Effects of Water Deficit on Phosphorus Nutrition of Tomato Plants

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Abstract
Measurements were made of phosphorus uptake by intact tomato plants from solutions labelled with 32P. The plants were exposed to low water potentials by the addition of mannitol to culture solutions. The amounts of labelled phosphorus in the roots and in the shoots wore determined after a one‐ or two‐hour period. Down to ‐5.4 atmospheres, the amount of labelled phosphorus in the roots remained constant, hut the amount transported to the shoots was reduced. However, potentials of ‐10.4 atm reduced the amount of labelled phosphorus in both the root and the shoot. Similar results were obtained when plants were tested immediately after water stress was imposed and when tested after water potentials had been lowered gradually.Plants were treated for one hour at low water potentials and then returned to control solutions (−0.4 atm). For a considerable time, these plants had a much lower phosphorus uptake than plants which had remained continuously at −0.4 atm. These data support the idea that a disturbance in mineral nutrition is partly responsible for reduced growth in plants which experience a moderate water deficit.
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