Theories and causes

C3 and C4 grasses and starch

  • Grass species can be divided into two groups: C3 grasses that thrive especially in colder climates and seasons and C4 grasses that grow well in hot, humid climates and seasons.
  • This classification is based on the different ways photosynthesis takes place in these types of grass. C4 grasses need more light and warmth to transform atmospheric carbon dioxide into organic compounds and are therefore better adapted to warmer climates and seasons.
  • More differences are found in water requirements, frost sensitivity, nutritional value and yield of the grass.
  • Stems and leaves of C3 grasses contain hardly any starch. Only when C3 grass is in full bloom, the plant can contain up to 4% starch. The seeds of C3 grass plants do contain starch.
  • C4 grasses usually do contain starch. Starch is the way C4 grasses temporarily store excess sugar, the same way C3 grasses use fructan as a means of storage. However, starch content in C4 stems and leaves is low. Most starch in C4 grass can be found in the seeds, just like in C3 grass.
  • In Europe, pasture predominantly or entirely consists of C3 grasses such as timothy grass, brome grass and orchard grass. In America, Australia and New Zealand both C3 and C4 grasses grow, but also in these countries C3 grasses are the majority. Sometimes C4 grasses such as sorghum and sudan grass are added to existing pasture.
  • It is tempting to suggest that starch concentration in grass from these continents may be higher. However, differences in starch concentrations largely depend on the amount of seed a grass sample contains.