CONICET | Buscador de Institutos y Recursos Humanos

This work is aimed at evaluating (1) submergence tolerance of seedlings of Lotus japonicus, L. corniculatus and L. tenuis and (2) recovery capacity of each species after floodwater subsides. Seedlings of these species were subjected to control and complete submergence conditions for 12 days (40 mm water depth), with a subsequent growth period of 30 days, under well-drained conditions, to evaluate their recovery. We assessed the following responses: seedling height, number of unfolded leaves, shoot and root biomass. In addition, the relationship between the shoot and root mass of seedlings of each species and treatment combinations were studied through linear regression. An increase in the slope of this relation between treatments would allow inferring a preferential active mass allocation toward shoots, typical of the low oxygen escape strategy. In contrast, a lack of variation on the slope of such relation, along with passive reductions in seedling growth would allow inferring a quiescence syndrome. Results showed that the Lotus species responded differentially to submergence in terms of seedling morphology and growth (submergence × species, P < 0.05). Seedlings of Lotus japonicus were able to grow during submergence period (i.e. escape strategy) while L. corniculatus and L. tenuis, responded to submergence by showing quiescence. In particular, L. japonicus increased seedling height by exposing its youngest leaf above water and increased the number of unfolded leaves underwater. Under submergence conditions, this species favored the biomass allocation towards shoot against roots as revealed by the higher slope for the relationship shoot: root when it was compared with the control seedlings (slope test, P < 0.01). These responses indicated the active escape strategy of this species. In contrast, submerged seedlings of L. corniculatus and L. tenuis showed the same number of unfolded leaves than at day 0, remaining below water level during all submergence period. These species neither increased their shoot and root biomass when submerged (P > 0.15 in all cases) nor changed the relationship between shoot and root mass between treatments (slope test, P > 0.4). Moreover, a reduction in cotyledons mass under submergence suggested that reserves in such organs were consumed to maintain a basal metabolism to deal with the energy crisis caused by the treatment. Taking these responses together, the idea of quiescence for L. corniculatus and L. tenuis seedlings due to submergence becomes apparent. Under control conditions all Lotus species increased by more than two-fold their height and by almost three-fold their biomass in comparison to the one registered at the beginning of the experiment (P < 0.05 in all cases). During the recovery period, species responded in an opposite direction than it could be expected from their performance during submergence. Lotus japonicus, which was able to grow during submergence, showed the lower recovery capacity as evaluated in terms of biomass accumulation. By the end of the experiment, previously submerged seedling of this species registered the lowest shoot biomass among the examined Lotus (60.3% and 54.4% lower mass in comparison to its controls). Such lower shoot biomass accumulation was associated, at least partially, with the lowest number of leaves per seedling as a result of the abscission of basal leaves that occurred after de-submergence. In contrast, root growth of L. japonicus was relatively less affected during recovery. L. corniculatus presented an intermediate recovery capacity after submergence as it was revealed by its higher shoot biomass accumulation and height increase between days 12 and 42 in comparison to the registered for L. japonicus. Remarkably, L. tenuis exhibited the highest recovery capacity of the three species tested. After the submergence, period in which they remained quiescent, seedlings of this species grew at a high rate, which allowed them to attain a similar height (P = 0.24) and shoot biomass (P = 0.19) than never-stressed controls by the end of experiment). Moreover, L. tenuis was the only species showing the same final number of unfolded leaves between treatments. In conclusion, for seedlings of the three Lotus species screened, the quiescence appears as a better strategy than escaping from water by shoot elongation in order to conserve energy for sustaining a high recovery after submergence. From an agronomic point of view, L. tenuis appears as a more successful species for seedling recruitment in natural grasslands prone to soil flooding due to its great recovery capacity after submergence.