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• Aerenchymatous phellem (secondary aerenchyma) has rarely been studied in roots. Its formation and role in internal aeration were evaluated for Melilotus siculus, an annual legume of wet saline land. • Plants were grown for 21 d in aerated or stagnant (deoxygenated) agar solutions. Root porosity and maximum diameters were measured after 0, 7, 14 and 21 d of treatment. Phellem anatomy was studied and oxygen (O2) transport properties examined using methylene blue dye and root-sleeving O2 electrodes. • Interconnecting aerenchymatous phellem developed in hypocotyl, tap root and older laterals (but not in aerial shoots), with radial intercellular connections to steles. Porosity of main roots containing phellem was c. 25%; cross-sectional areas of this phellem were threefold greater for stagnant than for aerated treatments. Root radial O2 loss was significantly reduced by complete hypocotyl submergence; values approached zero after disruption of hypocotyl phellem below the waterline or, after shoot excision, by covering hypocotyl phellem in nontoxic cream. • Aerenchymatous phellem enables hypocotyl-to-root O2 transport in M. siculus. Phellem increases radially under stagnant conditions, and will contribute to waterlogging tolerance by enhancing root aeration. It seems likely that with hypocotyl submerged, O2 will diffuse via surface gas-films and internally from the shoot system. [ABSTRACT FROM AUTHOR]

The 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 has been studied. Plants were grown in a glasshouse, in pots with siliceous substrate- and watered with Hoagland solution. Half were salinized by adding 170 mol m-3 NaCl (15 dS m-1 to the solution. Eleven harvests at 15 d intervals measured the dry weight distribution within the plant and the mineral composition. Allocation relative to biomass (ARB) in each plant organ, both under favourable and salt-stress conditions, was calculated For each mineral element. Biomass and mineral elements were allocated independently within M. segetalis and the 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 from leaves and fruits, whereas K was depleted from roots and accumulated 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 concentration increased with age and salinity. The switch to reproduction and increased demand fur nutrients induced drastic changes in the 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 whole-plant response to minimize salt toxic effects, to achieve osmotic adjustment, to present the reproductive output, and to compensate nutrient imbalance. [ABSTRACT FROM AUTHOR]

The acidic and calcareous populations of Melilotus alba behave differently when grown in competition than when grown in isolation from each other. Thus, the acidic population which did well in both calcareous and acidic media in competition-free cultures, showed good growth yield in acidic soils only when in competition with the calcareous population. Further, the differences observed between the two populations in competition-free experiments became more pronounced when grown mixed. The time of introduction of either of the two populations into the mixture affects the final dry weight yield of the shoot, depending upon the soil type. In mixed cultures of the two populations, the calcareous population grown in an acidic soil and the acidic population grown in a calcareous soil responded by mortality of individuals, especially when the second population in each case was introduced earlier into the mixture. [ABSTRACT FROM AUTHOR]