Essential idea: Soil cycles are subject to disruption. By Chris Paine https ://bioknowledgy.weebly.com/ Intensive agriculture relies heavily on the use of artificial fertilisers to maintain high crop yields. The manufacture and the application of fertilisers is a major disruption to nutrient cycles. One consequences of this is the unbalancing of natural ecosystems around agricultural areas. C.6 The nitrogen and phosphorus cycles (AHL)
22
Embed
BioKnowledgy C.6 The nitrogen and phosphorus cycles (AHL)
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Essential idea: Soil cycles are subject to disruption.
By Chris Paine
https://bioknowledgy.weebly.com/
Intensive agriculture relies heavily on the use of artificial fertilisers to maintain high crop yields. The manufacture and the application of fertilisers is a major disruption to nutrient cycles. One consequences of this is the unbalancing of natural ecosystems around agricultural areas.
Azotobacter are free-living in the soil whereas bacteria of the genus Rhizobiumare often not free-living but live in a close symbiotic association in the roots of plants such as the legume family.
Mutualism describes relationships between organisms in which both organisms benefit.
Legumes and the Rhizobium grow together to form nodules on the roots of the legume.
The legume supplies carbohydratesto the bacteria. The bacteria use the carbohydrates for processes such as respiration.
The bacteria supply ammonia (fixed from atmospheric nitrogen) to the legume.
The legume requires ammonia for the synthesis of amino acids.
C.6.A1 The impact of waterlogging on the nitrogen cycle.
n.b. excess water in the soil also leads to greater leaching of nutrients, which leads to nutrient enrichment of rivers and lakes and therefore to eutrophication.
C.6.A2 Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils.
http://botany.org/Carnivorous_Plants/
Dionaea muscipula - The Venus Flytrap
Drosera sp. - the Sundews
“Carnivorous plants have the most bizarre adaptations to low-nutrient environments. These plants obtain some nutrients by trapping and digesting various invertebrates, and occasionally even small frogs and mammals. Because insects are one of the most common prey items for most carnivorous plants, they are sometimes called insectivorous plants. It is not surprising that the most common habitat for these plants is in bogs and fens, where nutrient concentrations are low but water and sunshine seasonally abundant.”
On this diagram the pools (boxes) and fluxes (arrows) have been drawn on already. Add in the processes and state the bacteria related to the some of the processes.
Rhizobium
free-living nitrogen-fixing bacteria in the soil
Azotobacter
Mutualistic nitrogen-fixing bacteria in root nodules
Nitrification (x2) Nitrosomonas
Nitrobacter
Uptake (by active transport) and assimilation by plants
Natural nitrogen fixation by lightning
Application of fertiliserscontaining nitrogen (fixed by the Haber process)
Organisms have a variety of uses for phosphate• ATP• DNA and RNA• cell membranes• skeletons in vertebrates
The rate of turnover (the speed of movement of phosphorous from one pool/sink to another) is relatively slow, compared with Nitrogen, as phosphate is only slowly released to ecosystems by weathering.
Certain rocks, e.g. Phosphorite, contains high levels of phosphate minerals. Weathering of these rocks releases phosphates into the soil. Phosphates are a form of phosphorus that can is easily be absorbed by plants and hence enter food chains.
The phosphorous cycle shows the various different forms in which
The graph is based on US Geological Survey data and shows world phosphate production from mining.
World production has varied greatly, but overall there have been smaller increases toproduction after than before 1980.
As the reserves of phosphate rock are depleted the production of phosphorous is likely to peak and then decline. Though some sources the peak is likely to occur in in the next 30 years it is difficult to judge particularly due to the fact new phosphate mineral deposits are still being discovered.
C.6.U7 Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and
leads to increased biochemical oxygen demand.
The consequences to organisms of low levels of dissolved oxygen:• death or emigration of oxygen sensitive organisms (e.g. fish)• proliferation of low dissolved O2 tolerant organisms• reduction of biodiversity• decrease in water transparency, i.e. an increase in turbidity stresses
photosynthetic organisms …• … this in turn will affect the whole food chain• increased levels of toxins and greater numbers of pathogens means
affected water is no longer suitable for bathing or drinking
An increase in nutrients in aquatic ecosystems leads to eutrophication.
C.6.S2 Assess the nutrient content of a soil sample.
Guidance on proper use of tests and limitations of simple home test kits: http://www.ext.colostate.edu/mg/gardennotes/221.html#kits
Garden supply companies commonly sell soil quality assessment kits. The kits involve adding a chemical to a sample of soil that reacts with the nutrient in question, if present. A colour is produced that can be visually compared to a key.
An example kit from Urban Farmer: http://www.ufseeds.com/Premium-Soil-Test-Kit.item