Plant nutrition, dry matter gain and partitioning at the whole-plant level

Differential flows of photoassimilate result in patterns of dry matter distribution among plant organs. The extent to which these patterns are dependent on the flux of different mineral nutrients entering the root and the extent to which the distribution of dry matter in the whole plant is affected by differentials in nutrient (primarily nitrate) flux among parts of the root system is considered. It is concluded that patterns of dry matter distribution and nutritional status may depend on how nutrient supply has been manipulated about the root. Where the flux density of nutrient has been decreased and has become limiting to plant growth, two categories of response have been observed. In the case of N, P or S, limiting flux density results in a proportionately greater amount of plant dry matter in roots than is found at higher flux densities. This contrasts with the case of limiting K, Mg or Mn supply, where proportionately less plant dry matter is found in roots at lower nutrient flux densities than at higher flux densities. In the case of N, particular attention is paid as to how sink strength may be related to differences between root and leaf cells in their capacity for loosening and synthesis processes in the primary cell wall.