Nitrogen Biological Cycle Characteristics of Seepweed(Suaeda salsa) Wetland in Intertidal Zone of Huanghe(Yellow) River Estuary

From April 2008 to November 2009,the nitrogen(N) cycle of plantsoil system in seepweed(Suaeda salsa) wetland in the intertidal zone of the Huanghe(Yellow) River estuary was studied.Results showed that soil N had sig-nificant seasonal fluctuations and vertical distribution,and the net N mineralization rates in topsoil were significantly different in growing season(p < 0.01).The N/P ratio(9.87 ± 1.23) of S.salsa was less than 14,indicating that plant growth was limited by N.The N accumulated in S.salsa litter at all times during decomposition,which was ascribed to the N immobilization by microbes from the environment.Soil organic N was the main N stock of plant-soil system,accounting for 97.35% of the total N stock.The N absorption and utilization coefficients of S.salsa were very low(0.0145 and 0.3844,respectively),while the N cycle coefficient was high(0.7108).The results of the N turnovers among compartments of S.salsa wetland showed that the N uptake amount of aboveground part and root were 7.764 g/m2and 4.332 g/m2,respectively.The N translocation amounts from aboveground part to root and from root to soil were 3.881 g/m2 and 0.626 g/m2,respectively.The N translocation amount from aboveground living body to litter was 3.883 g/m2,the annual N return amount from litter to soil was more than 0.125(-) g/m2(minus represented immobilization),and the net N mineralization amount in topsoil(0-15 cm) in growing season was 1.190 g/m2.The assessment of N biological cycle status of S.salsa wetland indicated that N was a very important limiting factor and the ecosystem was situated in unstable and vulnerable status.The S.salsa was seemingly well adapted to the low-nutrient status and vulnerable habitat,and the N quantitative relationships determined in the compartment model might provide scientific base for us to reveal the special adaptive strategy of S.salsa to the vulnerable habitat in the following studies.

The permeability effect of microcystin-RR on Escherichia coli and Bacillus subtilis

Microcystins are a kind of cyclic hepatoxins produced by many species of cyanobacteria.Most previous work have been done on the toxic effects of microcystins on animals and plants.However,the reports about the effect of microcystins on microbial cells are very limited.In this work,the permeability of MC-RR on the cell outer membrane of Escherichia coli(E.coli) and Bacillus subtilis(B.subtilis) was discussed.The permeability effect of MC-RR on the cell outer membrane of E.coli and B.subtilis under different concentrations was demonstrated by a rapid and sustained reduction in the A675 values of lysozyme-treated cells.The decrease of the absorbance values showed a time-and dose-effect.The extravasations of protein and carbonhydrate increased with the increment of the treated-concentration of MC-RR.The results showed that MC-RR could increase the permeability of cell outer membranes of E.coli and B.subtilis.The synergistic effects of MC-RR and lysozyme on bacteria indicated that MC-RR might play an ecological role in bacteria in combination with other substances in some aquatic environments.