Ye Linlin

Progress and prospect of research on cyanobacteria nitrogen fixing in aquatic ecosystem

The predominance of nitrogen fixing cyanobacteria in the eutrophic aquatic systems is related to many environmental factors,such as nutrient forms and concentrations,nitrogen to phosphorus ratio,water temperature and trace metal.The nitrogen fixing cyanobacteria dominated in lakes with the concentration of orthophosphate above 0.01mg / L,the concentration of dissolved inorganic nitrogen under 0.1 mg / L,furthermore,the lower ratio of nitrogen to phosphorus was suggested to indicate the occurrence of the nitrogen fixing cyanobacteria,but the differentiation mechanism of nitrogen fixing and non-nitrogen fixing cyanobacteria need a deep research.Moreover,cyanobacteria nitrogen fixing rates can be influenced by the light availability,inorganic nitrogen concentrations,heterocyst abundance and the fixed nitrogen determines the contribution to the pools of nitrogen.The nitrogen fixing cyanobacteria is the important contributor to the pools of nitrogen in the ocean systems,but in the eutrophic lakes,its contribution is still in dispute.Thus,this paper reviewed the researches on nitrogen fixing cyanobacteria to attract attention of scientist on its important contribution to the pool of nitrogen in aquatic systems.

Temporal and spatial distributions of phytoplankton and inorganic and organic nitrogen in northwest region of Lake Taihu

Surface water samples of five sampling sites from the estuary to lake center were collected from October 2012 to October 2013 in the northwest region of Lake Taihu, where with severe cyanobacterial bloom. Water temperature, dissolved oxygen, and bacterial abundance were analyzed, as well as the phytoplankton community, dissolved inorganic nitrogen (DIN) and dissolved or⁃ ganic nitrogen (DON) and nitrogen to phosphorus ratios. The phytoplankton assemblage was mainly composed of Cyanophyta, Ba⁃ cillariophyta, Chlorophyta and Cryptophyta. No significant difference in Cyanophyta cell density was observed, which may be ex⁃ plained by the combined effects of current flow and wind. Cyanophyta biomass contributed to the phytoplankton with the maximum value of 34% ±15% , but Cryptophyta biomass was more than 50% in some sampling sites in spring, suggesting a competition be⁃ tween Cryptophyta and Cyanophyta. The CCA analysis suggested that the distribution of dominant genera was affected by dissolved inorganic and organic nitrogen concentrations, and total nitrogen to total phosphorus ratio.Significant differences in ammonium nitro⁃ gen(NH4 ⁃N) and DIN concentrations were observed among the sampling sites, no significant difference in DON was observed.Uti⁃ lization by Cyanophyta probably caused the decline of concentrations of NH4 ⁃N and nitrate nitrogen(NO3 ⁃N) during summer. Mo⁃ reover, the dynamics of NH4 ⁃N was also affected by the release of NH4 ⁃N from sediment, thus, Cyanophyta cell density correlated more significantly with NO3 ⁃N than NH4 ⁃N. TN ∶TP and DIN ∶TP decreased to the lowest values during Cyanophyta bloom, sugges⁃ ∗ 国家自然科学基金项目( 41201076, 91547119) 资助. 2016 07 16 收稿; 2016 10 05 收修改稿. 叶琳琳 (1981~ ),女,博士,副教授;E⁃mail:yelinlin8164@ 163.com. 860 J. Lake Sci.(湖泊科学),2017,29(4) ting that phytoplankton, especially Cyanophyta may be limited by nitrogen. A significant negative correlation was observed between Cyanophyta cell density and DON, indicating that DON can also be utilized by Cyanophyta during nitrogen limitation.