GROWTH AND SHOOT - ROOT RATIO OF SEEDLINGS IN RELATION TO NUTRIENT AVAILABILITY

The influence of mineral nutrient availability, light intensity and CO 2 on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experimen ts with small Betula pendula plants, in which the concept of steady-st ate nutrition has been applied. Three distinctly different dry matter allocation patterns were observed when growth was limited by the avail ability of mineral nutrients: 1, Root growth was favoured when N, P or S were the major growth constraints. 2, The opposite pattern obtained when K, Mg and Mn restricted growth. 3, Shortage of Ca, Fe and Zn had almost no effect on the shoot:root ratio. The light regime had no eff ect on dry matter allocation except at very low photon flux densities (< 6.5 mol m(-2) day(-1)), in which a small decrease in the root fract ion was observed. Shortage of CO2 on the other hand, strongly decrease d root development, while an increase of the atmospheric CO2 concentra tion had no influence on dry matter partitioning. An increased allocat ion of dry matter to below-ground parts was associated with an increas ed amount of starch in the tissues. Depletion of the carbohydrate stor es occurred under all conditions in which root development was inhibit ed. It is concluded that the internal balance between labile nitrogen and carbon in the root and the shoot system determines how dry matter is being partitioned in the plant. The consistency of this statement w ith literature data and existing models for shoot:root regulation is e xamined.