Associative nitrogen fixation

Assosiative Nitrogen Fixation

1. Associative Nitrogen Fixation

2. Content Introduction Nitrogen source Role of nitrogen in plant Bio-chemistry of nitrogen fixation Mechanism of nitrogen fixation Basic requirement of nitrogen fixation Type of nitrogen fixation Physical nitrogen fixation Chemical nitrogen fixation Biological nitrogen fixation 2

3. Types of biological nitrogen fixers Symbiotic nitrogen fixation Non-symbiotic (Associative) nitrogen fixation Difference between associative & symbiotic Nitrogen fixation Associative Nitrogen fixation (ANF) Importance of associative nitrogen fixation Factors affecting nitrogen fixation Summary References 3

4. Introduction Nitrogen gas are found 78.09% (Wikipedia) on atmosphere of earth. Nitrogen are found in molecular N 2 (N = N) form in soil. Nitrogen fixation is a process by which nitrogen of the Earth’s atmosphere is converted into ammonia (NH 3 ), nitrogen salts or other molecules available to living organisms. 4

5. Nitrogen sources Atmospheric Nitrogen Nitrates, Nitrites and ammonia Amino acids in the soil Organic nitrogenous compounds in insects 5

6. Role of nitrogen in plant Major substance in plants next to water Building blocks Constituent element of Chlorophyll Cytochromes Alkaloids Many vitamins Plays important role in metabolism, growth reproduction and heredity. 6

7. Biochemistry of nitrogen fixation Nitrogen fixation process is given Burris 1966. Nitrogen fixation in atmosphere N 2 is convert into ammonia or nitrates presence in nitrogenase enzyme. Nitrogen fixation in first stable compound is ammonia. Nitrogen convert into ammonia is a reduction. In this process, N 2 is spilt up into free atoms by breaking the triple bond with the help of enzyme nitrogenase. 7

8. This reaction is endergonic (energy consuming) it requires an input of nearly 160kcal energy. N 2 + 160kcal. Nitrogenase 2N Free nitrogen combines with hydrogen forming NH 3 presence of hydrogenate enzyme. The reaction is exergonic (energy releasing) (13kcal, energy). 2N + 3H 2 Hydrogenase 2NH 3 + 13kcal 8

9. Mechanism of nitrogen fixation Nitrogen fixation, natural and synthetic, is essential for all forms of life because nitrogen is required to biosynthesize basic building blocks of plants, animals and other life forms, e.g. -: nucleotides for DNA and RNA and amino acids for proteins. Nitrogen fixation is a process by which nitrogen in the Earth’s atmosphere is converted into ammonia (NH 3 ) or other molecules available to living organisms. Atmospheric nitrogen of molecular dinitrogen (N 2 ) is relatively inert, it does not easily react with other chemicals to form new compounds. 9

10. Basic requirement of nitrogen fixation Nitrogenase and hydrogenase enzymes. Protective mechanism against Oxygen . Ferrodoxin Constant supply of ATP. Hydrogen releasing system or electron donor (pyruvic acid or glucose/ sucrose.) Co-enzyme and cofactors TPP, CoA, Inorganic phosphate and Mg 2+ Cobalt and Molybdenum. A carbon compound 10

11. Type of nitrogen fixation 11

12. Physical nitrogen fixation Physical nitrogen fixation are occur by the natural factor such as, lightening, thunder. It occur in several steps and starts with combination atmospheric discharge and thunder to produce nitric oxide. N 2 + O 2 Lightening Nitric oxide [2NO] 12

13. The nitric oxide is then oxidized to nitrogen peroxide in presence of oxygen. 2NO + O 2 Oxidation Nitrogen peroxide [2NO 2 ] During rains, the nitrogen peroxide combines with rain water to form nitrous acid and nitric acid which come to ground along with rains. 2NO 2 + rain water HNO 2 + HNO 3 On ground the alkali radicals of the react with nitric acid to produce nitrites and nitrates which are soluble in water and which can be absorbed by the plant through roots. Ca +2 or K + salts + HNO 3 soil Ca +2 or K + Nitrates 13

14. Chemical nitrogen fixation Reduction of N 2 into NH 3 by the chemical process is called chemical nitrogen fixation. In the use of Haber’s method. Haber’s process. Haber’s method use of high pressure (nearly 200Atm) and high temperature (nearly 200 C). N 2 + 3H 2 200 ℃/200 atm 2NH 3 The method is used in agriculture and industry. 14

15. Biological nitrogen fixation Fixation of atmospheric nitrogen into nitrogenous salts with the help of micro-organisms. Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. Biological nitrogen fixation in all micro-organisms are prokaryotes. Those micro-organism are called is diazotrophs. 15

16. Types of biological nitrogen fixers Biological nitrogen fixers classified based on fixing micro-organism. Per year 60% part of total nitrogen fixing by biological nitrogen fixing on Earth Two types Symbiotic A part of biological relationship in which plants provides a niche and fixed carbon to bacteria in exchange for fixed nitrogen. Non symbiotic (Associative) A process of biological nitrogen fixation performed by a group of autotrophic bacteria living free in the soil either aerobically or anaerobically and not depend on plant. 16

17. Associative nitrogen fixation Symbiotic nitrogen fixation Non-symbiotic nitrogen fixation bacteria are free living in the soil. Symbiotic nitrogen fixation bacteria live in a mutualism relationship with plants. Ammonia , nitrites and nitrates are formed. Ammonia, Amino acids, and ureides are formed. Non-symbiotic bacteria make nitrogen available in the soil. Symbiotic bacteria produce nitrogen for its host. Ex : Azotobacter spp ., Beijerinkia , Gluconobacter , etc. Ex : Rhizobium meliloti , Rhizobium trifolii, Rhyzobium leguminosarum. Difference between associative & symbiotic N fixation (Important) 17

18. Associative Nitrogen Fixation [ANF] Associative nitrogen fixation, the process by which dinitrogen gas is converted to ammonia by bacteria in casual association with plants has not been well-studied in temperate ecosystem. Fixation carried out by free living micro-organisms. They inhabit both terrestrial & aquatic habitats. 18

19. Aerobic, anaerobic, and blue green algae. Bacteria : special type (nitrogen fixing bacteria) types, Free living aerobic : Azotobacter, Beijerenkia Free living anaerobic : Clostridium Free living photosynthesis : Cholorobium, Rhodopseudomonas Free living chemosynthetic : Desulfovibro, Thiobacillus Free living fungi : Yeast and Pillularia 19

20. Blue green algae; Unicellular- Gloethece, Synechococcus Filamentous;(non heterocystous)- Oscillatoria plectonema. Filamentous(heterocystous)- Anabeana, Nostoc 20

21. In ecosystems where legumes are sparse or absent, associative nitrogen fixation or nitrogen fixation by free living diazotrophic bacteria associated with the roots of non-leguminous plants, can be a mechanism for meeting part of the N requirements of plants. Associative N fixation has been reported in both C 3 and C 4 grasses but C 4 grasses may be better candidates for associative N fixation because of their greater photosynthetic efficiency. Associative N fixation appears to be more common in tropical and subtropical environments, but low rates of associative N fixation have been reported for several C 4 species including corn, sorghum and switch grass. 21 Importance of associative nitrogen fixation

22. It has been recognized for a long time that associative N 2 -fixing biological systems in wetlands enrich the soil organic N pool and supply up to 113 kg N/ha to rice crop depending upon the ecosystem, cultural practices and rice variety grown. Inhibitory effect of exogenous supply of N fertilizer indicates limited potential of associative N 2 fixation to significantly benefit agriculture. Farmers would have to withhold N fertilizer from their rice crop in order to increase biological N 2 -fixation associated with rice. 22

23. In addition, scare and the increasing cost of non-renewable chemical fertilizers necessitates the greater use of renewable indigenous biological N 2 -fixation system as source of N for the rice. Part of fixed N is available to the plant immediately Plant associated N 2 fixation is less sensitive to N fertilizer application These associations are of great importance as a substitute for nitrogen fertilizer. 23

24. Factors affecting N 2 fixation Presence of nitrate or ammonium. Presence of certain inorganic substances Ca, Co, Mo- influence N 2 fixation along with P PH : Neutral – Azotobacter Acidic – Beijerinkia Soil moisture : adequate is good for fixation Temperature : mesophilic-30 C. 24

25. Summary In associative nitrogen fixation mainly involved free living microorganisms as aerobically or anaerobically and not depend on plant. Here associative nitrogen fixation microorganisms are introduced to grasses family plants economically significant. Thereby nitrogen requirement will be depended on associative microorganisms. Both free living bacteria, fungi and algae are involved with this associative nitrogen fixation. 25

26. However this nitrogen fixation very depend on C4 or C3 variation. In C4 plant having high level of nitrogen fixation but C3 having low level of nitrogen fixation that C3 nitrogen fixation level can increase using new technology such as converting C3 to C4 plant, using recombination DNA technology. However that ANF is very applicable to rice plantation other than symbiotic nitrogen fixation because of ANF bacteria do not require special host plant. Simply, Here mechanism is free living microorganisms are absorbed of atmospheric nitrogen to form protoplasm, that fixed nitrogen are available for plants after the decomposing those microorganisms. 26

27. References Agrawal. K and Sharma. J (2008), Plant physiology & Biochemistry, 1 St edition, CBH application, Jaipur. Singh V, Panday PC, Jain DK. (2009-2010), Plant physiology & Biochemistry, 3 rd edition, Rastogi publication, Meerut, New Delhi. J. Range Manage. 471192-196, May 1994. Indications of associative nitrogen fixation in eastern Gamagrass. Panday, S N and Sinha, BK. (1994), Plant physiology, 2 nd edition, Vikas publication house, New Delhi. 27

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