CONICET | Buscador de Institutos y Recursos Humanos

Our aim was to assess a series of response variables that characterize the water relations, the tissue aeration and the growth of the plants of Lotus glaber and Paspalum dilatatum when they are simultaneously affected by grazing and flooding. In this hypothesis we propose that L. glaber does not tolerate the simultaneous action of trampling, defoliation and flooding, such as the gramineous P. dilatatum. The following response variables were measured: a) leaf water potential (Lwp), b) stomatal conductance (gs), c) transpiration (E), at 3-5 day intervals, d) porosity of roots and shoots/sheaths, by pycnometry at the end of the flooding, e) time record of the height of 10 young shoots/tillers and f) number of green and dry shoots/tillers. The results showed an increase in the porosity of the roots and sheaths of P. dilatatum in the treatments with flooding or in the full interaction. Besides, in this species the greater values of Lwp, gs and E were recorded in the days of high atmospheric demand with respect to the control ones and, as from the 5th day of the flooding, the tillers were above water level. The number of tillers was lower with the trampling and increased with the defoliation, compared to the control ones, but there were no differences with respect to the flooding. The L. glaber plants with full interactive treatment died five days after the onset of the experiment. The ones that were only subject to flooding increased their porosity, in the roots and shoots, however they showed lower values of Lwp, gs and E along the time with respect to the control ones. Once the flooding was discontinued, such plants recovered. The control shoots of the L. glaber plants took three times less time than the flooded ones to reach the height that the water level had in the flooding treatment. In this species, trampling caused a decrease in the radical porosity and the quantity of shoots. This last variable was also reduced with the flooding but increased with the defoliation. It is concluded that flooding and grazing show a differential effect on these species, in their water relations and their growth, and that these responses would be related to the different tolerance that they express with respect to those disturbances.

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