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Hangzhou, China

Yang R.,Anhui Normal University | Yang R.,Zheeiang University | Zan S.,Anhui Normal University | Tang J.,Zheeiang University | Chen X.,Zheeiang University
Shengtai Xuebao/ Acta Ecologica Sinica

Invasion of habitats by non-native species is one of the major factors that threaten global biodiversity and ecosystem functioning. China is becoming one of the most severely invaded countries in the world with increasing frequency of deliberate species introduction, international tourism and worldwide trade of agricultural products. A comprehensive understanding of invasion process and involved mechanism is very necessary to avoid the outbreak of invasive species and prevent new invasion. Solidago canadensis L, the worldwide invader with a invasion history over 70 years in China, has been extensively studied in the last decades. However, few studies concerned the persistent and profound impacts on local environment induced by invasion, and their feedbacks on subsequent invasion and plant community dynamics. Here, we reviewed the successful invasion mechanisms of S. canadensis from its biological characteristics, invasibility of the introduced range, allelopathic effect and plant-soil feedbacks based on novel interests and recent advancements, analyzed and evaluated the inherent relations between four aspects above. It suggested that invasion was a complicated biological process that involved multitrophic interactions of herbivores, carnivores, plants and decomposers, and a result of interactions between multiple mechanisms, among which the most far reaching reason was disturbance by human activities. The strong vegetative propagules produced by rhizome of S. canadensis strengthened its population established in invaded habitat, and the numerous fertile offspring expanded new habitat through wind dispersal. The high phenotype plasticity to resource fluctuation and high tolerance to stress conditions offered extra advantages over local competitors. These extrinsic performance could partially be explained by intrinsic features as S. canadensis was a polyploid complex and characterized by high genetic diversity. Moreover, the strong allelopathic effects on native plants and soil borne pathogens significantly inhibited potential antagonists, which undoubtedly further extended its dominance. Susceptibility of the introduced range resulted from appropriate climate, low biotic resistance and strong human disturbance provided favorable conditions for invasion. Besides, facilitated by mycorrhizal mutualism also played an important role in the invasion of S. canadensis. Community structure of arbustracular mycorrhizal fungi was changed in a way that favored S. canadensis more than native host plants. The mechanism of host preference remained unclear and represented an intriguing field that awaited to be intensively studied. Up to now, however, enemy release from goldenrod specific gallmaker and other pathogens in China did not show any positive impacts on its growth and reproduction. Although parasitized by Cuseuta japoniea exhibited an obvious biological control potential, its ecological risks need to be further examined and evaluated before extensive application. Prospects for the study of S. canadensis in the future were proposed with emphases on (1) isolation, structure determination and in situ acting mechanism illumination of allelochemicals; {2) establishment and improvement of database, population dynamic and spreading tendency prediction using mathematical models; (3) long term monitoring on post invasion environmental changes, study on functions of S. canadensis in ecosystem and co-evolution with local organisms and (4) proper utilization, effective control and eradication method of S. canadensis. Source

Zhu Z.-C.,Zheeiang University | Shan G.-R.,Zheeiang University
Acta Polymerica Sinica

Controlled/living radical polymerization ( CLRP) is one of the most rapidly developing areas in polymer science, and among the various existing technique, nitroxide-mediated polymerization ( NMP) was the first to be proposed. Most researches focused on the development of aliphatic nitroxide while few studies were devoted to the use of aromatic nitroxides in NMP. This paper describes nitroxide-mediated radical polymerization of methyl methacrylate ( MM A ) in the presence of 4, 4 '-dimethoxydiphenyl nitroxide ( DMDPN) and azobisisobutyronitriie ( AIBN ) . The aromatic nitroxide was synthesized by oxidation of 4 ,4'- dimethoxydiphenyl amine with oxone under biphasic conditions ( CH2Cl2/H20) in rapid and good yields. The bulk polymerization of MMA was conducted in sealed glass tubes at different conditions. The polymerization kinetics was monitored by gravimetric method while the molecular weight and its distribution of poly ( methyl methacrylate) ( PMMA ) synthesized were determined by gel permeation chromatography. The effects of the nitroxide/initiator ratio and polymerization temperature on thepolymerization kinetic, molecular weight and polydispersity index ( PDI ) of PMMA were investigated in detail, and reinitiation reaction experiment was conducted to veriiy the chain-end activity. The results showed that in this polymerization system, as the DMDPN allows delocalization of the single electron through the aromatic ring, the side reaction of β-H transfer from the propagating macro radicals to the free nitroxide which would hinder the propagating process, was neglected and the chain propagation in MMA polymerization could be efficiently controlled. Molecular weight of PMMA increased linearly with monomer conversion at diferent DMDPN/AIBN ratios and temperatures which was diferent from common radical polymerization. The PMMA could be reinitiated which showed the characteristics of controlled/living radical polymerization. The polymerization rate was quite fast at low DMDPN/AIBN ratios and an induction period appeared when the ratio was too high. At the DMDPN/AIBN ratio of 1. 6, the PDI was the lowest and the curve of ln( M 0/M) versus time was a straight line which crossed the coordinate origin. The polymerization rate increased and PDI decreased as the polymerization temperature increased. MMA polymerization could even been operated at 70 °C though the PDI was relative higher. Source

Chen R.,Zheeiang University | Luo J.,Zheeiang University | Lu Y.,Zheeiang University | Yu L.,Zheeiang University | And 6 more authors.
Acta Polymerica Sinica

In this study hyperbranched polyacetals ( HBPAs) were used as a new type of porogens to prepare porous biodegradable microspheres. HBPAs were synthesized through the transacetalization process , which was carried out with an AB 2 type monomer of 4-( 2-hydroxyethoxy ) -benzaldehyde dimethyl acetal and a B2 type core of benzaldehyde dimethyl acetal catalyzed with pyridinium camphorsulfonate ( PCS ) . The results demonstrated that HBPAs were highly pH sensitive. They degraded rapidly at pH 5. 0 , and barely degraded at pH 7. 4. The porous biodegradable pol (lactic acid ) ( PLA) microspheres were prepared by blending HBPAs and PLA with the emulsion-solvent evaporation method and the blending microspheres were then placed in acidic conditions for 2 weeks. As HBPAs hydrolyzed faster than PLA , the HBPAs component was first degraded from the blending microspheres to form small pores in the PLA matrix. DSC results and degradation process of the blending microspheres showed that the phase separation appeared in the blending microspheres of HBPAs and PLA. This phase separation favored the hydrolysis of HBPAs in the blending microspheres. The pore size of the microspheres can be regulated by changing the weight ratio of HBPAs to PLA. With increasing the HBPAs amount, the pore size of the PLA microspheres increased in a linear manner. HBPAs, as a new type of porogens, offer a new method to prepare porous microspheres. Source

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