Allelopathy confers an invasive Wedelia higher resistance to generalist herbivore and pathogen enemies over its native congener.

The Novel Defense Hypothesis predicts that introduced plants may possess novel allelochemicals which act as a defense against native generalist enemies. Here, we aim to test if the chemicals involved in allelopathy in the invasive plant Wedelia trilobata can contribute to higher resistance against generalist herbivore and pathogen enemies by comparing with its native congener W. chinensis in controlled laboratory conditions. The allelopathic effects of the leaf extract from W. trilobata on the generalist enemies were also assessed. We showed that the larvae of two moth species preferred W. chinensis over W. trilobata. The growth rate of larvae feeding on W. trilobata leaves was significantly lower than those feeding on W. chinensis leaves. When detached leaves were inoculated with phytopathogens, the infected leaf area of W. trilobata was significantly smaller than that of W. chinensis. In addition, the leaf extract of W. trilobata also effectively inhibited the growth of the larvae and the mycelial growth of the phytopathogens. Our results indicate that the defenses of invasive W. trilobata against generalist herbivore and pathogen enemies are stronger than that of its native congener, which may be attributed to the allelopathic effects. This study provides novel insights that can comprehensively link the Novel Defense, Behavioral Constraint and Enemy Release hypotheses. These combined hypotheses would explain how invasive plants escape from their natural specialist enemies, where their allelopathic chemicals may deter herbivorous insects and inhibit pathogen infection.

[Ecological suitability assessment for Notopterygium plants transplanting along altitudinal gradients].

A comprehensive field research had been focused on growing status, underground biomass and active constituents of Notopterygium incisum and N. franchetii to evaluate the ecological suitability and appropriate cultivation zones by growing the two species seedlings along different elevation gradient. The results showed that compared to the survival rate and underground biomass, the beneficial altitude region to N. incisum was ranged from 2 600 m to 4 100 m, while N. franchetii required a lower altitude which ranges from 1 700 m to 3 600 m. For the active constituent contents, the values were higher in the range of 2 600 to 3 600 m for N. incisum, but for N. franchetii, the range was form 1 700 to 3 600 m. This result provides instructional guidance and scientific basis for artificial cultivation of N. incisum and N. franchetii.

[Dynamics of plant biomass and nutrients accumulation of Notopterygium incisum in artificial cultivation].

In this study,field cultivation experiments of Notopterygium incisum had been carried out for three years, and samples had been collected monthly during growth seasons, and biomass and nutrient elements of aerial and underground part of sampled plants had been determined to assess their seasonal and interannual dynamics respectively. The results showed that biomass of underground part (dry weight) increased mainly in the second year after seedling transplanting, i.e., biomass increased about 32 times in the second year whilst less than 6 times and 2 times in the first year and in the third year, respectively. Therefore, efforts for yield improvement should be focused on the first two year in artificial cultivation of N. incisum. Accumulation of nutrient elements increased steady in the underground part during the first and second year, then showed a sharp decline in the first phase of growth season in the third year, while its accumulation in July to August of third year was higher than the value of second year. Ca, Fe, B and Zn were larger demand nutrient elements to meet growth demands whether for the underground part or aerial part during the second year and third year for N. incisum cultivation. This result provided instructional guidance and scientific basis for artificial cultivation and specific fertilizer of N. incisum.

Different Responses of an Invasive Clonal Plant Wedelia trilobata and its Native Congener to Gibberellin: Implications for Biological Invasion.

The invasive clonal plant Wedelia trilobata contains higher levels of ent-kaurane diterpenes, which are precursors of gibberellins (GAs), and higher rates of clonal growth than its native congener W. chinensis in invaded habitats. We hypothesized that the higher levels of endogenous GAs facilitate greater ramet growth in W. trilobata compared with W. chinensis. We quantified endogenous levels of GA1+3 in the two species and compared their growth responses to the changes of endogenous and exogenous GA3 by using short-term and long-term hydroponics experiments. After a period of homogeneous cultivation, levels of endogenous GA1+3 were higher in W. trilobata than in W. chinensis. The reduction of endogenous GAs repressed the emergence of adventitious roots and the growth of W. trilobata in the initial cultivation stage, and inhibited its shoot elongation and biomass. Levels of endogenous GA1+3 were positively correlated with the length of shoots and adventitious roots of W. trilobata. Adventitious roots of W. trilobata also emerged earlier and grew faster when treated with exogenous GA3. In contrast, exogenous GA3 treatment inhibited the length of adventitious roots in W. chinensis, and levels of endogenous GA1+3 did not correlate with shoot or adventitious root length. Our study suggests that GAs accelerate the rapid clonal growth of W. trilobata, more than that of its native congener W. chinensis, illustrating the relationship between plant hormones and the clonal growth of invasive plants. These findings are important for understanding the mechanisms associated with the invasiveness of clonal plants and their potential management.

[Status of wild resource of medicine plant Lamiophlomis rotata and its problems in sustainable use].

OBJECTIVE: Lamiophlomis rotata is a common wild herb in Tibetan traditional medicine with important medicinal and economic value. The paper examines the wild distributions, exploitation regime, and situations. METHOD: A variety of research methods, such as literature survey, specimens inspection, market information collection in major Chinese herbal markets, questionnaire of herbalists and employers of local governments and institutions, and field quadrat survey and AcrGIS as well, have been used for this work. RESULT: Total stock of wild resources of L. rotata is ranging from 3 713.49 tons to 6 896.56 tons (2 519-3 314 t in Qinghai, 490-1 414 t in Gansu, 641-1 167 t in Sichuan, and 422-999 t in Tibet, respectively), acceptable harvest quantity of the herb is ranging from 908-1 675 t per year, and actual harvest quantity is 2 520 t annually far beyond the acceptable harvest quantity. CONCLUSION: Harvesting quantity of L. rotata is far more than that of acceptable, suggesting that utilization pattern of this wild resource plant is unsustainable. L. rotata seems to act as an indicating plant of degraded ecosystem of high-altitude grassland, shrub grassland, and wetland, and distributes in those degraded and degrading plateau ecosystems, and the plant is facing with pressure of ecological protection and wild resource population degradation. Wild population monitoring and standard cultivation are of importance for although they are far from implementation due to shortage of related basic studies.

Different Growth Promoting Effects of Endophytic Bacteria on Invasive and Native Clonal Plants.

The role of the interactions between endophytes and alien plants has been unclear yet in plant invasion. We used a completely germ-free culture system to quantify the plant growth-promoting (PGP) effects of endophytic bacteria Bacillus sp. on aseptic seedlings of Wedelia trilobata and of its native clonal congener W. chinensis. The endophytic bacteria did not affect the growth of W. chinensis, but they significantly promoted the growth of W. trilobata. With the PGP effects of endophytic bacteria, relative change ratios of the clonal traits and the ramets' growth traits of W. trilobata were significantly greater than those of W. chinensis. Our results indicate that the growth-promoting effects of endophytes may differ between invasive and native clonal plants, and the endophytes of invasive plant may be host-specific to facilitate plant invasion.