Resource capture by localized root proliferation: Why do plants bother?

Using data from a well-known, published experiment [Drew (1975) The new Phytologist 75: 479-490], the potential exploitation of locally available nutrients by barley roots is calculated. Local proliferation of lateral roots does not necessarily achieve significantly greater exploitation of mobile soil resources like nitrate, but it does for less mobile ones such as phosphate. Despite this, the magnitude of the proliferative response is as great to locally available nitrate as it is to phosphate. This implies an 'over-production' of roots in response to localized nitrate availability, prompting a re-evaluation of the nature and implications of the response mechanism(s) of roots to soil heterogeneity. (C) 1996 Annals of Botany Company