilitated by introduction of pre-adapted genotypes. In addition, it does lead to phenotypic changes related to fitness or competitive ability of introduced plants. Polyploidy appears to be over-represented in invasive plants, but differences between cytotypes in growth strategies including trade-offs among plant traits have received little attention so far in the context of biological invasions. Solidago canadensis were cultured in the greenhouse to test the differences in fitness (biomass) and competitive ability (vegetative size, specific leaf area, leaf dry matter content and root-shoot ratio) between diploid and polyploid cytotypes. Diploid, tetraploid and hexaploid genotypes occur in the native range, whereas only tetraploids are present in the introduced range. In the native and introduced range, diploid and polyploid genotypes had different growth strategies. Tetraploid and hexaploid genotypes had higher SLA, RSR, leaf area, shoot biomass, root lenth, root number, stem height than diploid ones.The maximum net photosynthetic rate, stomatal conductance and transpiration rate of polyploid genotypes were significantly higher than those of the diploid. There were no significant variations in parameters of chlorophyll fluorescence between diploids and polyploid genotypes.Thus, tetraploids and hexaploids appeared more competitive than diploids, which could explain, at least partially, the invasion success of the pre-adapted tetraploid and hexaploid genotypes. The comparisons of native and introduced hexaploids, tetraploid genotypes revealed differences in traits linked to competitive ability, which could be associated with novel selection in the new environment. Introduced tetraploid and hexaploid genotypes had higher SLA, RSR, leaf area, shoot biomass, root lenth, root number and stem height than native ones, but the maximum net photosynthetic rate, stomatal conductance, transpiration rate of introduced polyploid genotypes were significantly lower than those of native ones, In the introduced hexaploids, tetraploid genotypes, we found evidence for a competition-defence trade-off, which polyploid genotypes in introduced ranges may decrease photosynthesis production allocation for defenses and increase photosynthesis production allocation for vegetative growth, the increased allocation for vegetative growth, may increase resource capture ability and efficiency and facilitate successful invasion. Resource capture ability and photosynthesis efficiency and PSII resistance to hight tempertature of the hexaploids were significantly higher than those of the tetraploid, Thus hexaploids had more invasiveness.In order to explore the thermal adaptability of different cytotype of Solidago canadensis, relationship between ploidy level and latitude/mean temperature of the seventh month was studied, heat tolerances of different cytotype of Solidago canadensis planted in common garden were compared, free proline content, Cu/Zn-SOD activity, H2O2content under controlled high temperatur were measured. Results show that no obvious geographical pattern in the distribution of the three ploidy cytotypes was observed found, we found a pronounced shift in the relative frequency of diploid and tetraploid, hexaploid cytotypes. Only hexaploids were found in the China. Geographical distribution of cytotypes was effect by high temperature.Heat tolerances of different cytotype of S. canadensis had significant difference. Comparing with diploid, tetraploid and hexaploid have lower accumulation of H2O2, proline, but higher productions of antioxidant enzyme activities, which indicated they has suffered lower injury and better protecting mechanism,allowing them to tolerate certain extent of high temperature stress. We found evidences on S. canadansis in this study that polyploidization lead to increased heat tolerance of S. canadansis and increase the invasion success.Goldenrod is an invasive plant species in many countries except North America but a cut-flower species worldwide. There is a need to generate and propagate goldenrod clones efficiently for research and commercial purposes. A callus induction and plantlet regeneration system was developed by studying the influence of explant type and different concentrations of plant growth regulators. The highest callus production from leaf segments was obtained on Murashige and Skoog’s medium (MS medium) supplemented with1.0mg/L naphthalene acetic acid (NAA) and1.0mg/L6-benzylaminopurine (BA). Adventitious shoots could be regenerated directly from leaf explants without an intermediate callus phase with the highest shoot induction percentage of87.2%. The largest number of adventitious shoots per leaf explant (3.2) was obtained on MS medium supplemented with0.4mg/L NAA and2.0mg/L BA. MS medium supplemented with0.1mg/L NAA and1.0mg/L BA was the best medium for axillary shoot regeneration from nodal segments. The highest root number and longest roots occurred on half-strength MS without the addition of any growth regulator. Rooted plantlets were then transferred to a soil-based growth medium, placed in a greenhouse, and acclimatized with100%success. All surviving plants grew normally without showing any morphological variation when compared to those grow from seed. This regeneration protocol may be used to produce certain biotypes of goldenrod suitable for genetic transformation rapid propagation of goldenrod for commercial purposes or for screening fungi and toxins as potential biocontrol agents against this weed.In conclusion, the results suggest that polyploids improve the vitality and dispersal of offspring, maintain occupancy of colonized sites and increase resource capture ability. Polyploids maybe possess pre-adapted traits and the combination of traits which make them inherently more invasive than diploids. Hexaploid carries greater genetic diversity and the potential for evolving new functions in the longer term due to its duplicated genes. Hexaploid plants can quickly break through the limitations of genetic bottleneck and quickly reallocate resources for a competition-defence trade-off in introduced ranges. Such trait shifts can increase the relative fitness of offspring and completitive advantage beyond tetraploid plants, as well as facilitating invasion success and their rapid spread over tetraploid plants. In China, Solidago canadensis maybe adopt two eco-evolutionary strategies:a combination of pre-adapted traits and rapid adaptive evolution. Rapid evolution during the invasion process in this species is very important to for invasion success, polyploidy does lead to rapid evolution in the process of invasion in Solidago canadensis.