ABSTRACT
Carbon and nitrogen are two of the dominant nutrients regulating plant growth. They are integral components in virtually all essential metabolic functions. Where should a discussion of carbon and nitrogen interactions begin? Perhaps the most appropriate conceptual framework comes from ‘Interdependence Theory’. Through the work of a number of research groups, it is known that shoot and root growth are co-ordinated (Brouwer, 1962; Brouwer and De Wit, 1969; Ingestad, 1979; Ingestad and Lund, 1979; Raper et al., 1978). For a given growth environment and developmental stage, there will be a characteristic shoot and root dry matter distribution ratio. If the shoot and root dry matter ratio is disrupted, for example by excision of a major portion of either plant part, then disproportionate regrowth occurs until the characteristic shoot and root distribution pattern is reestablished. Further, if the growth environment is altered, such as by altering nutrient availability, the shoot to root growth ratio (S/R) adjusts to a new characteristic set point.
