Phosphorous Flashcards
Why is p important
essential nutrient for plants and animals in the form of ions
PO4^3-
HPO4^3-
It is part of DNA molecules, ATP and ADP, and of fats of cell membranes. Also key building block for parts of animals like bones and teeth
Why is it limiting for plant growth
bc conc of p accessible in soil (free orthophosphate ions- PO4^3-) is quite low. Availability of P limited by rate of release of P during weathering
P itself is not scarce but exists predominantly in insoluble forms eg apatite. The soluble p mobilised by weathering is rapidly immobilised by iron and aluminium and sometimes Ca in soil
Talk about fertiliser
NPK fertiliser very population
2:1:1 ratio
People had thought dominant form of nutrient limitation was N, now questioning
Talk about p cycle
P cycle doesn’t have gaseous phase. Can be phosphorous/phophate or organic form in living material
It is recalcitrant - resistant to chemical deposition
Freeze thaw can break up dead connective tissues by damaging cells. When this happens get a flush of p in spring when soil warms. Dead things like leaves all decomposed and release DNA. Phosphates cleave them. So P scarce just hard to get hold of.
POP
Nutrient limitation
Is driving force in ecosystem development. Current techniques to determine the nature of nutrient limitation use laborious field experiments.
Someone Hypothesised that the N:P ratio of the vegetation is directly indicative of the nature of nutrient limitation on a community.
tested by reviewing data on fertiliser studies in a variety of Eu freshwater wetland systems (bogs, fens etc)
Review of 40 revealed that:
an N:P ratio of >16 indicates P limitation
an N:P ratio of <14 indicates N limitation
Between 14 and 16 could be either or both
Measuring NP ratios is a simple and cheaper alternative to fert studies. Method can only be used under conditions where either NP controls for plant growth
Aquatic systems
In Many regions water scarcity and pollution are an issue
Including the mobilisation of bioavailable nutrients eg NP in watershed. Significant amounts enter water and are transported to rivers and seas. Human activities have altered NP cycles -> eutrophication.
Two of the most commonly recognised symptoms of eutrop are harmful algal blooms and hypoxia
In water p is not easily immobilised bc Fe, Al, and Ca cons much lower in water –> eutrophication. P mostly as phosphate ions from industrial waste, sewage and detergents- often directly discharged into h2o where it is quickly utilised by plants and phytoplankton.
If p input is large enough, n becomes limiting. but only for a short period, blue-green algae and other n-fixing organisms then start their activity thereby bringing system into balance with elevated p - accelerates plant and plankton growth
nutrient loading in many rivers have increase the hypoxic zones in Eu and N. USA attributed to fertiliser
In S. america, africa, and asia animal manure and sewage often an important anthropogenic cause. Algal blooms can be toxic.
Bioavailable N and P numbers due to humans
Bioavailable N has nearly doubled
Bioavailable P has nearly tripled
Washing up liquids
Have high P
They get into grey water (drainage) that meets sewage’ that gets processed. Bacteria can’t reduce it all. Often P limiting in aquatic systems. –> algal bloom
What are the most common anthropogenic sources of nutrients delivered to fresh water that end up in coastal systems?
agricultre, sewage, urban run off, industrial wastewater, and fossil fuel combustion
