Biogeochemical Cycles Flashcards
What nutrients are microbially transformed?
-Carbon - fixing, decomposition
-Nitrogen
-Sulphur
-Phsophorus
-Iron (micronutrient)
Whta chemical transformations can bacteria perform?
-degradation of organic matter
-disease suppression
-disease causation
-nutrient transformations inside roots
-bacteria are main organisms in soil responsible for transforming inorganic constituents from one chemical to another
What do decomposers do?
-saprophytic fungi
-convert dead organic material into fungal biomass, carbon dioxide, and small molecules like organic acids
What do mutalists do and what are examples?
-The mycorrhizal fungi - colonise plant roots
-Ectomycorrhizae
-Endomycorrhizae
What do algae do?
Predominantly aquatic, but do occur in soils and have role in biogeochemical cycles
What does microalgae do?
Convert solar energy, CO2 and other nutrients into sugars, proteins and other complex organic compounds beneficial to the nutrient cycling and soil structure
-some species are able to fix atmospheric nitrogen- others form compounds conductive to the growth of associated plants
What is present in flooded paddy soils?
Blue-green algae Anabaena, Nostoc - fix N2, photosynthesis, argonomic importance (biofertiliser)
What are lichens?
Fungus and algae
What is Anabaena?
A genus of cyanobacteria
-these bacteria grow as chains of cells capable of photosynthesis with heterocysts where nitrogen is fixed
Nitrogen Cycle
Nitrogen in atmosphere - nitrogen-fixing bacteria in root nodules of legumes -ammonification - ammonium - nitrification- nitrifying bacteria - nitrites (NO2-)- nitrifying bacteria - nitrates (NO3-) - denitrifying bacteria - denifrification - nitrogen
What is the sulfur content of soil composed of?
Sulphonates and sulphate esters (more than 95%) with inorganic sulphate constituting less than 5% of sulphur content
What do crops need sulphur for?
Crops rely upon uptake of inorganic sulphur as a nutrient for the synthesis of cysteine and methionine (amino acids for proteins) and a number of essential vitamins and cofactors.
Why are sulphonates and sulphate esters not directly plant available?
-Sulphonates and sulphate esters consist of sulphate bound to organic molecules and are consequently not diectly plant available
-Rhizobacteria including Pseudomonas species can enzymatically hydrolyze sulphonates and sulphate esters to release inorganic sulphur as sulphate to make it available to the plant
Sulphate deficiency in wheat?
Leads to growth impairment and chlorosis
In some areas sulphur deficiency is averted by acid rain
Look at phosphate cycle
What affect phosphate levels?
-Although phosphate may be applied to soil as fertiliser to supplement plant nutrition, biological immobilisation and chemical precipitation can deplete the available phoisphate stores
-Phsophate-solubilising bacteria (PSB) may play an important role in supplying phosphate to plants
How does phosphate-solubilising bacteria work?
PSB have the ability to solubilise unavailable forms of calcium-bound Phosphate by excreting organic acids which chelate calcium ions to bring phosphate into solution
The production of these organic acids result in a decrease in soil pH which aids solubilisation
What are the most frequently secreted organic acid used in bacterial phosphate solubilisation?
Gluconic acid - most
2-ketogluconic acid
What bacteria secretes gluconic acid?
Pseudomonas species
Erwinia herbicola
Burkholderia cepacia
What strains secrete 2-ketogluconic acid?
Rhizobium leguminosarum
Rhizobium meliloti
Bacillus firmus
What is iron present in?
4th most abundant element in earth crust
-present in 2 oxidation states
–Fe3+ is very insoluble
–Fe2+ is more soluble
What is iron rewuired for?
-Enzyme cofactor e.g superoxide dismutase
-Haem of cytochromes
-Iron-molybdenum protein (Fe-Mo protein) in nitrogenase complex
-Iron protein (Fe protein) in nitrogenase complex
-Iron-sulphur complex in enzymes such s dinitrogen reductase aconitase
-Aromatic amino acid biosynthesis
Microbial Iron Assimilation/uptake?
-Secretion of siderphores which are (ferric) iron chelating compounds
-Uptake of ferric-siderphore compound via specific receptor mechanism
-Release and reduction of iron from ferric-siderphore within the cell
-Iron availability intracellularly as Fe2+ for multiple functions (enzyme cofactor, cytochrome structure etc)
-Switch off iron-uptake mechanism when cell has sufficient iron
LOOK at last slide diagram
