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Microbial communities and global change

Microbial communities and global change. David Lipson, Ph.D Professor, Department of Biology San Diego State University dlipson@sciences.sdsu.edu. The 3-Domain System. Based on ribosomal RNA gene sequences. Almost all life is microbial! The diversity of microorganisms is vast.

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Microbial communities and global change

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  1. Microbial communities and global change David Lipson, Ph.D Professor, Department of Biology San Diego State University dlipson@sciences.sdsu.edu

  2. The 3-Domain System Based on ribosomal RNA gene sequences Almost all life is microbial! The diversity of microorganisms is vast “crown group” of Eukaryotes, includes animals, plants and multicellular algae

  3. Microbial Communities • Control Global Biogeochemistry • diverse, mostly uncultured • Not well understood

  4. Elevated atmospheric CO2

  5. Possible Microbial feedbacks in global change Plant community change ? Plant growth Nutrient mineralization _ _ + Warming Microbial trace gas production + + CO2 increase Microbial Respiration Red = positive feedback (destabilizing) Green = negative feedback (stabilizing) Purple = uncertain

  6. Methane (CH4) • About 1.7 ppm in atmosphere • Strong greenhouse gas • Important in ozone chemistry

  7. Atmospheric methane is increasing in the industrial age…

  8. But why?

  9. (aerobic) (anaerobic) CO2 respiration C fixation Organic C methanogenesis Methanotrophy (methane oxidation) CH4 (methane)

  10. Methanogens (Archaea) Methanopyrus sp. Methanococcus jannaschii

  11. Trichonympha, symbiotic protist in termite gut, with its own symbiotic methanogens

  12. Agriculture and Methane production • Rice paddies: • Projected to increase by 70% in next 25 years • Anaerobic, rich in organic C – leads to methane production • Some oxidiation occurs due to O2 conducted by rice plants into rhizosphere • Effect of N fertilization: • Stimulate plant and methanogen growth • Inhibit methane oxidation (in most studies of upland rice and other ecosystems…)

  13. Competitive inhibition of methane oxidation by ammonium H H C H H H N+ H H H Ammonium Methane

  14. However, in one recent study… In rice paddy soils, ammonium additions stimulated CH4 oxidation – methanotrophs were N limited Bodelier et al. 2000 Depends on CH4 and N availability – lots of CH4 in rice paddy, overcomes competitive inhibition

  15. Nitrous oxide (N2O) • About 300 ppb in atmosphere • Strong greenhouse gas: 200X worse than CO2. • lifetime=150 years. • Contributes to stratospheric ozone depletion (after conversion to NO, nitric oxide)

  16. NOx in fossil fuel emissions Clean air act However, N2O concentration still increasing by 0.3% /year

  17. Global N cycle (Units are 1012g/year)

  18. Rough global N2O budget • Oceans 2.0 • Soils • Tropical 3.7 • Others 2.0 • Fertilized agriculture 0.7 • Land use change 0.7 • Biomass burning 2.2 • Total sources 11.3 • Reaction with O3 10.5 • Atmospheric increase 3.0 • Total sinks 13.5 (1012 g N/yr)

  19. Simplified N cycle anaerobic N fixation N2 NH4+ (by-products of nitrification) N2O (N2O, NO) Organic N denitrification ammonia oxidation (nitrification) NO2- NO3- nitrite oxidation (nitrification) aerobic

  20. nitrifiers Nitrosococcus Nitrosolobus Nitrospina Nitrosospira Nitrosomonas

  21. Agriculture and Nitrous oxide N2O NH3 NO3- N2O “leaky pipe” model More N fertilization leads to more NOx emissions

  22. Hall and Matson 1999 N additions stimulate NOx emissions in P-limited tropical forest

  23. N saturation vs. N limitation • Most temperate ecosystems N limited, but tropical forests often P limited • Tropical forests biggest natural source of N2O • Globally, 2.2 Tg N/year deposited from fossil fuel burning. • Eventually, systems become saturated, start leaking N

  24. Eutrophication Nutrients lead to bloom, algae decompose, use up oxygen

  25. Effect of fertilizer runoff on denitrification in coastal areas • Off coast of India during monsoon season: • N in runoff causes eutrophication of coastal waters • Lower oxygen leads to increased denitrification (Naqvi et al. 2000)

  26. Altabet et al. 2002 Over the last 60,000 years in the Arabian Sea, temperature, CO2 and denitrification are correlated (Isotope data: 15N related to denitrification)

  27. Hypothesized denitrification control over global climate after last glacial maximum (~22,000 ya) High denitrification rates in ocean Lower NO3- in ocean Lower production rates in ocean Slower CO2 removal by ocean Climate warms

  28. Coccolithophores (Haptophyta) Emiliana huxleyi

  29. Nutrient limitation in Oceans Nutrient limitations depend on community: algae, cyanobacteria, diatoms

  30. Dinoflagellates N limited in oceans

  31. Cyanobacteria N2 fixers Iron (or P) limited in oceans

  32. Diatoms Silica limited

  33. Most Fe, P, and Si in ocean comes from land Arroyo formed during huricane Nora

  34. The Iron hypothesis Increased iron transport from land (more dust) led to increased ocean productivity, lowered atmospheric CO2 in last glacial maximum (18,000 years ago) Let’s dump iron into the ocean and save the world! John Martin (1935-1993) “Give me half a tanker full of iron and I’ll give you the next ice age” • Arguments against: • • Silica has slower half-life, limits diatom production, fits data better (8000 y lag after dust decreased) • • Evidence that P controls N fixation in oceans • • Much spatial variability, limitations depend on conditions and community

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