- A change in a habitat causing a change in the make-up of a community.
Succession on Sand Dunes
- Pioneer plants like sea rocket (Cakilemaritima) and prickly sandwort (Salsola kali) colonise the sand just above the high water mark - tolerate salt water, lack of freshwater and unstable sand.
- Wind-blown sand builds up around the base of these plants, forming a 'mini' sand dune.
- As plants die and decay, nutrients accumulate in this mini sand dune.
- As the dune gets bigger, plants like sea sandwort (Honkenyapeploides) and sea couch grass (Agropyronjunceiforme) colonise it, which have long roots to stabilise it in the sand.
- With more stability and accumulation of more nutrients, plants like sea spurge (Euphorbaparalias) and marram grass (Ammophilaarenaria) start to grow.
- Marram grass traps sand, as the sand accumulates, the shoots grow taller to stay above the growing dune trapping more sand.
- As the sand dune and nutrients build up, other plants colonise the sand, such as hare's foot clover (Trifoliumarvense) and bird's foottrefoil (Lotuscorniculatus).
- These have bacteria in their root nodules to convert nitrogen into nitrates.
- With nitrates available, more species like sand fescue (Festucarubra) and viper'sbugloss (Echiumvulgare) colonise the dunes, stabilising the dunes further.
Role of Decomposers
Decomposers, such as bacteria and fungi, break down dead and waste organic material.
Bacteria and fungi feed saprotrophically so are called saprophytes.
They secrete enzymes onto dead and waste material.
The enzymes digest the material into small molecules, which are then absorbed into the organisms body.
Having been absorbed, the molecules are stored or respired to release energy.
If bacteria and fungi did not break down dead organisms then energy and valuable nutrients would remain trapped in the dead organisms.
Microbes get a supply of energy to stay alive, and the trapped nutrients are recycled.
- Nitrogen gas is very unreactive, so is impossible for plants to use it directly.
- Nitrogen is needed to make proteins and nucleic acids.
- Plants need fixed nitrogen as ammonium ions (NH4+) or nitrate ions (NO3).
- Bacteria is involved in the recycling of nitrogen.
- Nitrogen fixation can occur when lightning strikes or through the Haber process - only 10% of total nitrogen fixation.
- Nitrogen-fixing bacteria live freely in the soil and fix nitrogen using it to make amino acids.
- Nitrogen-fixing bacteria, such as Rhizobium, also live inside the root nodules of legumes (bean plants).
- They have a mutualistic relationship with the plant, fixing nitrogen and receiving carbon compounds such as glucose in return.
- Proteins, such as leghaemoglobin, in the nodules absorb oxygen to keep the conditions anaerobic.
- Under these conditions, the bacteria use nitrogen reductase to reduce nitrogen gas to ammonium ions (NH4+) that can then be used by the host plant.
- Nitrification happens when chemoautotrophic bacteria in the soil absorb ammonium ions.
- Ammonium ions (NH4+) are released by bacteria involved in putrefaction of proteins found in dead or waste organic matter.
- Chemoautotrophic bacteria obtains energy by oxidising ammonium ions (NH4+) to nitrites (NO2-) (Nitrosomonas bacteria), or by oxidising nitrites (NO2-) to nitrates (NO3-) (Nitrobacter bacteria).
- As oxidation requires oxygen, these reactions only happen in well-aerated soils.
- Plants need nitrates to make amino acids, proteins, enzymes, DNA, RNA, etc.
- Other bacteria convert nitrates back to nitrogen gas.
- When the bacteria grows under anaerobic conditions, such as waterlogged soils, they use nitrates (NO3-) as a source of oxygen for their respiration and produce nitrogen gas (N2) and nitrous oxide (N2O).
That's the end of the topic!
Drafted by Bonnie (Biology)