Water Relationships and Incorporation of 14C Assimilates in Tubers of Potato Plants Differing in Potassium Nutrition

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Abstract
Potato (S. tuberosum L. cv. Saturna) plants were grown in pots with varying supplies of K fertilizer (1.25, 5 and 10 g K2O/12 kg soil). Four weeks after midflower, plants were supplied with 14CO2 for 12 h and osmotic and water potential in tubers were determined. Assimilation of 14CO2 increased from 504 (K1)-1860 (K5) and 1922 kbecquerels/plant/12 h (K10). In all treatments, about 1/2 of the 14C was translocated to the tubers within 12 h, although calculated turgor pressure in tubers which could be considered as a potential counter-pressure to phloem unloading increased from + 5.3 (K1)-+5.9 (K5) and +6.0 bars (K10), respectively. Incorporation of 14C/gram tuber dry weight as well as /gram tuber starch was significantly higher in K5 than in K1 and slightly increased even further in the K10 treatment, where tuber pressure sap contained the highest K concentration (179 mm K).
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