Environmental effects on dry matter partitioning between shoot and root of crop plants: relations with growth and shoot protein concentration

The literature on environmental effects on dry matter partitioning in higher plants, in particular crop plants, is reviewed focussing on changes in shoot to root dry weight ratio (S:R). Of particular consistency is the finding that S:R increases with increased nitrogen (N) supply. Relations between nitrogen (N) supply, growth, S:R and tissue N and protein concentration are examined. In some cases, the increase in S:R with increased N supply is likely to have been at least in part an effect on growth and development, but there is unequivocal evidence that N affects S:R independently of growth and development. A positive correlation between S:R and leaf protein concentration is highlighted. It is argued that the N effect on S:R outside the effect on growth and development is related to increased shoot protein concentration. Specifically, shoot and root growth are colimited by local carbon (C) and N (primarily protein) substrate concentrations and shoot growth will increase relative to root growth with increased N substrate availability due to the proximity of the shoot to the C source. It is further argued that results in the literature are consistent with the proposal that macronutrient, water, irradiance, CO₂ and temperature effects on S:R are often primarily mediated through their effects on growth and development, and shoot protein concentration and hence shoot growth.