Biogeochemical cycles

Transcription

1 Biogeochemical cycles Microbial Ecology SS Biogeochemistry The study of the exchange of material between the living and nonliving components of the biosphere. The biogeochemical cycling of nutrients involves the physical transportation and its chemical and biochemical transformation (Jjemba 2004) Reservoir: An amount of material, defined by certain biological, chemical or physical characteistics (eg. CO 2 in the atmosphere, S in rocks). Flux: Amount of material that is transfered from one reservoir to another per unit time. Source and sink: Refer to the flux out of or into a reservoir Turnover time: duration it will take to empty the reservoir in the absencce of sources if the sink remains constant. 1

2 Biogeochemistry Biosphere Earth s natural environment can be devided into: Atmosphere (air) Pedosphere (land) Lithosphere Hydrosphere (ocean) 2

3 Elements or compounds do not exist or cycle individually but rather always interact and overlap with other geochemical cycles. Most important cycles: C, O, N, P, S (and Fe) Simplified molecular composition of living material The Redfield-ratio: C 106 :H 263 :O 110 :N 16 :P 1 :(S 1 ) Carbon mean oxidation state CO 2 +IV Carbon dioxide C 4 H 6 O 5 +I Malic acid C 6 H 12 O 6 0 Glucose, Biomass, Acetate C 2 H 5 OH -II Ethanol CH 4 -IV Methane Nitrogen NO - 3 +V Nitrate NO - 2 +III Nitrite N 2 0 Nitrogen NH + 4 -III Ammonium R-NH 2 -III Amines Reduction Reduction Oxidation Oxidation Sulfur SO 4 +VI Sulfate S 2 O 3 +II Thiosulfate S o 0 Sulfur H 2 S -II Sulfide R-SH -II Sulfhydryl-group Reduction Oxidation 3

4 Carbon cycle The central nutrient cycle: Determination of the amount of CO 2 in the atmosphere, as well as rate of microbial turnover of organic matter. Includes all life and inorganic C reservoirs. Organic carbon constitue a relatively small reservoir of carbon, most are carbonate minerals Microorganisms play important role in regulating the pools. Particulate organic matter Dissolved organic matter Particulate organic carbon Dissolved organic carbon POM DOM POC DOC Carbon pools Much of the carbon on Earth is tied up inorganically in the form of carbonates (limestone and dolomite) about g Another great fraction is trapped as aged organic matter (Bitumen, coal, natural gas, petroleoum) about g Unaged dead material g Living biomass g Carbon on the atmosphere g Living systems depend on unaged, dead organic matter and atmospheric carbon In order not to exhaust this carbon, it has to be recycled 4

5 Carbon cycle Carbon mean oxidation state CO 2 +IV Carbon dioxide C 4 H 6 O 5 +I Malic acid C 6 H 12 O 6 0 Glucose, Biomass, Acetate C 2 H 5 OH -II Ethanol CH 4 -IV Methane Reduction Oxidation Primary production: +IV 0 CO e H + <CH 2 O> + H 2 O Photo- and chemo autotrophic organisms e.g. Calvin-cycle, reverse TCA, reductive AcetylCoA- cycle, 3-Hydroxypropionate Cycle 5

6 Carbon cycle Photosynthetic Primary production CO 2 + H 2 O! <CH 2 O> + O 2 Stochiometry 1:1:1:1 The biggest syntrophic relation of all living creatures runs via biological loops... CO 2 + H 2 O " <CH 2 O> + O 2 Consumption (remineralisation) Primary production = Consumption + deposition Composition of plant litter Sugar (15%) direct uptake and utilization by many organisms Hemicellulose (15%) polysaccharide, decomposed by bacteria and fungi Cellulose (20%) large molecule, transformed by bacteria and fungi into glucose Lignin (40%) complex, insoluble, toxic, large molecule; degraded by fungi and actinomycetes to sugars, carboxilic acids, ammino acids, degradation depends on oxygen. Waxes (5%) and phenols (5%) are less abundant, minor role in C cylce, hardly degradable = long turnover time 6

7 Carbon cycle Carbon cycle within the biosphere 7

8 Carbon mean oxidation state CO 2 +IV Carbon dioxide C 4 H 6 O 5 +I Malic acid C 6 H 12 O 6 0 Glucose, Biomass, Acetate C 2 H 5 OH -II Ethanol CH 4 -IV Methane Reduction Oxidation 8

9 Overall processes of anoxic decomposition Nitrogen cycle The Redfield-ratio: C 106 :H 263 :O 110 :N 16 :P 1 :(S 1 ) N # 10 % of dry biomass As nitrogen represent a biolimiting element in many environments it plays a central role in controlling biological productivity. Microbial reclycling of nitrogen is essential for life! Nitrogen is the most abundant gas in the atmosphere (79 %) 9

10 Nitrogen species mean oxidation state of nitrogen NO - 3 +V Nitrate NO - 2 +III Nitrite N 2 0 Nitrogen NH + 4 -III Ammonium R-NH 2 -III Amines Reduction Oxidation Oxidation state of nitrogen in all organic compounds is - III N-Assimilation: - Nitrogen fixation (endergonic process) N H 2 + 2H + 2 NH Ammonification NO e H + NH H 2 O 10

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12 Examples of microorganisms from the nitrogen cycle Pseudomonas denitrificans reduces nitrate to nitrogen (when no oxygen is available)! Denitrification, anaerobic respiration Many Cyanobacteria (e.g. in heterocystes) and bacteria reduce nitrogen to ammonia. Important symbiotic nitrogen fixing microbes are Rhizobia who live in Wurzelknöllchen of plants. Anabaena with heterocyst Nitrosomonas oxidizes ammonia to nitrite (first step catalysed via Oxygenase with O 2 as electron acceptor)! chemolithotrophic process Nitrococcus oxidises nitrite to nitrate (O 2 as electron acceptor)! chemolithotrophic process 12

13 Wurzelknöllchen: Symbiosis of plants with nitrogen-fixing bacteria S-cycle S # 1 % of dry mass Dissimilatoric processes are more important than assimilatoric processes many reactions only catalysed by prokaryotes sulfate (SO 4 ) most oxidised form (marine: 28 mm) 'sulfide' (H 2 S) most reduced form (toxic) Sulfur (S), sulfite (SO 3 ), thiosulfate (S 2 O 3 ) and tetrathionate (S 4 O 6 ) important intermediates Reduced S-compounds serve also as electron donators for anoxygenic phototrophic bacteria 13

14 Important sulfur compounds H-S-H, H-S - - S-S-S-S - S-S-S S S S-S-S "sulfide" poly sulfide O - O-S-O - O O - O-S-S - O - O=S O - S8-sulfur sulfate thiosulfate sulfite O O O - O-S-S-S-O - O O trithionate O O - O-S-S-S-S-O - O O tetrathionate 14

15 Sulfur cycle mean oxidation state of sulfur SO 4 +VI sulfate S 2 O 3 +II thiosulfate S o 0 sulfur H 2 S -II sulfide R-SH -II sulfhydryl-group Reduction Oxidation S-assimilation: - assimilatory sulfate reduction (endergonic process) SO H 2 + 2H + H 2 S 2 ATP 2 ADP 15

16 Aerobic sulfide oxidation respiratory process (O 2 oder NO 3- ) (sulfur oxidising bacteria, SOB) SO 4 oxic anoxic HS - Achromatium oxaliferum, A sulfur oxidising bacterium with intra cellular sulfur dropplets and Calcium carbonate crystals Aerobic sulfide oxidation (incomplete sulfide oxidation) SOB SO 4 S 2 O 3 S o oxic anoxic Thiomagerita namibiensis, A sulfur oxidising bacterium with intra cellular sulfur dropplets HS - 16

17 SO 4 S 2 O 3 S o oxic anoxic Thiosulfate reduction sulfur reduction, anaerobic respiration (SRB, sulfur reducers, Iron reducers, thiosulfate reducers) HS -, FeS, FeS 2 Phototrophic sulfur bacteria in the hypolimnion of lake Dagow SO 4 oxic SO 4 S 2 O 3 S o h!" anoxic Anaerobic sulfide oxidation, Photosynthesis process (Green and red sulfur bacteria) HS - 17

18 Thiosulfate- and sulfur disproportionation Anaerobic fermentation SRB S 2 O 3 + H 2 O SO 4 + HS - + H + 4 S o + 4 H 2 O SO 4 + 3HS - + 5H + SO 4 S o oxic anoxic S 2 O 3 HS - 18

19 Examples of microbes from the sulfur cycle Desulfovibrio desulfuricans reduces sulfate to sulfide! Desulfurication, anaerobic respiration Pyrobaculum reduces sulfur to sulfide (with peptides as electron donator) at >100 C! Hyperthermophilic sulfur reducing Archaeon, anaerobic respiration (?) Chlorobium oxidises sulfide (via sulfur) in the light to sulfate and uses die reduction equivalents for the reduction of CO 2! anoxygenic photosynthesis, photolithoautotrophic process Sample from lake Dagow with anoxygenic phototrophic bacteria Thiobacillus oxidises sulfide and other reduced sulfur compounds to sulfate (O 2 as electron acceptor) and reduces CO 2! chemolithoautotrophic process 19

20 Iron- and manganese-cycle Iron- and manganese reduction Geobacter sp. Shewanella sp. Fe 3+ Mn 4+ Fe 2+ Mn 2+ Iron oxidation Manganese oxidation Arthrobacter sp., Bacillus sp. Acidophilic iron oxidiser Acidithiobacillus ferrooxidans Leptospirillum ferroxidans Neutrophilic iron oxidiser Gallionella ferruginea Leptothrix discophora Leptothrix sp. Gallionella ferruginea schematic illustration iron stems grown on Mn 2+ brown: MnO 2 -precipitates 20

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22 P-cycle Phosphate does not run through redox cycles as the other elements mentioned before. However, the availability of phosphat is dependant on the redox state. Phosphate precipitates with oxidised iron as hardly soluble FePO 4 Precipitation of phosphate in a waste-water treatment plant If FePO 4 gets into anoxic conditions, Fe3+ is reduced to Fe 2+ and it becomes soluble and is released again 22

23 The greenhouse effect Solar radiation (mainly short wavelength): 30% returned to outerspace by reflection 51% absorbed by ocean and land 19% absorbed by atmospheric gases Atmospheric gases retain a significant fraction of solar radiation Emission of this energy (as heat) warms up our atmosphere = steady-state temperature is determined by gas content Once gases had absorbed radiation, steady-state would be established at an elevated temperature 71% of infrared light emitted from Earth is absorbed by one of the atmospheric gases: Atmosphere temperature rise if infrared-absorbing gases increase, including methane and nitrous oxide Connection of atmospheric and marine carbon cycle Why does the marine carbon cylce play such an important role in regulating global climate? 23