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Recap... Recap... Recap... ● Angiosperms – – ● ~82% Dicots ~79% Monocots Gymnosperms – 100% Recap... ● Andropogon gerardii ● ~92% of P – 75+17 http://upload.wikimedia.org/wikipedia/commons/4/4f/Andropogon_gerardii_(3904160434).jpg Recap... Cost of having mycorrhizae is about ~80% of the C Nitrogen in the Ecosystems ● ● ● ● Most limiting nutrient in many terrestrial ecosystems Rapid turnover rate and can be lost rapidly to the atmosphere Nitrogen in the form of Dinitrogen (N2) makes up 80% of the air we breathe but is essentially inert due to the triple bond A constant reduction of Dinitrogen gas (N 2) to Ammonia is required Law of the Minimum http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec122sts/liebigbarrel.gif Nitrogen Fixation • The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy. Three processes are responsible for most of the nitrogen fixation in the biosphere: atmospheric fixation biological fixation industrial fixation The Nitrogen Cycle http://teagueesorientation.wikispaces.com/file/view/nitrogen_fixation.jpg/237226552/nitrogen_fixation.jpg Biological Nitrogen Fixation ● Symbiotic N Fixation – Leguminous – Actinorhizal – Specialized Loose Relationships – ● Free Living N Fixation – Biological Soil Crust – Lichens Biological Nitrogen Fixation Biological Nitrogen Fixation A sensitive process ● ● ● The biological reduction of dinitrogen can only be carried out by some prokaryotes The process is highly sensitive to Oxygen Symbiotic relationships are established so that the plant provides energy (carbon) and the anoxic environment http://www.escience.ws/b572/L20/images/wnod29.jpg Leguminous Plants ● ● Association between plants of the Fabaceae familly ( beans) and bacteria of the genera: – Rhizobium – Bradyrhizobium – Sinorhizobium – Mesorhizobium – Azorhizobium Nodules are formed in the roots Nodule Formation http://images.tutorvista.com/content/plant-nutrition/root-nodules-formation.jpeg Actinorrhizal Associations ● Associations between nonlegume plants and bacteria of the genus Frankia – Alnus (alder) – Hippophae – Myrica Elaeagnus' – – – Dryas Casuarina Specialized Associations ● Association Between cyanobacteria (Nostoc and Anabaena) and plant species – No nodules are formed – The cyanobacteria does not fix CO2 Loose Associations ● Bacteria living in the rhizosphere that can associate with specific plant species – Azospirillum & Tropical Grasses – Acetobacter & Sugar Cane Loose Associations ● Bacteria living in the rhizosphere that can associate with specific plant species Loose Associations ● Bacteria living in the rhizosphere that can associate with specific plant species Loose Associations ● Bacteria living in the rhizosphere that can associate with specific plant species Free Living Nitrogen Fixation ● Soil Biological Crust: Complex community of cyanobacteria, mosses, and lichens Free Living Nitrogen Fixation ● ● ● Lichens: Simbiotic association between a fungi and algae or a cyanobacteria "Lichens are fungi that have discovered agriculture"-- Trevor Goward. The cyanobacteria remains photosynthetically active Carbon and Energy Metabolism of the Nodules ● ● The plant provides Carbohydrates via the phloem. Carbohydrates are broken down to Malate and Succinate Nitrogenase Reaction Nitrogen Fixation ● ● Nitrogenase: Enzyme that catalizes the reduction of dinitrogen to ammonia Two Proteins: – Fe-S: Accepts electrons from NADPH and binds ATP – Fe-Mo: Binds N2 Carbon Cost of the Legume-Rhizobium Association ● ● ● Maintaining the association is not free Rhizobium requires organic acids for N2 Fixation and Carbon for nodule maintenance The cost of the association is higher than assimilating N if it was available for the plant Carbon Cost of the Legume-Rhizobium Association ● ● The cost for N2 fixation is ~25% of the daily C fixed by photosynthesis 12g C 1g Fixed N Factors that affect N Fixation ● Circles=No Fertilizer ● Triangles= Fertilizer ● Solid=83 ● Open=84 Factors that affect N Fixation Factors that affect N Fixation ● Water availability ● P Availability ● Compatibility between plant and bacteria – Associations can be highly specific Factors that affect N Fixation ● Water availability ● P Availability ● Compatibility between plant and bacteria – Associations can be highly specific Nitrogen in the Global Scale Nitrogen in the Global Scale Physical Nitrogen in the Global Scale Retranslocation within Plants Nitrogen in the Global Scale Physical Nitrogen Fixation Industrial N Fixation http://people.idsia.ch/~juergen/worldpopgrowth4.jpg
