Influence of nitrogen nutrition on tuber quality of potato with special reference to the pathway of nitrate transport into tubers
2004
The influence of nitrogen (N) nutrition on tuber quality of potato (Solanum tuberosum L.), i.e., specific gravity, starch, nitrate, and protein content as well as ascorbic acid content was investigated in a pot experiment. As expected, specific gravity and starch content decreased with increasing fertilizer rates. Protein and especially nitrate content were positively related to nitrogen fertilization, while the effect on L-ascorbic acid content was relatively small. Only at the highest N level, which led to drastic yield depressions (3.8 g N pot(-1)), L-ascorbic acid content was significantly reduced. Since NO3(-) is considered phloem-immobile and xylem transport into the tubers is restricted (because of the tuber's low transpiration rate), the pathway of nitrate translocation into the tubers is unclear. For Ca(2+), a direct uptake from the soil solution by the tuber surface is well documented. In order to check whether this pathway may also be of importance for NO3(-), potato plants were cultivated in solution culture. The growing tubers were wrapped with paper tissue soaked with Ca(15NO3)2-labelled tuber medium, while contact of the tubers with the nonlabeled liquid growth medium was strictly avoided. 15N-content of tubers was measured on a mass spectrometer. The experiment demonstrated that with high NO3(-) concentration at the tuber surface, up to 40% of total tuber NO3(-) content can be taken up through the tuber skin.
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