Dynamics And Controlling Factors Of Trace Elemental Composition Of Micro-organisms And Particles In Seawater

Trace elements such as Cu and Mo are essential in the growth and metabolism of bacteria and algae in the ocean.Previous researchers have mainly focused on dissolved metals,but little on trace elements in micro-organisms,and especially on the interactions between cellular elements and micro-organisms.Recently accumulative evidence shows that there exists a large difference of trace element composition among different microbial cells,which possibly dictates the microbial growth and metabolism.However,as far as I konow the dynamics and controlling factors of trace elemental composition(such as Cu,Mo and Fe)in micro-organisms have not been reported yet.In order to explore how trace elements participate and affect microbial metabolism,I mainly carried out three experiments in the following:(1)Laboratory manipulative culture experiments.We conduced a series of cultures of micro-organisms(such as Thiobacimonas profunda JLT2016(Sulfur-oxidizing bacteria,SOB),Synechococcus sp.WH 7803 and Nannochloropsis oceanica);(2)Mesocosm experiments in Wuyuan Bay.I mainly investigated the effects of key environmental factors(CO2)on microbial growth and cellular elements composition,and explored the dynamics of trace element composition in phytoplankton and in situ bacteria along with hydrochemical parameters;(3)Field investigation on particulate trace element composition(including micro-organisms)in Jiulong River estuary and shallow-vents off Kueishan Island.The main results are listed as follows:(1)No significant differences of trace element composition were observed in the eukaryotic algae(Photoautotrophy)(Nannochloropsis oceanica:Mo(4.6 ± 0.6 ?mol/L),Cu(41 ± 1 pmol/L);Algae average(Ho et al.,2003):Mo(3.1 ± 0.8 ?mol/L),Cu(35 ±31 ?mol/L?.Instead,I did find significant differences of trace element composition in different types of micro-organisms such as Nannochloropsis oceanica and Synechococcus,which belonged to eukaryotes and prokaryotes,respectively.The concentrations of trace elements in Synechococcus(Mo(122 ± 5 ?mol/L),Cu(1027 ±125 ?mol/L))were all higher than those of Nannochloraopsis oceanica[Fe(13± 2 mmol/L),Mn(1167 ± 62 ?mol/L)].(2)Chemoautotrophic states of microbes are characterized with higher cellular Mo and Cu(Mo(2004 ± 168 ?mol/L,Cu(2812 ± 927 ?mol/L))than photoautotrophic states[Mo(122 ± 5 ?mol/L),Cu(1027 ± 125 ?mol/L)].Photoautotrophic states are characterized with higher Mn and Fe[Mn(67±6 mmol/L),Fe(1081±157 mmol/L)]than chemoautotrophic state[Mn(2.8±0.7 mmol/L),Fe(183±2 mmol/L)].The SOB has higher cellular trace element concentrations(Mo:2004 ± 168 ?mol/L;Sr:92 ± 1 mmol/L;Mn:2857 ± 698 ?mol/L;Fe:1081 ± 157 mmol/L)than heterotroph(Mo:1019± 207 ?mol/L;Sr:18 ± 4 mmol/L;Mn:479 ± 7 ?mol/L;Fe:25 ± 8 mmol/L)in chemoautotrophic state.(3)By modelling the dynamics of elemental composition,I found that SOB absorbed dissolved metals from ambient waters quickly at the initial stage(Cu:chemoautotrophic:4.6×10-18?16.1×10-18 mol/cell;heterotrophic:3.8×10-18?11.2×10-18 mol/cell),then decreased with the increase of cell abundance.And the cell abundance(X)and cellular trace element content(M)varied dynamics as following the equations below:(?)The model was successfully applied in analyzing the biological growth and metabolism,and the absorption and consumption of trace metals.In addition,the mesocosm experiments showed that CO2 would affect the trace element composition of micro-organisms.The trace element content of algae was higher in the initial and exponential stages of growth in the high CO2 environment(HC:1000 ppm)(2 d,Fe:54 mmol/g Chl-a(HC),41 mmol/g Chl-a(LC);Mn:7.1 mmol/g Chl-a(HC),3.0 mmol/g Chl-a),while the elemental contents of the in situ bacteria were higher in the low CO2 environment(400 ppm)(2 d,Fe:143188 × 10-18 mol/cell(LC),32066 × 10-18 mol/cell(HC);Mn:6995 ×10-18 mol/cell(HC),2765 ×10-18 mol/cell).Conclusively,I suggested that the absorption during growth and biological dilution process are two key processes affecting the composition of microbial cell elements.(4)Field investigations show that dissolved Fe distribution in the Jiulong River was lower than the conservative mixing line between freshwater seawater endmembers,while Mn and Cu was higher,suggesting of a net removal of Fe but a net addition of Mn and Cu existing locally.The Fe,Mn and Cu,which are strong in particle activity,gradually decreased from upstream to downstream,and most of them were adsorbed and removed in the estuary area,and some of them are transported in the form of paticles.While Mo is not easy to be removed by particles,the dissolved state gradually increased fro upstream to downstream.The particulate Fe concentration was significantly larger than dissolved Fe[Dry season:382-3057 ?mol/L(Particulate),13-35 ?mol/L(Dissolved);Wet season:483-11293 ?mol/L(Particulate),115-2994 ?nol/L(Dissolved)].Dissolved Mn concentrations were significantly larger than particulate Mn[Dry season:60-1694?mol/L(Dissolved),42-359?mol/L(Particulate);Dry season:248-5388?mol/L(Dissolved),150-682?mol/L(Particulate)].Flux calculations show that oceanic Fe fluxes(Fe:2.4 x 108 mol/yr)was significantly higher than that in the dry season(Fe:3.2 x 107 mol/yr)[the discharge fluxes(F=C x Q,C:Total element(Dissolved element+particulate element)]in the Jiulong River estuary,while particulate trace element(Fe,Mn and Cu)could contribute to a large fraction in their total oceanic fluxes(Fe:90.6%;Mn:65.7%;Cu:85.9%during the dry season).(5)The investigation in the hydrothermal vents show that these hydrothermal eruption carries large amounts of particulate matter and elements into the nearby waters.Particularly,I observed that the concentrations of particulate trace elements in the Yellow Smoker were lower(except Mo)than in the White Smoker.Excess of Fe,Mn and Cu was observed in the opening of Yellow Smoker(Fe:397 nmol/L;Mn:2.4 nmol/L;Cu:1.1 nmol/L),which may be attributed to the precipitation under the conditions of increased pH and decreased temperature.The addition of trace elements in these regions may be one of the causes of biological abundance increases.We compared Jiulong River estuary with shallow-vents off Kueishan Island,and found the discharge flux in the Jiulong River estuary area was significantly larger than that of Kueishan Island,which was above 6 orders of magnitude.This study combined laboratory manipulative culture experiments with field investigation,which explored the absorption and utilization of trace elements by micro-organisms,along with the adsorption and desorption process in the natural environment(estuarine and hydrothermal area).This study supports the deep exploration of marine ecology and biogeochemical significance of trace elements.