ecosystems lecture 4

ecosystems lecture 4 - Ecosystems (4) The Nitrogen Cycle...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Ecosystems (4) The Nitrogen Cycle And that it was great pity, so it was, This villanous salt-petre should be digg'd Out of the bowels of the harmless earth, Which many a good tall fellow had destroy'd So cowardly; Henry IV Part 1, 1:3 Shakespeare Questions to answer 1. Why is nitrogen commonly a limiting factor? 2. What are the forms in which nitrogen occurs? 3. What fluxes move nitrogen from the atmosphere to the biosphere? What controls their rates? 4. What fluxes move nitrogen from the biosphere back to the atmosphere? What controls their rates? 5. What fluxes move nitrogen between plants and the soil & water? What fluxes occur just in the soil or water? 6. What fluxes move nitrogen from the land to the water? 7. How have humans altered the nitrogen cycle? why is this a problem? Living things are constantly surrounded by Nitrogen… Gaseous composition of the Earth of the Earth’s atmosphere So why does it frequently limit growth?? Ecosystems Lecture 4 1 Accessing atmospheric Nitrogen is energetically expensive; not everyone can get to it! Energy requirement to break bond (kJ/mol) N N ~942 C C ~346 NITROGEN POOLS Atmosphere 1.9% of global total nitrogen N2 Water 0.4% biosphere N (N2) Terrestrial N <<0.1% River flow ROCK 97.8% of global N Schlesinger 1997 Biogeochemistry AIR NITROGEN FIXATION N2 + 8H+ + 16ATP Nitrogen gas + energy nitrogenase PLANTS SOIL WATER 2NH3 + H2 + 16ADP ammonia Symbiotic bacteria – Rhizobium and Frankia Free-living organisms: •Aerobic soil bacteria (many) •Anaerobic soil bacteria (many) •Cyanobacteria (marine and fresh waters) Anabaena circinalis Rhizobium trifolii http://commtechlab.msu.edu/sites/dlc-me/zoo/zdrr0101.html Ecosystems Lecture 4 http://www.nies.go.jp/biology/mcc/images/digital_camera/0006.jpg 2 AIR SYMBIOTIC N-FIXERS PLANTS SOIL Rhizobium Bacteria form nodules on legume roots Peltigera canina N-fixing lichen Cyanobacterial symbiont WATER Azolla, a water fern, being added to Vietnamese rice fields Others: • Frankia on a variety of plants (bayberry, alders, others) • Termites – bacteria in the gut • Shipworms – bacteria in a gland in the gut Longleaf pine savannas (Pinus palustris) Southeastern U. S. Frequent fires Low N in soils Most diverse plant community in North America (50 species/m2) 43 species of legumes AIR Nitrogen Deposition on Grasslands PLANTS SOIL WATER Mean number of species per 4 m2 plot Total N deposited (kg N/ha/yr) Stevens et al. Science 303: 1876-1879 2004 Ecosystems Lecture 4 3 The Haber-Bosch Process: Industrial N fixation N2 (g) + 3 H2 (g) ⇌ 2 NH3 N2 gas: from air H2 gas: synthesized from methane http://wapedia.mobi/thumb/7ef4502/en/max/470/720/Haber-BoschEn.svg?format=jpg%2Cpng%2Cgif Galloway et al. 2003 NITROGEN FLUXES Atmosphere N Fixation Deposition Denitrification Biomass burning NH3 gas loss Denitrification N Fixation Deposition Water Terrestrial N River flow ROCK Schlesinger 1997 Biogeochemistry Ecosystems Lecture 4 4 AIR PLANTS Denitrification: NO3+ + Organic C WATER SOIL ANOXIA (Nitrate) NO N2O N2 (Nitric (Nitrous (N2 gas) oxide) oxide) Agricultural Treatment Wetland, China Created wetlands Ohio Controls on denitrification rate • Anoxia (remember it’s a reduction reaction!) • Nitrate supply supply • Organic carbon supply HOUSE + SEPTIC TANK 7.1 FOREST 15.9 21.4 38.5 stream 16.3 6.3 5.7 4.8 DENITRIFICATION RATE KG NITROGEN ( as N 2O gas) / HECTARE / YEAR AIR Peter Groffman and colleagues GROFFMAN JEQ 23:917 Ecosystems Lecture 4 PLANTS WATER SOIL 5 INTERNAL CYCLE OF N PLANT litterfall uptake Plants ORGANIC N SOIL NO3- Soil nitrification mineralization NH4+ immobilization Leaching to groundwater AIR PLANTS surface water WATER SOIL C:N ratio (litter quality) controls N mineralization rate Joshi et al. 2004 Organic N -C-C-NH2 Substrate C:N vs. Microbial C:N NH4+ microbes Low C:N NH4+ release to soil mineralization High C:N immobilization Ecosystems Lecture 4 6 C:N RATIOS OF COMMON MATERIALS MATERIAL RANGE OF Atoms C:Atoms N 6:1 - 12:1 Microbial tissues Sewage sludge Sewage sludge 5:1 – 14:1 14 Soil humus 10:1 – 12:1 Animal manures 13:1 – 25:1 Legume residues 13:1 – 25:1 Plant residues, straw 60:1 – 80:1 Wood, sawdust 150:1 – 600:1 From: Stevenson 1986 Cycles of Soil. Wiley. ORGANIC N SOIL NO3- mineralization NITRIFICATION: nitrification NH4+ immobilization Nitrosomonas: NH4+ + O2 NO2- + 2H+ + H2O ammonium + O2 nitrite Nitrobacter: NO2- + O2 NO3Nitrite + O2 nitrate OVERALL: Ammonium nitrite nitrate IMMOBILIZATION: microbes retain nitrogen for their own use (creating more microbes) NH4+ supply is the main control on nitrification rate Hammersly et al. 2002 Ecosystems Lecture 4 7 INTERNAL CYCLE OF N PLANT litterfall uptake Plants ORGANIC N SOIL NO3- Soil mineralization nitrification NH4+ immobilization Leaching to groundwater AIR PLANTS surface water WATER SOIL Concentration (mg N/liter) Leaching of nitrogen from land to water: Glassboro, NJ 30 20 Limit for health 10 mg/L 10 0 New urban Old Agriurban culture Forest AIR PLANTS WATER SOIL Stackleberg, USGS WRI 97- 4241 NITROGEN FLUXES Atmosphere N Fixation Deposition Denitrification Biomass burning NH3 gas loss Denitrification N Fixation Deposition Uptake Litterfall Water Terrestrial N River flow Mineralization Immobilization Nitrification Mineralization Immobilization Nitrification ROCK Schlesinger 1997 Biogeochemistry Ecosystems Lecture 4 8 ...
View Full Document

Ask a homework question - tutors are online