Legumerhizobium human intervention combustion offuels

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Unformatted text preview: the forest burns, the peat burns, too Human effects on carbon budget • Larger carbon compounds oxidized to CO2, released into atmosphere • Current annual rates of CO2 release: – Fossil fuel burning ~ 6 billion tonnes – Deforestation ~ 1.6 billion tonnes – (Review carbon cycle figure) • Atmospheric [CO2] from 280 ppm to 393 ppm • Strengthening the “greenhouse effect” N cycle Mostly gaseous, compounds highly soluble, minimal sedimentary pools Limiting steps involve converting inert N2 gas, which plants can’t use, into usable soluble nitrate or ammonium. (Legume‐Rhizobium) Human intervention: Combustion of fuels, use of energy to make synthetic fertilizers 4 27/03/2013 Nitrogen chemistry 101 • N fixation reduces N2 to NH3, requires much energy • N fixation done mostly by eubacteria, cyanobacteria, some by lightning – especially Rhizobium and legume plants Human intervention in nitrogen cycle • An atmospheric cycle (fast) • Anthropogenic “reactive” N inputs from fuel combustion now exceed natural production rates (in industrial areas, rainwater is now a dilute fertilizer) • Nitrification converts NH4+ to NO3‐ (nitrate) • Ecosystems being enriched • Denitrification converts NO3‐ to N2 • We can make N fertilizers by fixing N2, using electricity or natural gas P cycle Gases not important, most compounds minimally soluble, sedimentary pools dominate, ends up in ocean sediments Limiting steps involve “weathering” of rock...
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This note was uploaded on 03/31/2013 for the course BIO 101 taught by Professor Profans during the Spring '13 term at Case Western.

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