CONICET | Buscador de Institutos y Recursos Humanos

Repeated defoliation and flooding can trigger opposite plant morphologies: prostrated and erect ones, respectively; while both induce the consumption of carbohydrate reserves to sustain plant recovery. This study is aimed at evaluating the effects of the combination of defoliation frequency and flooding on plant regrowth and crown reserves of Lotus tenuis, an important forage legume of flood-prone areas. Adult plants of L. tenuis were subjected to 40 d of flooding (4 cm water depth) in combination with increasing defoliation frequencies consisting in the clipping of shoot mass above water level (days 0 and 20). Responses in plant height, biomass of the different organs and utilization of water-soluble carbohydrates (WSCs) and starch in crowns were assessed. Flooding consistently increased plant height independently of defoliation frequency. This response was associated with a preferential location of shoot biomass above water level and with a reduction in root biomass accumulation. As a result, a second defoliation in the middle of the experiment was more intense in flood-taller plants, in which ca. 90% of their leaf biomass was removed against a 65% in non-flooded ones. The continuous de-submergence shoot response of frequently defoliated plants was attained at the expense of the depletion of their reserves. Consequently, these plants registered only 27.8% (of) WSCs and 9.1% (of) starch concentrations with respect to controls. Under such stressful conditions plants showed a marked reduction in their regrowth, as evidenced by the lowest biomass in all plant compartments: shoot, crowns and roots. In conclusion, it can be stated that increasing defoliation frequency negatively affects the tolerance of L. tenuis to flooding stress as a result of a trade-off between the common increase in plant height to emerge from water and the amount of shoot removed to tolerate defoliation. When both factors are combined and defoliation persists, plant regrowth is constrained by the depletion of crown reserves.