• In natural ecosystems,?nutrients?(such as nitrogen and phosphorus) are?recycled?through food webs
• For example, these nutrients get passed on from?producers?to?primary consumers?when they feed on the producers and from?primary consumers?to?secondary consumes?when they feed on primary consumers
• Microorganisms?are very important in ensuring that the nutrients that are stored within?dead organisms?and in the?waste products?of organisms (i.e. faeces and urine) are?recycled?and made?available?to?producers?once again
  • This process is known as?decomposition

   

Saprobionts

• True decomposers are known as?saprobionts
• Saprobionts are mainly made up of?fungi?and?bacteria
• Saprobionts?secrete enzymes?onto their food (dead organisms and waste material), which then digest the material externally
  • This process is also known as?extracellular digestion
  • The?products?of this external digestion are then?absorbed?by the saprobionts

   

• This method of obtaining nutrients from dead or waste organic matter via extracellular digestion is known as?saprobiotic nutrition
• Saprobionts secrete a wide range of digestive enzymes that allow them to hydrolyse (break down) a large variety of biological molecules, releasing a large range of products (nutrients) as a result
  • For example, mineral ions such as?ammonium?and?phosphate?ions?that are important for the growth and function of producers (e.g. plants) may be released as products during saprobiotic nutrition

   

• Importantly,?not all?of the products of extracellular digestion get absorbed by saprobionts and many?remain?in the surrounding environment (e.g. the?soil) and are available to be absorbed by?other organisms?(e.g. plants)
  • This is why saprobionts are such an essential component of ecosystems and food webs
  • Without them, the nutrients locked up in dead and waste matter would never be made available again and producers such as plants would not have access to sufficient nutrients
  • In addition, some saprobionts even?excrete?important?nutrient mineral ions?as?waste products?from their own metabolism

   

Mycorrhizae

• Many plants have evolved?symbiotic?(mutually beneficial) relationships with?fungi
  • The fungi are composed of long, thin filaments known as?hyphae, which?interact?with the?roots?of the plants
  • These hyphae?greatly increase?the?surface area?of the root systems of the plants, increasing the amount of?water?and?mineral ions?(e.g. nitrates and phosphates) that can be absorbed by the plants' roots
  • In return, the fungi receive?organic compounds?(e.g. glucose) from the plant

   

• These relationships between plant roots and fungi are known as?mycorrhizae

An example of a mycorrhiza (plural = mycorrhizae) - the mutual, symbiotic relationship between a fungus and the roots of a plant

Summary of the role of microorganisms in recycling minerals