Growth in Scots pine (Pinus silvestris L.) : Mechanism of response to nitrogen.

A theory of mechanisms underlying growth response to nitrogen in Scots pine is developed. Nitrogen in needles is considered as distributed in two mutually exclusive pools, viz. mobile and structurally bound. The size of the former pool, relative to total needle biomass, determines the rate of production of new needle biomass; this process decreases the pool size due to immobilization of mobile nitrogen. Some implications of the theory are derived and compared with published experimental results. It predicts a one-year time delay between a pulse fertilization and commencement of growth response, the latter having a total duration of about ten years with a maximum after about three; these predictions are not contradicted by available data.