Biogeochemistry of N NREM 665

Transcription

1 Biogeochemistry of N NREM 665

2 N Biogeochemistry I. Forms of N Oxidation State Phase/Form Ammonium, NH + 4 Ammonia, NH 3 Molecular nitrogen, N 2 Nitrous oxide, N 2 O Nitric oxide, NO Nitrite, NO - 2 Nitrogen dioxide, NO 2 Nitrate, NO - 3 2

3 II. N Cycling Processes A. Plant Uptake: Plants assimilate N both above & belowground 1. N uptake highly hl variable: ƒ(species, i soil, nutrient t status, t climate) a. N of plant tissue inversely correlated to biomass: dilution & distribution, w/ age 2. Tissue N:P (mass) < 15 N limitation, N:P > 15 P limitation 3

4 B. N Fixation: in aerobic & anaerobic conditions (favored in low O 2 ) conversion of N 2 to NH 3 by organisms via the enzyme nitrogenase N - +8H + +8e ATP 2NH 3 +H ADP + 16Pi N 2 1. N N 2. Energy (ATP) requirement for Nfix is high, can be higher than 16 ATP shown above 3. Free-living soil bacteria (e.g. Klebsiella, Azotobacter), Cyanobacteria (blue-green algae), symbiotic root nodules of leguminous plants (genus - Rhizobium) all perform N fix 4

5 N-fixation in cyanobacteria 5

6 N-fixation by Rhizobium spp. Nodules in Trifolium subterraneum 6

7 Controls on N Fixation in Wetlands DOM + Mo availability + Reducing conditions Fe availability + + Microelements Macroelements Oxygen - N Fixation DIN Low N:P in recycled nutrients Low N:P loading (Howarth et al. 1989) 7

8 N Fixation Rates in Wetlands N Fixation Rate Ecosystem (mg N m -2 day -1 ) Reference Coastal wetlands Buresh et al Rice paddies 2-48 Buresh et al FW marshes Howarth et al Cypress swamps 1-8 Howarth et al Peat bogs Howarth et al Oligotrophic lakes 0-5 Howarth et al

9 C. NH 3 Volatilization: Complex process mediated by physical (temperature, wind speed, H 2 O depth), chemical (ph, NH 3 conc), biologial (PSN-algae consume CO 2 & ph, plant density) factors 1. ph > 8, NH 3 dominant & will volatilize from water column NH 4+ + OH - H 2 O + NH 3 9

10 2. Controls on Ammonia Volatilization in Wetlands Amm monia vo olatilization low high low high low high NH 3 concentration Water depth Plant density low high low high low high Temperature Wind speed Soil CEC (Reddy & DeLaune 2008) 10

11 D. Mineralization: in aerobic & anaerobic conds, conversion of org N to NH 3 as OM is decomposed NH 2 CONH 2 + H 2 O 2NH 3 + CO 2 11

12 E. Nitrification: in aerobic conditions NH 4+ oxidized in 2 steps 1. Nitrosomonas: 2NH O 2 2NO H 2 O + 4H + + energy 2. Nitrobacter: 2NO 2- + O 2 + 2NO 3- + energy 3: What do both require? F. Denitrification: in anaerobic conditions, facultative bacteria convert NO 3- to molecular N C 6 H 12 O 6 + 2NO 3-6CO 2 + 6H 2 O + N 2 1. microbes breathing NO 3- instead of O 2 2. DNT inhibited in acid ph, low temp, low C envs 12

13 Reductive Nature of DNT 13

14 Hole in the pipe model NH NO 3 N 2 Nitrification Denitrification (Adapted from Firestone & Davidson 1989) 14

15 Controlling Factors for Different Scales Scale Organism Field/Site Landscape Regional Global Controlling Factors O 2, NO 3, C Soil H 2 O, NO 3 supply, C supply Soil type, Plant community type Geomorphology, Land use Biome type, Climate (Adapted from Groffman 1991) 15

16 G. Anammox: anaerobic ammonium oxidation, newly discovered N process in a WWTP in 1994 NO NH 4+ N 2 + 2H 2 O 1. involves nitrite not NO 3-, aerob/anaer interface where DNT limited by low C 2. anammoxosome unusual lipid = site of rxn 3. observed in WWTP, WW lagoons, marine & estuarine sediments, taro a. In marine sed, anammox can prod up to 67% of N 2 (Thamdrup & Dalsgaard 2002) 16

17 Anammox Typical porewater N profile from a deep ocean sediment indicating the zone of anaerobic ammonium oxidation (Engström et al. in prep) 17

18 Anammox in Hawaii taro sediments The highest anammox populations occurred in samples flooded for at least 6 months (samples 1, 4, 5, 6, 7), whereas the dry taro field (sample 2) & the newly flooded field (3) showed lower anammox populations o (Deenik unpublished data). 18

19 Conditions for N transformations Soil Conditions Process Aerobic Anaerobic N Fixation YES YES NH 3 Volatilization YES YES Mineralization YES YES Immobilization/ Uptake YES YES Nitrification YES NO Denitrification NO YES Anammox NO YES 19

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21 (Mitsch & Gosselink 2007) 21

22 N Budget for Thoreau s Bog (Hemond 1983) 22

23 Fluxes of N in wetlands + - (Bowden 1987) 23

24 III. N removal pathways in wetlands A. Short term: immobilization, uptake by herbaceous plants, algae, periphyton 1. B. Long term: denitrification, anammox, uptake by woody plants 24

25 IV. N Biogeochemistry Summary A. Dominant Processes: Plant Uptake: Assimilation of NH 4+ & NO 3- into biomass B. N Fixation: Conversion of gaseous N 2 to NH 3 Ammonia Volatilization: NH 4+ NH 3 &lossofnh of 3 to atmo. Mineralization: Decomposition of or.g N compounds Nitrification: Oxidation of NH 4+ to NO 3 - Denitrification: Conversion of NO 3- to N 2 Anammox: NH 4+ + NO 2- N 2 + H 2 O 25