CONICET | Buscador de Institutos y Recursos Humanos

Waterlogging frequently reduces plant biomass allocation to roots. This response may result in a variety of alterations in mineral nutrition, which range from a proportional lowering of whole plant nutrient concentration as a result of unchanged uptake per unit root, to a maintenance of nutrient concentration by means of an increase in uptake per unit root. The first objective of this paper was to test these two alternative hypothetical responses. In a pot experiment, we evaluated how plant P concentration of Paspalum dilatatum, (a waterlogging- tolerant grass from the Flooding Pampa, Argentina) was affected by waterlogging and P supply and how this related to changes in root-shoot ratio. Under both soil P levels waterlogging reduced root-shoot ratios, but did not reduce P concentration. Thus, uptake of P per unit of root biomass increased under waterlogging. Our second objective was to test three non-exclusive hypotheses about potential mechanisms for this increase in P uptake. We hypothesized that the greater P uptake per unit of root biomass was a consequence of 1) an increase in soil P availability induced by waterlogging; 2) a change in root morphology, and/or 3) an increase in the intrinsic uptake capacity of each unit of root biomass. To test these hypotheses we evaluated a) changes in P availability induced by waterlogging; b) specific root length of waterlogged and control plants, and c) P uptake kinetics in excised roots from waterlogged and control plants. The results supported the three hypotheses. Soil P availability was higher during waterlogging periods, roots of waterlogged plants showed a morphology more favorable to nutrient uptake (finer roots) and these roots showed a higher physiological capacity to absorb P. The results suggest that both soil and plant mechanisms contributed to compensate, in terms of P nutrition, for the reduction in allocation to root growth. The rapid transformation of the P uptake system is likely an advantage for plants inhabiting frequently flooded environments with low P fertility, like the Flooding Pampa. This advantage would be one of the reasons for the increased relative abundance of P. dilatatum in the community after waterlogging periods

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