nutrient cycling

4 stages of the nitrogen cycle

nitrogen fixation

ammonification

nitrification

denitrification

nitrogen fixation

carried out by nitrogen fixing bacteria

N₂ → NH₃/NH_4⁺

catalysed by nitrogenase and ATP

where does the N₂ in nitrogen fixation come from

the air

what’s special about nitrogen fixing bacteria

it has a mutualistic relationship with legumes

ammonification

carried out by saprobionts

organic N → NH₃/NH₄⁺

where can you find organic nitrogen

amino acids

DNA

urea

nitrification

carried out by nitrifying bacteria

NH₃/NH₄ → NO₂^- → NO₃^-

use of NO₃^-

absorbed by plants and assimilated into plant proteins

denitrification

carried out by denitrifying bacteria

NO₃^- → N₂

conditions for denitrification

anaerobic conditions

waterlogged soil

where can phosphate ions be released from

sedimentary rocks (weathering)

bone decay

shells

excretion of birds

what is mycorrhizae

fungi with a mutualistic relationship with plants

what is a mutualistic relationship

beneficial to both organisms

role of mycorrhizae

facilitates the uptake of water and organic ions by plants

how do mycorrhizae help plants

increase the surface area

act as a sponge holding water and minerals

what are the benefits to the plant of mycorrhizae

better drought resistance

easier to take up inorganic ions

what is the benefit to the mycorrhizae

glucose

what are fertilizers used for

replace the nitrates and phosphates lost from the soil through harvesting plants and removing livestock

benefits of artificial fertilizer

easy to handle and store

there’s a known concentration of nutrients bene

benefits of organic fertilizer

improvement of soil condition because of organic content

wide range of nutrients

slow release of ions with less risk of leaching

negative impacts of fertilizer

reduced biodiversity

leaching

eutrophication

what is leaching

when mineral ions dissolve in rainwater and wash into rivers and lakes

what is eutrophication

an increase in the nutrient concentration in bodies of water

how can this lead to the death of an ecosystem

growth of algal bloom blocks sunlight

photosynthesis stops occurring in submerged plants and they die

saprobionts decompose the plants by respiring aerobically

oxygen concentrations drop , killing animals

what is left in the water after ecosystem death

high number of low O₂ tolerators e.g tubifex worm