C.6 The nitrogen and phosphorous cycle Applications: The impact of waterlogging on the nitrogen cycle Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils Understanding: Nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia Rhizobium associates with roots in a mutualistic relationship In the absence of oxygen denitrifying bacteria reduce nitrate in the soil Phosphorous can be added to the phosphorous cycle by application of fertilizer or removed by the harvesting of agricultural crops The rate of turnover in the phosphorous cycle is much lower than the nitrogen cycle Availability of phosphate may become limiting to agriculture in the future Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased biochemical oxygen demand Skills: Drawing and labeling a diagram of the nitrogen cycle Assess the nutrient content of a soil sample Nature of science: Assessing risks and benefits of scientific research: agricultural practices can disrupt the phosphorous cycle

Nitrogen Fixation 78% of atmosphere is nitrogen gas: N2 Plants cannot take up this form of nitrogen Bacteria ‘fix’ nitrogen gas and turn it into ammonia NH3 Plants can absorb this form.

Rhizobium Convert atmospheric nitrogen into a usable organic form. Live in close symbiotic association in the roots of plants Example of a mutualistic relationship

Rhizobium Create root nodules Convert atmospheric nitrogen in the soil into ammonia. Host plant cannot do this itself Plant provides the bacteria with carbohydrates produced during photosynthesis for energy

Ammonia  nitrites Ammonia produced by nitrogen fixation is converted to nitrite NO2 By bacteria: Nitrosomonas Use electrons gained from oxidation of ammonia to produce energy (chemoautotrophs)

Nitrites  nitrates Nitrites are then converted to nitrates By bacteria Nitrobacter Also chemoautotrophs as they gain energy from inorganic compounds Nitrate is a form that is available to plants

Water logging Soil saturated with water through flooding or irrigation with poor drainage Short supply of oxygen Favours denitrification Leads to Eutrophication Loss of nitrogen available to plants

Denitrification Denitrification is the reduction of nitrate NO-3 to nitrogen N2 By bacteria Pseudomonas denitrificans Use oxygen as an electron acceptor usually, however in oxygen short environments they use nitrates This releases N2 back into the atmosphere Reduces nitrogen available for plants

Nitrogen cycle Draw your own, including the following: Pools Fluxes/processes Nitrogen gas in atmosphere Nitrates Nitrites Ammonia Plant protein Animal protein Nitrogen fixation by living organisms Mutualistic nitrogen fixing bacteria in root nodules Free living nitrogen fixing bacteria in soil Nitrification by Nitrosomonas Nitrification by Nitrobacter Uptake and assimilation by plants Nitrogen fixation by non-living processes Transfer of nitrogen in the food chain death and decomposition Ammonification by decomposers Denitrification

Carnivorous plants Permanently water logged soils (bogs or swamps) Nitrogen deficient soils Become carnivorous to obtain nitrogen through digestion of animals

Phosphorous cycle Draw your own, include the following: Phosphate in soil Weathering Phosphate rocks Mining Geologic uplift Plant and animal waste Decomposers Run off and leaching Dissolved in waterways Shallow ocean sediments Deep ocean sediments

Phosphorous cycle Rate of turnover much lower than nitrogen cycle All living things require phosphorous to produce molecules: DNA, RNA, ATP Also for maintaining skeletons and cell membranes

Phosphorous cycle Phosphorite is a sedimentary rock containing high levels of phosphate-bearing minerals Weathering and erosion = release of phosphates into soil Phosphates readily taken up by plants = enters food chains

Human activity Affects phosphorous cycle. Phosphates mined and converted to phosphate based fertilisers Fertilisers transported elsewhere and applied to crops. Crops then harvested and transported elsewhere, taking phosphorous with it each time

Human activity Mining of phosphates is increasing due to intensive farming and demand for fertilisers Peak phosphorous = point in time at which the maximum global phosphate production rate is reached and then begins to fall due to depletion of reserves

Human activity No phosphate to mine = no fertilisers created No fertilisers = yields plummet No alternative sources of phosphates and no synthetic way to create it Global famine

Eutrophication Create a summary using the video: https://www.youtube.com/watch?v=6LAT1gLMPu4

Solutions to disruptions in phosphorous cycle Agriculture = removal of nutrients from an area Nutrients have to be re added using fertilisers Intensive farming = higher inputs needed to supply a growing population Searching for a solution for depleting phosphorous

Solutions to disruptions in phosphorous cycle Recover phosphorous from sewage Humans excrete between 200 – 1000 grams of phosphorous annually in urine Use bacteria that selectively accumulate phosphorous – removed and used as fertilisers Chemical precipitation with iron chloride (more expensive)

Solutions to disruptions in phosphorous cycle Genetic modification – Enviropig Produces phytase in its saliva. Able to digest normally insoluble phytate in pig feed. More phosphate absorbed, less released in manure Benefits Harmful effects Less release of phosphorus to the environment in pig manure Less risk of phosphorus deficiency in growing pigs Less need to deplete world mineral phosphate reserves by use as a dietary supplement in pig feed Traces of phytase in pork might cause allergies in humans Phytase gene might transfer to wild species by cross breeding GM might cause suffering to pigs in some way

Soil quality testing kits Soil testing Soil quality testing kits Add a chemical to a sample of soil that reacts with the nutrient in question if present Colour produced that can be visually compared to a key

Soil testing Leaf quality