Dandan Cheng

Increasing evidence has confirmed the importance of plant-associated bacteria for plant growth and productivity, and thus it is hypothesized that interactions between bacteria and alien plants might play an important role in plant invasions. However, the diversity of the bacterial communities associated with invasive plants is poorly understood. We therefore investigated the diversity of rhizospheric and endophytic bacteria associated with the invasive annual plant Senecio vulgaris L. (Asteraceae) based on 16S rRNA gene data obtained from 57 samples of four Senecio vulgaris populations in a subtropical mountainous area in central China. Significant differences in diversity were observed between plant compartments. Specifically, the rhizosphere harbored many more bacterial operational taxonomic units and showed higher alpha diversity than the leaf and root endospheres. The relative abundance profiles of the bacterial community composition differed substantially between the compartmen...

Satellite imagery has been widely used to monitorthe extent of environmental change in both mine andpost mine areas. This study uses Remote sensing and GeographicalInformation System techniques for the assessmentof land use/land cover dynamics of mine relatedareas in Wa East District of Ghana. Landsat satellite imageriesof three different time periods, i.e., 1991, 2000 and2014 were used to quantify the land use/cover changes inthe area. Supervised Classification using Maximum LikelihoodTechnique in ERDAS was utilized. The images werecategorized into five different classes: Open Savannah,Closed Savannah, Bare Areas, Settlement and Water. Imagedifferencing method of change detection was used toinvestigate the changes. Normalized Differential VegetativeIndex valueswere used to correlate the state of healthyvegetation. The image differencing showed a positive correlationto the changes in the Land use and Land coverclasses. NDVI values reduced from 0.48 to 0.11. The landuse change matrix...

Invasive plants colonize new environments, become pests and cause biodiversity loss, economic loss and health damage. Senecio vulgaris (Common groundsel, Asteraceae), a cosmopolitan weed wildly distributes in the temperate area, is reported with large populations in the north–eastern and south–western parts, but not in southern, central, northern or north-western part of China. We studied the germination behavior of S. vulgaris to explain the distribution and the biological invasion of this species in China. We used seeds originated from 12 populations in native and invasive range (six populations in each range) to conduct germination experiments in a climate chamber and ambient condition. When incubated in climate chamber (15°C) seeds from the majority of population showed >90% germination percentage (GP) and the GP was equal for both ranges. The mean germination time (MGT) was significant different among the populations. Under ambient conditions, significant effect of range, st...

Invasive plants escape from some natural enemies as predictions of Enemy Release Hypothesis (ERH). However, in fact they still have to face the pressure of generalist herbivores in introduced ranges resulting in the maintenance or enhancing of resistance ability to generalist herbivores. In this study, we carried out a general feeding bioassay in a laboratory with leaves of Senecio vulgaris to test the difference in resistance between ranges. White jade land snails (WJLD, Achatina fulica) were fed with the leaves of Pakchoi (Brassica chinensis), Lettuce (Lactuca sativa), native and invasive plants of S. vulgaris. The feeding experiment with S. vulgaris leaves was carried out in two waves. We found that both native and invasive S. vulgaris plant were resistant again to WJLD compared to Pakchoi and Lettuce. However, there were no significant differences between native and invasive plants of S. vulgaris in relation to the resistance against WJLD. The results prove the maintenance of ch...

Pyrrolizidine alkaloids (PAs), a typical kind of secondary metabolites in plants, have important roles on defense against herbivores and pathogens; however, specialist herbivores adapted to PAs can use them as cues for oviposition and feeding. Thus, in the native ranges, PA diversity and concentration in plants were selected by the balance between pressure from generalist and specialist herbivores. In introduced ranges, where the specialist herbivores are absent, the introduced plants could increase concentration and diversity of PAs. This predication is deduced from the Shift Defense Hypothesis (SDH). In this research, we investigated whether there were any differences between native and invasive Senecio vulgaris plants (from Europe and China, respectively) with regards to the PA composition and concentration. We grew the native and invasive S. vulgaris plants in an identical condition and harvested them when they started to bloom. Their roots and shoots were separately harvested a...

According to the Evolution of Increased Competitive Ability (EICA) hypothesis and Enemy Release Hypothesis (ERH), comparing the plants from the same species, individuals from the invasive range will outperform those from the native range. However, not all recent studies support the prediction of these two hypotheses. In this study, we sought to test the prediction by comparing the performance of common groundsel ( Senecio vulgaris ) taken from native (Europe) and invasive (China) ranges. Those plants were grown in a greenhouse and in a common garden, and harvested with various vegetative and reproductive traits measured. We found that although the plants grown in the common garden grew and reproduced better than those grown in the greenhouse, the invasive plants outperformed the native plants in relation to most vegetation parameters (except plant height) and reproduction in both experiments; and generally, the invasive plants allocated more proportion of biomass to root than the na...

Invasive plants colonize new environments, become pests and cause biodiversity loss, economic loss and health damage.Senecio vulgarisL. (Common groundsel, Asteraceae), a widely distributing cosmopolitan weed in the temperate area, is reported with large populations in the north–eastern and south–western part, but not in southern, central, or north-western parts of China. We studied the germination behavior ofS. vulgaristo explain the distribution and the biological invasion of this species in China. We used seeds originating from six native and six invasive populations to conduct germination experiments in a climate chamber and under outdoor condition. When incubated in a climate chamber (15 °C), seeds from the majority of the populations showed >90% germination percentage (GP) and the GP was equal for seeds with a native and invasive origin. The mean germination time (MGT) was significantly different among the populations. Under outdoor conditions, significant effects of origin,...

Biological invasion is regarded as one of the greatest environmental problems facilitated by globalization. Some hypotheses about the invasive mechanisms of alien invasive plants consider the plant–herbivore interaction and the role of plant defense in this interaction. For example, the “Shift Defense Hypothesis” (SDH) argues that introduced plants evolve higher levels of qualitative defense chemicals and decreased levels of quantitative defense, as they are released of the selective pressures from specialist herbivores but still face attack from generalists. Common groundsel (Senecio vulgaris), originating from Europe, is a cosmopolitan invasive plant in temperate regions. As in other Senecio species, S. vulgaris contains pyrrolizidine alkaloids (PAs) as characteristic qualitative defense compounds. In this study, S. vulgaris plants originating from native and invasive ranges (Europe and China, respectively) were grown under identical conditions and harvested upon flowering. PA com...

Because increasing evidence has confirmed the importance of plant-associated bacteria for plant growth and productivity, it is believed that interactions between bacteria and alien plants play an important role in plant invasions. However, the diversity of bacterial communities associated with invasive plants is poorly understood. Therefore, we investigated the diversity of rhizo- and endophytic bacteria associated with the invasive annual plant Senecio vulgaris L (Asteraceae) based on bacterial 16S rRNA gene data obtained from 57 samples of four S. vulgaris populations in a subtropical mountainous area in central China. Significant differences in diversity were observed between plant compartments. Rhizosphere harbored much more bacterial OTUs and showed higher alpha diversity than the leaf and root endosphere. Bacterial community composition differed substantially between compartments and locations in relative abundance profiles, especially at phyla and family level. However, the t...

The diversity of secondary metabolites (SMs) has been poorly understood from both a mechanistic and a functional perspective. Hybridization is suggested to contribute to the evolution of diversity of SMs. In this paper we discuss the effects of hybridization on SMs and herbivore resistance by evaluating the literature and with special reference to our own research results from the hybrids between Jacobaea vulgaris (syn. Senecio jacobaea) and Jacobaea aquatica (syn. Senecio aquaticus). We also review the possible genetic mechanism which causes the variation of SMs and herbivore resistance in hybrids. Most SMs in hybrids are present in the parents as well. But hybrids may miss some parental SMs or have novel SMs. The concentration of parental SMs in hybrids generally is constrained by that in parental plants, but transgressive expression was present in some hybrids. Hybrids may be as susceptible (resistant) as the parents or more susceptible than the parents, but rarely more resistant than the parents. However, different hybrid classes (F1, F2, backcrossing and mixed genotypes) show different patterns in relation to herbivore resistance. The variation in SMs and herbivore resistance occurring in hybrids could be explained by complicated genetic mechanisms rather than a simple one-gene model. Most previous work in this field only reported mean trait values for hybrid classes and few studies focused on genotype differences within hybrid classes. Our study in Jacobaea hybrids showed transgressive segregation in most SMs and herbivore resistance. To summarize, our article shows that hybridization may increase the variation of SMs and affect herbivore resistance, which may partially explain the evolution of chemical diversity in plants.

Secondary metabolites such as pyrrolizidine alkaloids (PAs) play a crucial part in plant defense. PAs can occur in plants in two forms: tertiary amine (free base) and N-oxide. PA extraction and detection are of great importance for the understanding of the role of PAs as plant defense compounds, as the tertiary PA form is known for its stronger influence on several generalist insects, whereas the N-oxide form is claimed to be less deterrent. We measured PA N-oxides and their reduced tertiary amines by liquid chromatography-tandem mass spectrometry (LC-MS/MS). We show that the occurrence of tertiary PAs is not an artifact of the extraction and detection method. We found up to 50% of tertiary PAs in shoots of Jacobine - chemotype plants of Jacobaea vulgaris. Jacobine and its derivatives (jacoline, jaconine, jacozine and dehydrojaconine) may occur for more than 20% in reduced form in the shoots and more than 10% in the roots. For 22 PAs detected in F(2) hybrids (J. vulgaris × Jacobaea aquatica), we calculate the tertiary amine percentage (TA%=the tertiary amine concentration/(tertiary amine concentration+the corresponding N-oxide concentration) × 100). We found that the TA% for various PAs was genotype-dependent. Furthermore, TA% for the different PAs were correlated and the highest correlations occurred between PAs which share high structural similarity.