A vegetative plant growth model: adaptive significance of phenotypic plasticity in matter

A model of vegetative plant growth was constructed upon three assumptions derived from a sand-culture experiment with Polygonum cuspidatum Sieb. et Zucc.: (1) the partitioning of dry matter and nitrogen between organs is controlled by the nitrogen concentration of the whole plant; (2) specific leaf weight (SLW) is controlled by leaf nitrogen concentration; and (3) net assimilation rate is a function of nitrogen concentration per unit leaf area. Model simulations gave the relative growth rates under steady-state exponential growth for different nitrogen uptake rates per unit root weight. The significance of phenotypic plasticity in matter partitioning and SLW is discussed, comparing the growth of plants which modify their partitioning and SLW with those less plastic in these respects. Plants with plasticity in both matter partitioning and SLW always attained the higher growth rate under varying availabilities of nitrogen in the environment. Plasticity also contributed to the efficient use of nitrogen in plant growth.