CONICET | Buscador de Institutos y Recursos Humanos

Our previous studies have shown that 40 -75 day-old Lotus tenuis plants were able to growth when they were subjected to moderate drought (166% of the permanent wilting point) or waterlogging. In the present study, the impact of a range of soil water deficit or excess on Lotus tenuis plantlets growth, arbuscular mycorrhiza (AM) symbiosis and Rhizobium nodulation was investigated in a saline-sodic soil (pH 9.4; electrical conductivity 5.2 dS/m; exchangeable sodium capacity 60%, permanent wilting point 12%, field capacity 34%). The plantlets were grown trays (5 cm depth; 340 cm3) in a greenhouse for 6 days (expanded cotyledons, EC plants) or 28 days (3rd open expanded leaf, 3L plants) after sowing at 75% of field capacity and then subjected to a range of water content in soil (15% - 40% w/w). In addition, pre-germinated seeds were sown (sow, SO plants) at the same range of water content in soil as for EC and 3H plants. After a total period of growth of 45 days after sowing, dry weight, chlorophyll and carotenes concentrations, arbuscular mycorrhizal colonization morphology and Rhizobium nodules in roots were measured. The dry weight of shoots and roots were higher in EC than in 3L plants at both water deficit (15-20%) and excess (30-40%). In EC plants shoot:root ratio was higher at water deficit but lower at water excess comparing with 3H plants. Chlorophyll concentration, root length and number of Rhizobium nodules per gram of fresh root showed a similar pattern that for the dry matter. They were higher in EC than in 3L plants at both water deficit (15-20%) and excess (30-40%) treatments. The lowest values of chlorophyll and carotenes concentrations in EC and 3H plants were found at 30-35% water content and associated with the highest values of electrical conductivity in soil. Leaves of these plants were pale green and chlorotic comparing with plants grown at severe deficit (15%) or waterlogging (40%) which were dark green. Soil pH consistently decreased with increasing water content. The SO plants did not growth at severe drought (15%) or waterlogging (40%). At the range of 20-35% of water content, the SO plants response followed a similar direction but a different pattern with respect to EC and 3L plants. There were four factors involved that interact among them in this experiment: a) the age of the plant when the range of soil water deficit or excess is applied, b) the potential water stress that plants may suffer during the initial period of growth (6 and 28 days) at 25% w/w, c) the amount of soil water available during the final period of growth (39 and 17 days respectively), and d) the potential soil water stress that plants may suffer during the final period of growth. Young plantlets (EC) showed a better adaptation than old plantlets (3H) to deficit or excess of water stresses in soil. This adaptation was associated to the longer of the period of growth that EC plants had before being subjected to water stress comparing to 3H plants. Severe drought in young plantlets (EC) depressed the total root length colonized and the arbuscular colonization with respect to old plantlets (3H), but waterlogging had an opposite effect. Vesicular colonization increased with increasing soil water content in both EC and 3H plants. Six day-old Lotus tenuis plantlets (EC) resisted both severe drought (15%) or waterlogging (40%) and produced more dry yield that 28 day-old plantlets grown in a saline-sodic soil. After sowing (SO), plantlets need to emerge their cotyledons to grow before being subjected to deficit or excess of water in soil. In addition, Lotus plantlets were able to associate symbiotically with AM fungi and Rhizobium bacterias at both stresses hydric condition in soil.