Geochemical Nutrient Scavenging. High mountain lakes as model systems. Research Questions

Transcription

1 Research Questions Geochemical Nutrient Scavenging High mountain lakes as model systems Kurt Hanselmann, Microbiology: Ecology: Biogeochemistry: Geobiology: How do microorganisms cope with low nutrient concentrations? Are oligotrophs extremophiles? Which are the major ecological determinants influencing microbial communities adapted to lownutrients? What is the role of erosion particle surfaces as nutrient scavengers in high-mountain oligotrophic habitats? How do microbes mediate iron and phosphorus cycling? 2 Growth of Cyanobacteria on erosion particles Contents 3 4

2 Sizes of erosion particles from top sediment layer Adsorption and release of ammonia from clay cumulative mass finer [%] p 8 % < 0.2 µm 47 % > 0.2 and < 2 µm 22 % > 2 and < 5 µm 3 % > 5 µm equivalent spherical diameter [µm] Contents Where do the nutrients originate? Nutrients of atmospheric origin Nutrients of lithospheric origin Nutrients of biospheric origin 7 8

3 Nutrients from rock erosion Dissolution of P and Fe containing minerals Dissolution of Hydroxyapatite - a source for phosphate Ca 0 (PO 4 ) 6 (OH) HCO 3-0 CaCO H + 6 HPO H 2 O Dissolution of Ankerite - a source for iron Fe x Mg y Ca z (CO 3 ) x+y+z + (x+y+z) H + xfe 2+ + ymg 2+ + zca 2+ + (x+y+z) HCO O 2 Marino Maggetti, Fribourg FeOOH, Fe 2 O 3 dissolves hydroxyapatite rusty surface varnish on rocks 9 0 Nutrients from remote locations transported via the atmosphere Long range transport of particles Annual distribution of Saharan dust events at JFJ 2002/2003 M. Collaud Coen, et al. Atmos. Chem. Phys. Discuss. 3, ,

4 Dust events are most common during summer Fertilizing by rain Contents of major ions in rain Rain peak fraction Rain washout fraction Ammonia + NH 4 [mg/m 3,ppb] Nitrate - NO 3 [mg/m 3, ppb] Sulfate 2- SO 4 [mg/m 3, ppb] Phosphate 3- PO 4 [mg/m 3, ppb] < 0. < 0. Conductivity [µs/cm] ph Schwarzenbach, K., Masters Thesis, 994 / Confin 3 4 Contents Jöri Lake XIII A model system for studying the biogeochemical iron cycle and its role in ecosystem evolution Jöri I, II and III Jöri XIII - S Jöri XIII - N 5 6

5 Iron cycling is a dominant process Geobiological processes in iron cycling Caroline Amberg - Brunner, What is it? Why is it the way it is? What is it? Why is it the way it is? 9 20

6 What is it? Why is it the way it is? Iron mediated processes in Jöri Lake XIII Norbert Swoboda, Seasonal Phosphate and iron release and entappment Seasonal N/P ratios changes Gabriela Iqba l- Nava, 2003 Gabriela Iqba l- Nava,

7 Iron and phosphate cycling during ice cover period Iron and phosphate cycling during ice free period Coupled iron - phosphate cycle in earth history High productivity in low-nutrient environment 27 28

8 Contents Preparation of nutrient containing iron oxyhydroxide coated particles Fe Fe P relative intensity Si P relative intensity K 0.2 Ca Fe 0.2 K Fe energy [kev] energy [kev] Matthias Wagner, Producing Fe-P i -oxide covered particles (acc. to Wagner M., 2000) P/Fe ratios in artificial precipitates # phosphate/iron /sulfate /silicate / potassium / sodium / calcium - ratios in solution 3 CO 2 /N 2 first, then compressed air gas out stirrer ph electrode ice for cooling Precipitation of iron-phosphate-oxide: Ultrapure deionized water buffered with 0 mm NaHCO 3 Gassing with CO 2 /N 2 (9:) until ph < 7 Add 235 µm KH 2 PO 4 (sampling) Add.07 mm FeSO 4 * 7H 2 O Add particles Gassing with compressed air until the reaction is finished and ph is stable 32 / > / / / / / / / P/Fe in precipitate,4,2 0,8 0, ,4 6 0, P/Fe in solution 3 Matthias Wagner, 999

9 Leaching erosion particles from sediments Contents species [µmol/l] experiment Na-Dithionite extraction aqueous leaching aqueous leaching 2 Fe 2+ Ca 2+ Mg 2+ Na + K + NH 4 + NO 3 - PO 4 3- SO nm.797 nm nd nd < < CaCl 2 extraction 0.59 nm nm nm < Nm = not measured nd = not detected Matthias Wagner, Low nutrient concentrations preferentially support growth of cyanobacteria Growth on uncoated Fe ox or Fe ox +P coated particles biomass wet [mg] Biomass wet weight [mg] High nutrient medium (80 µs/cm, left). Low nutrient medium (5 µs/cm, right). Growth as biofilm for 30 days. Blue: filamentous cyanobacteria, yellow: other organisms, left columns: beginning of experiment right columns: end of experiment total wet weight of biomass [mg] Fe: Fe-oxyhydroxide- coating without phosphate Fe/P: Particles coated with Feoxyhydroxide-phosphate complexes Reactor run with medium devoid of P, for 62 days, conductivity 2 µs/cm. blue: filamentous cyanobacteria, yellow: other micro-organisms left column beginning, right column end of experiment 0 TPN 05 Philipp Roelli, 200 NM 0 Without Fe or P Fe Fe/P Philipp Roelli,

10 Microbial growth on iron-phosphate-oxides Growth on Fe-P i -oxides Solubility Fe 2+ in anoxic pore water: ~0-3 M Fe 3+ in equilibrium with ferrihydrite: < 0-8 M Blank: no iron, no phosphate, no inoculum Blank: no iron, no phosphate, inoculum (Jöri XIII-sediment) Iron-oxide, no phosphate, inoculum (Jöri XIII-sediment) Iron-phosphateoxides, inoculum (Jöri XIII-sediment) P i Fe(III) Microbial Fe(III) reduction Fe(II) P i P i Nutrient-poor medium, no phosphate, no iron Anoxic conditions (CO 2 /N 2 -atmosphere) Fe 2+ and phosphate determination Fe(III) Fe(II) P i Caroline Amberg - Brunner, Bacteria growing on Fe-P i -surfaces Biofilm on Fe-P i coated particle Caroline Amberg - Brunner, 2002 Caroline Amberg - Brunner, 2002 Sample M5 Gram-stained magnification 630x Sample 32 DAPI-stained magnification: 000x 39 40

11 Geobacter metallireducens Contents Live/Dead-stained 000x magnification Caroline Amberg - Brunner, Direct contact between cell and iron oxide Ligand-mediated Fe-dissolution Iron-reducing bacteria in culture generally attach to the iron oxides (Thamdrup, 2000) Reductive dissolution mechanism (Lovley and Woodward, 996) Cytochrome c may be involved in electron transport to Fe(III) (Straub et al., 200) chelator Fe(II) Fe(II) e - Fe(II) Fe(III)oxide chelator Fe(III) Fe(III) Fe(III) oxide 43 44

12 Use of siderophores (Neilands, 98) Humic substances Humic substances serve as electron shuttle (Lovley et al., 996) AHQDS OH SO 3 H Fe(II) HO 3 S OH Fe(II) + 2e H + -2e - - 2H + O SO 3 H AQDS = 2.6- anthraquinone disulfonate HO 3 S O AQDS AHQDS = 2.6- anthrahydroquinone disulfonate Can Iron be oxidized anaerobically? Yes! -Phototrophic Iron Oxidation Contents First discovered by Widdel and colleagues in 993 Fe(II) is electron donor for photosynthesis Supplied a mechanism for anaerobic Fe oxidation Authors proposed this might be involved with formation of BIF s exciting thought Widdel et al Nature 362: Ehrenreich and Widdel AEM 60: Straub et al., 996. AEM 62: