Effect of nitrogen supply on leaf growth, leaf nitrogen economy and photosynthetic capacity in potato

Literature reports show little effect of nitrogen supply on radiation use efficiency in potato and in other dicotyledonous C3 species. This paper tests the hypothesis that potato reduces leaf size rather than leaf nitrogen concentration and photosynthetic capacity when nitrogen is in short supply. Four pot experiments with different rates of nitrogen supply were conducted in glasshouses. For two leaf numbers measurements were made of leaf area, Pmax (rate of photosynthesis for saturating irradiance), specific leaf weight, and concentrations of total nitrogen and nitrate, all as a function of leaf age.Area per leaf was sensitive to nitrogen supply (about a factor 3 between extreme N treatments). Pmax declined with leaf age. There were no systematic effects of nitrogen supply on Pmax and on its change with leaf age, except that in some cases Pmax of leaves of high N treatments was lower than Pmax of low N treatments during part of the life span (leaf age of ca. 20-50 days). The dominant effect of nitrogen supply was on leaf size and not on Pmax or leaf N content. Pmax versus areal organic nitrogen concentration (gNm-2 leaf area) showed considerable scatter and, for a given nitrogen concentration, a slightly lower Pmax for high N treatments than for low N treatments. Comparison with other species showed a comparatively low value of Pmax in potato.