Gross Primary Production
- During photosynthesis, primary producers (such as plants and algae) convert light energy to chemical energy stored within biological molecules
- Gross primary production (GPP) can be defined as the amount of chemical energy stored in the carbohydrates within plants (during photosynthesis)
- Roughly only 1% of the light falling on a plant is used in photosynthesis to produce glucose
- 99% of the light either passes through the leaf without hitting chloroplasts, is reflected off of the leaf, or is transferred to heat energy
- After that 1% is successfully absorbed and used to form glucose, the quantity of energy now stored in glucose is the gross primary production
- Gross primary production can be expressed in:
- Units of energy per unit area, for example
- J m–2 (joules per square metre)
- kJ km-2 (kilojoules per square kilometre)
- In this case, ‘area’ refers to the area of land that is being studied (this land contains the primary producer(s) that are producing the biomass - if there are no primary producers present in this area of land, there will be no gross primary production)
- Units of mass per unit area, for example
- g m–2 (grams per square metre)
- kg km-2 (kilograms per square kilometre)
- Units of energy per unit area, for example
- In aquatic environments, it may be more suitable to measure gross primary production per unit volume
- For example, for aquatic algae, gross primary production could be given in:
- kg m-3 (kilograms per cubic metre)
- kJ m-3 (kilojoules per cubic metre)
Gross primary productivity
- The rate at which plants are able to store chemical energy via photosynthesis is referred to as gross primary productivity
- Gross primary productivity is expressed using units of energy/mass per unit area per unit time
- Time must be included as it is a rate
- For example
- Mj m–2 y-1 (megajoules per square metre per year)
- kg km-2y-1 (kilograms per square kilometre per year)