NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur NRES 201 Biotic Cycling of Nitrogen Sulfur 1 Biotic Cycling of Nitrogen Sulfur Today s lecture topics Nitrogen in plants Natural occurrence of nitrogen Nitrogen in soils The nitrogen cycle Biological fixation Atmospheric deposition Mineralization Immobilization 2 1 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Plant nutrient concentrations Source Havlin et al 1999 3 Functions of nitrogen in plants Protein constituent Structural Enzymes Required for all metabolic processes Inheritance Constituent of DNA and RNA Energy storage and transfer Constituent of ATP and related compounds Photosynthesis Constituent of chlorophyll 4 2 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Functions of nitrogen in plants Protein constituent Structural Enzymes Required for all metabolic processes No life without N Inheritance Constituent of DNA and RNA Energy storage and transfer Constituent of ATP and related compounds Photosynthesis Constituent of chlorophyll 5 Natural occurrence of nitrogen N occurs in all four spheres of the earth Lithosphere Atmosphere Hydrosphere Biosphere Source Stevenson 1982 6 3 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Natural occurrence of nitrogen N occurs in all four spheres of the earth Lithosphere Atmosphere Hydrosphere Biosphere About 98 is in the lithosphere As fixed NH4 in igneous rocks Source Stevenson 1982 The rest is mainly in the atmosphere Air is 78 N2 by volume The ultimate source of N for living systems 7 Nitrogen in soils Total content Surface soil 0 06 0 3 N 1200 6000 lb A 6 Subsoil 0 02 N Organic soil up to 3 5 N Organic forms of N 95 of total N in most surface soils Derived from living organisms Inorganic forms of N Typically 2 5 of soil N Major forms 8 4 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur The nitrogen cycle Source Havlin et al 2005 9 Biological nitrogen fixation Overall reaction N2 NH4 organic N High energy requirement A triple bond N N must be broken Two forms Symbiotic N2 fixation By legumes And a few nonlegumes Nonsymbiotic N2 fixation By free living bacteria Source http www slideshare net 10 5 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Symbiotic N2 fixation Legumes Associations with Rhizobium or Bradyrhizobium Fixation occurs in root nodules Source Brady and Weil 2004 11 Symbiotic N2 fixation Legumes Associations with Rhizobium or Bradyrhizobium Fixation occurs in root nodules Amount of N fixed varies widely Fixation reduced by Soil acidity Plant stress NO3 availability Legumes take up soil N Source Tisdale et al 1993 12 6 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Nonlegumes Observed for 100 plant species from 7 families Many are trees or shrubs that form nodules with the actinomycete Frankia Colonize infertile or disturbed soils Lower fixation than with nodulated legumes An alder root nodule Source http en wikipedia org 13 Nonsymbiotic N2 fixation Major organisms Photoautotrophs Mainly blue green algae Important in rice paddies Heterotrophs Such as Azotobacter Source http www kvkphek nic in Significance Very limited because of the need for Light Organic C Fertilizer sales 14 7 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Atmospheric nitrogen deposition Forms of deposition As NH4 or NO3 In particulates dry deposition In rain or snowfall wet deposition Sources of deposition Manure Combustion of fossil fuel Natural fires Lightning Magnitude of deposition Source http www fws gov Typically 1 20 lb A per yr Greatest near animal feedlots and urban areas 15 Mineralization Defined as Organic N NH4 Significance The most important N cycle process for plant growth Without N2 fixation In the absence of N fertilization Source http filebox vt edu On fertilized soils Opens access to soil reserves of organic N Provides an ongoing supply of mineral N 16 8 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur During the first decade of cultivation the prairie soil was apparently too rich for wheat the wheat tended to grow too tall and then fall over or lodge thus reducing grain yields L F Welch 1979 17 A process of decomposition Decomposition occurs in stages C and N are liberated as waste products C as CO2 N as NH4 Carried out by a wide variety of heterotrophs Fungi Actinomycetes Bacteria Source Stevenson 1986 18 9 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Key fraction of soil N is alkali labile Decomposable by NaOH Probably derived in part from amino sugars which occur In bacterial cell walls In actinomycete spores In fungal hyphae as chitin Estimated by the Illinois soil N test ISNT Source http www australianscience com au 19 Promoted by Favorable environmental conditions Adequate soil moisture Warm temperatures 100 F optimal Good aeration Absence of soil acidity Wetting and drying cycles Drying kills some soil microbes Upon rewetting the survivors utilize the dead biomass The result is a flush of mineralization 20 10 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Cultivation Improves aeration Exposes fresh organic matter to microbial attack N fertilization Accelerates residue decomposition Unless P or S is limiting Source https www pioneer com 21 Immobilization Defined as NH4 NO3 organic N A process of assimilation The reverse of mineralization except that either NH4 or NO3 may be immobilized NH4 is strongly preferred over NO3 Both processes may operate simultaneously 22 11 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur Carried out by heterotrophic microbes The same ones that carry out mineralization Promoted by Warm temperatures Adequate soil moisture Absence of soil acidity Presence of carbonaceous residues Temperature effects on immobilization much greater for NO3 than for NH4 Because of the need for mineralizable C which is required for immobilization of NO3but not NH4 23 Effect of the C N ratio of organic amendments Source Havlin et al 2005 24 12 NRES 201 Lectures 35 37 Fall 2014 Biotic Cycling of Nitrogen Sulfur The C N ratio decreases during decomposition because CO2 is lost NH4 is not lost Source Havlin et al 2005 25 Biotic Cycling of Nitrogen Sulfur Today s lecture topics Nitrogen in plants Natural occurrence of nitrogen Nitrogen in soils The nitrogen cycle Biological fixation Atmospheric deposition Mineralization Immobilization 26 13