Energy, ecosystems, nutrient cycles, succession

• Biomass is all the biological molecules made by the plant and are not immediately used for respiration.
• Biomass is measured as:

  • mass of carbon
  • dry mass (KgM-2yr-1)
  • An energy value (KjM-2yr-1)
• Practical estimation of dry mass:

  1. heat in low temperature oven to evaporate water In the tissues
  2. until there is no further change in mass
  3. calculate dry mass in KgM-2y-1
  4. carbon content estimated as 50% of dry mass
• Energy in dry biomass:

  1. dried biomass from a known area placed in a calorimeter
  2. the dry biomass is then burnt
  3. the energy released is used to heat water
  4. the change in water temperature is used to calculate the energy released
  5. energy per square metre per year is calculated (KjM-2yr-1)
• Gross primary production: total amount of light energy captured in photosynthesis and stored in molecules as chemical potential energy
• Respiration: the amount of energy lost from the plant in respiration this returns to the envronment as waste heat
• net primary production: this is the remaining amount of chemical potential energy stored in the biomass of the plant. this can be used for growth and reproduction
• NPP = GPP - R
• Only about 1 - 5 % of the light energy falling on a leaf is captured in photosynthesis, this is for several reasons:

  • some light is reflected from leaf’s surface
  • only certain wavelengths of light absorbed by chlorophyll
  • light may not hit chloroplast
• Net production in consumers:

  • consumers get their energy by ingesting biomass
  • some used for respiration by the consumer and is lost eventually as heat
  • some lost as faeces and urine
  • the rest is used for growth
• Net production (N) = chemical energy in ingested food (I) - ( energy lost as faeces and urine (F) + respiratory losses (R) )
• A trophic level is the feeding position of an organism in a food web
• %Efficiency of Energy Transfer

  Net production of trophic level / Net production of previous trophic level x 100
• Reducing energy losses by animals:

  • reduce movement so less energy used in movement and more is used in net production
  • keep in heated habitats so less food used to keep itself warm
  • kill the animal once it has completed its growth
  • concentrated feeds that are easily digested and absorbed
• Simplifying food webs:

  • pesticides - remove insect and other animal pests that eat the crops
  • herbicides - kill weeds which are competitors of the crop plant so reduce yields
• Processes of nutrient recycling

  • Uptake
  • Feeding
  • Decomposition
• Saprobionts are bacteria which secrete digestive enzymes which decompose dead material
• Mycorrhizae are fungi that live in close association with plant roots. They provide a large surface area for uptake of minerals from soil. In return, the plant provides carbohydrates