Biological Nitrogen Fixation Research In Jiaozhou Bay

In this study,the insufficiency of the tracer additional approach in the determination of biological nitrogen fixation rate by the 15N2 isotope tracer was studied.the isotope tracer additional approach which used to determine the nitrogen fixation rate was improved by laboratory experiments,And a more ideal tracer introduction operation was found.On the other hand,there are relatively few reports about biological nitrogen fixation in coastal waters of China.There are no reports on the role of biological nitrogen fixation in the semi-enclosed Jiaozhou Bay Which adjacent to the Yellow Sea.Therefore,It is very important to detect the biological nitrogen fixation rate of water in Jiaozhou Bay area by field investigation experiment and analyse the influencing factors of the biological nitrogen fixation rate combining with other environmental factors.All of these could cover the historical gap in the biological nitrogen fixation research.The 15N2 tracer additional experiment indicates that the degassing of seawater has no effect on the dissolution of 15N2.The background of 14N2 in the no-degassing water will dilute the atom abundance of 15N.The concentration of 15N2 can be reached saturation at 10 min by vortex.The utilization rate of 15N2 was lower and lower as the volume of additional gas increased above the solubility.After the improved operation of direct injection of 15N2 gas into tracer,the atomic percentage of 15N was about twice as high as that by the introduction of the tracer by 15N2 enriched seawater.The operation of improved bubble approach is easy to operate.And reduces the risk of trace metals and nutrient contamination that introduced by 15N2 enriched seawater.At the same time,compared with direct injection of 15N2 gas into tracer,The improved bubble method can accurately determine the concentration of 15N2 in the initial time of the culture and avoid the underestimation of nitrogen fixation rate.In the field application of modified bubble method,the 15N atom percentage of Daya Bay sample is 10.8±1.95%(n=59),and Jiaozhou Bay is 8.00±1.25%(n=46).The atom percentage is higher than that of 15N-enriched seawater.The modified bubble method is easy for operation.The 15N atom percentage in the field experiment relate to 14N2 background and operation skill.Based on the field survey of 4 cruises covering spring summer autumn and winter in Jiaozhou Bay from July 2015 to November 2016.We systematically detect the biological nitrogen fixation rate in Jiaozhou Bay firstly,And reveal the spatial and temporal distribution characteristics of biological nitrogen fixation rate.covering the historical gap in the biological nitrogen fixation research in Jiaozhou Bay.We estimate the contribution of nitrogen fixation to primary productivity by the date during the same voyage.And estimate the contribution of nitrogen fixation to the new nitrogen input of Jiaozhou Bay by literature data.Discuss the regulation mechanism of nitrogen fixation by combining physical hydrological parameters and chemical factors.The following conclusions were obtained from the study of the biological nitrogen fixation rate of.4 voyages:1.The nitrogen fixation rate of different seasons in jiaozhou bay is:Summer(3.1 ?mol N/m3/d)>winter(2.2 ?mol N/m3/d)?spring(2.14 ?mol N/m3/d)>autumn(0.9 ?mol N/m3/d).Volume integrated nitrogen fixation rate:summer(36.0 ?mol N/m2/d)>winter(25.2 ?mol N/m2/d)>spring(17.2 ?mol N/m2/d)>autumn(7.5 ?mol N/m2/d).The volume nitrogen fixation rate in each station is comparable to that reported in China coastal water.2.The nitrogen fixation rate inside the bay during spring,summer and summer is higher than that outside the bay.And the nitrogen fixation rate has a positive correlation with primary productivity.Nitrogen fixation rate is most likely to affected by the DOC which released by primary producer.The correlation between nitrogen fixation and DOC was significant in the fall statistical analysis.The nitrogen fixation rate in Daya Bay was also regulated by DOC during different seasonal cruises from 2015 to 2016.The influence of nitrogen fixation rate on DOC may be universal in coastal water.In winter,the nitrogen fixation rate inside bay is lower than that outside the bay.The distribution of nitrogen fixation rate is consistent with the distribution of water temperature,and the influence of water temperature is obvious.3.The comparison experiment between 15N2 enriched seawater addition and 15N2 bubble addition in Jiaozhou Bay shows that:The biological nitrogen fixation rate detected by 15N2 enriched water incubation is higher than that of 15N2 bubble,which is consistent with the foreign reports.4.The analysis of biologic nifH gene in Jiaozhou Bay in autumn found that the diazotrophs are mainly dominant by proteobacteria.