Mechanisms for the increase in phosphorus uptake of waterlogged plants: soil phosphorus availability, root morphology and uptake kinetics |
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Authors: | Gerardo Rubio Martín Oesterheld Carina R Alvarez Raúl S Lavado |
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Institution: | (1) Cát. Fertilidad y Fertilizantes, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417 Buenos Aires, Argentina Fax: (541) 522 8395; e-mail: gerub@ferlav.agro.uba.ar, AR;(2) IFEVA, Dep. Ecología, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina, AR |
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Abstract: | 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 of root biomass, to a maintenance of nutrient concentration by means of an increase in uptake per unit of
root biomass. 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 (1) changes in P availability induced by waterlogging; (2) specific root length of waterlogged
and control plants, and (3) P uptake kinetics in excised roots from waterlogged and control plants. The results supported
the three hypotheses. Soil P avail-ability 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.
Received: 15 February 1997 / Accepted: 20 May 1997 |
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Keywords: | Grasslands Mineral nutrition Allocation Phosphorus Adaptations |
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