1. Ecology Hierarchy, Productivity, Biogeochemistry

33. Biogeochemical Cycling The movement of macronutrients through the earth’s systems Pools (sinks) Fluxes (rates) Retention times

34. The biggest pool is not shown

35. 70 million GT of C

50. Nitrogen Cycle Processes Fixation Assimilation Ammonification Nitrification Denitrification

51. Nitrogen Fixation N 2 -> NH 4 + Requires anoxic conditions Occurs only in prokaryotes in : Soil, Legume nodules, and cyanobacteria

52. Nitrogen Assimilation NH 4 + -> amino acids --> protein, nucleotides etc. -> Requires anoxic conditions Occurs only in plants

53. Ammonification Organic Nitrogen (amino acids, protein, nucleotides) -> NH 4 + Decay Many many bacterial species, fungi and other heterotrophs

54. Nitrification A two step process both bacterially mediated NH 4 + + O 2 --> NO 2 - + O 2 --> NO 3 - -> Requires oxygen-rich conditions First reaction mediated by Nitrosamonas spp. Second Reaction mediated by Nitrobacter spp.

55. Denitrification NO 3 - --> N 2 or NO 3 - --> N 2 O -> Requires anoxic conditions Mediated by Pseudomonas spp. & Bascillus spp.

61. Rhizobium

75. Alvin Woods Hole Oceanographic Institute MIT