ALLOCATION OF BIOMASS AND MINERAL ELEMENTS IN MELILOTUS-SEGETALIS (ANNUAL SWEETCLOVER) - EFFECTS OF NACL SALINITY AND PLANT-AGE

The allocation of biomass and mineral elements (Na, K, Ca, P, N, Fe, C u, Mn and Zn) during the ontogenetic cycle of annual sweetclover (Meli lotus segetalis (Brot.) Ser.) growing under favourable and saline cond itions has been studied. Plants were grown in a glasshouse, in pots wi th siliceous substrate and watered with Hoagland solution. Half were s alinized by adding 170 mol m(-3) NaCl (15 dS m(-1)) to the solution. E leven harvests at 15 d intervals measured the dry weight distribution within the plant and the mineral composition. Allocation relative to b iomass (ARE) in each plant organ, both under favourable and salt-stres s conditions, was calculated for each mineral element. Biomass and min eral elements were allocated independently within M. segetalis, and th e general pattern changed with age and was affected by salinity. Salt- stressed plants were smaller and invested proportionately more biomass in leaves. Na was accumulated in roots of young plants and excluded f rom leaves and fruits, whereas K was depleted from roots and accumulat ed in leaves and fruits. Immobile Ca accumulated in leaves, with age. Phloem-mobile P and N were translocated to flowers and fruits. Fe, Cu and Zn were diluted in leaves and not affected by salt, whereas Mn con centration increased with age and salinity. The switch to reproduction and increased demand for nutrients induced drastic changes in the all ocation pattern of mineral elements. Salinity induced a re-allocation of biomass and mineral elements in all plant organs except the reprodu ctive structures, as part of a whole-plant response to minimize salt t oxic effects, to achieve osmotic adjustment, to preserve the reproduct ive output, and to compensate nutrient imbalance.