Specific absorption rates (SAR) and specific utilization rates (SUR) of sodium, chloride, potassium, calcium, magnesium and phosphate ions were determined for Melilotus segetalis (Brot.) Ser. (annual sweetclover) grown under both control and salinized conditions (NaCl treatment of CE=15 dS m−1) for a complete life cycle with sequential harvests. The behaviour over time of the SARs and SURs of the mineral elements was in general correlated with relative growth rate (RGR) kinetics, with a parabolic trend during the vegetative phase and a progressive linear decrease during the reproductive stage. Salinity significantly reduced the SARs of K and Mg but did not affect the SARs of Ca and P during the vegetative phase. During the reproductive stage, however, the SARs of K, Ca and P of salt‐stressed plants were higher than in control plants. The similar SARs of total cations (TC) found in control and salt‐stressed plants may indicate compensatory mechanisms to maintain a constant total cation content. Salt‐stressed plants showed lower SURs of K, Ca and P during the vegetative phase, and lower SURs of K and P but a higher SUR of Mg during the reproductive stage. A nutrient imbalance, caused by a lower root efficiency in absorbing K and Mg and a lower leaf efficiency in producing biomass per unit of K, Ca and P, apparently contributed to the salt‐induced reduction in growth during the vegetative phase of M. segetalis. The switch to non‐reduced, compensated growth during the reproductive phase may have been caused by a higher nutrient demand which increased the root efficiency in absorbing K, Ca and P and the leaf efficiency in utilizing Mg.

Annual sweetclover plants [Melilotus segetalis (Brot) Ser.] were grown for a complete life cycle with and without saline (NaCl treatment of CE=15 dS m−1). Growth and partitioning analyses were performed. Sequential harvests (every 15 d) during the life cycle, and separation of plant material into roots, stems, petioles, leaves and reproductive structures were carried out Salt treatment reduced growth during the early and middle stages of the life of the plant, but did not significantly affect RGR in the reproductive phase. The root–shoot allometric coefficient of salinized plants in the generative phase decreased more than in control plants. We suggest that salinity‐induced growth reduction in M. segetalis was primarily a result of a lower unit leaf rate (ULR) despite an increased leaf area ratio (LAR). Earlier flowering, higher biomass allocation to shoot and greater reproductive investment, but similar relative growth rate (RGR), were some of the main characteristics of salt‐stressed plants compared to controls during the reproductive phase, these apparently being associated with increased sink strength caused by developing flowers and fruits.

SUMMARYThe allocation of biomass and mineral elements (Na, K, Ca, P, N, Fe, Cu, Mn and Zn) during the ontogenetic cycle of annual sweetclover {Melilotus segetalis (Brot.) Ser,) growing under favourable and saline conditions bas been studied. Plants were grown in a glasshouse, in pots witb siliceous substrate and watered witb Hoagland solution. Half were salinized by adding 170molm"'' N^Cl (15 dS m"') to tbe solution. Eleven har\ests at ]5d inten'als measured tbe dry weigbt distribution within tbe plant and tbe mineral composition. Allocation relative to biomass (AKB) in eacb plant organ, botb under favourable and salt-stress conditions, was calculated for eacb mineral element. Biomass and mineral elements were allocated independently witbin M. segetalis, and tbe general pattern changed witb age and was affected by salinity. Salt-stressed plants were smaller and invested proportionaieh' more biomass in lea\'es. Na was accumulated in roots of young plants and excluded from leaves and fruits, wbereas K was depleted from roots and accumulated in leaves and fruits. Immobile Ca accumulated in leaves, with age, Phloeju-mobile P and X were translocated lo flowers and fruits. Fe. Cu and Zn were diluted in leaves and not affected b\-salt, wbereas Mn concentration increased with age and salinity. The switcb to reproduction and increased demand for nutrients induced drastic cbanges in tbe allocation pattern of mineral elements. Salinity induced a re-allocation of biomass and mineral elements in all plant organs except the reproductive structures, as part of a wbole-plant response to minimize salt toxic effects, to acbieve osmotic adjustment, to preserve tbe reproductive output, and to compensate nutrient imbalance.

Annual sweetcJover (Melilotus segetalis (Brot.) Ser. plants from the Guadalquivir salt marsh (S.W. Spain) were grown in a glasshouse, on sandy soil with nutrient solution and four salt treatments (O, 10, 50 and 100 mM NaC!). Plants (five replicates per treatment and age) were harvested at 50, 90 and 120 days after germinatíon. Sodium, chloride and potassium were determined for each plant in leaves, stems and roots. Total dry weight reduction with salinity was associated with increasing levels of sodium and chloride in plants and decreasing potassium uptake.