CONICET | Buscador de Institutos y Recursos Humanos

It is known that Lotus tenuis Waldst. & Kit. is able to tolerate flooding at lower evaporative demand typical of a winter-spring season. In this work, we report the plant water relations and growth of L. tenuis under more stressful conditions to plant growth, as a summer flooding. Adult plants of similar size of L. tenuis, extracted in soil blocks from a grassland of the Flooding Pampa (Argentina), were subjected to two treatments following a completely randomized design with five replicates: (1) control - watered to field capacity, and (2) flooded water level maintained at 6 cm above soil surface by 15 days. A subsequent 30 days grownperiod at drained conditions were allowed to evaluate plant recovery. Stomatal conductance (gs), transpiration rate (E) and leaf water potential (ψw) were registered every three days during flooding and every five days during the recovery phase. Plant harvest was carried out at the end of experiment and separated into shoot, crown and root compartments. Negative and progressive effects of flooding in gs, E and ψw occurred after a week of experimental period. At the end of flooding, flooded plants attained only 20-30% of the values of control plants in all physiological parameters. Interestingly, when flooding was discontinued, previously flooded plants recovered in one week their water status (Yw), and showed a stomatal behavior (gs) and transpiration rates (E) similar than controls. In spite of this higher capacity to recover their physiological parameters, plant growth of L. tenuis was negatively affected by this stress as revealed a 46% lower total biomass of flooded plants in comparison to control plants. In accordance, flooded plants of L. tenuis registered lower shoot, crown and root biomass than control plants (44%, 27% and 60%, respectively). In conclusion L. tenuis was able to tolerate two weeks of flooding at higher evaporative demand, typical of early summer season, but showing an important reduction in plant growth. This contrast with the typical response of L. tenuis at early spring, in which plants can adjust their physiological behavior in a way that plant biomass accumulation is not affected by flooding.