Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

At least two distinct trade-offs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How different seasonally tied herbivore assemblages simultaneously affect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large fish in summer from below-ground herbivory by Bewick’s swans in winter. We measured the individual and combined effects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory effect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal effect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative effect on Zannichellia palustris, but the effect size differed considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above- and below-ground herbivory may each stimulate different components of a macrophyte community as they each favoured a different subordinate plant species

Effect of Silver Nanoparticles in a Hydroxyapatite Coating applied by Atmospheric Plasma Spray

In this study, 0.5, 1, 3, and 5 % nano-silver containing hydroxyapatite coatings (nAg-HA) on a Ti6Al4V substrate were developed by atmospheric plasma spray (APS), and their antibacterial efficiency was evaluated in the following bacterial strains: Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The optimal operating parameters for the coatings application were determined by online diagnostic of thermal HVOF- and plasma spraying processes. Scanning electron microscopy (SEM) showed that both micro and nano-silver (Ag) particles were distributed on the coating surface. The antibacterial efficiency was studied according to the JIS Z2801:2000 standard Antimicrobial products-Test for antimicrobial activity and efficacy. The results show that the antibacterial efficiency of a 1 % nAg-HA coating against Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas aeruginosa strains was above 99 % antibacterial rate. Silver ion release tests show that the coatings did not deliver the silver ions in the phosphate buffered saline solution, which generate good cytotoxic properties. The antibacterial mechanisms observed in the coatings are based in the combination of the two following theories proposed by Cao: 1) Disruption of transmembrane proton electrochemical gradient, and 2) bacterial charging process. The electrochemical test in SBF solution at 25 and 37 degrees C showed an i(corr) higher than 25.00E-6 A/cm(2), which justified the good antibacterial properties. The nAg-HA coatings developed presented excellent bond strength (35 MPa in average), nano-mechanical properties, and the failure mode was identified as adhesion-cohesion. This study opens perspectives for the development of in-vivo tests of the nAg-HA coatings applied by APS; research in an alternative method to enhance the nano-particles dispersion into the HA matrix; and finally, the study suggests further research to determine which of the two mechanisms proposed by Cao presents the major effect in the antibacterial rate.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES