Nitrogen Compositional Changes in Xylem Exudate and Leaves of Burley Tobacco
- C. T. MacKown ,
- T. G. Sutton and
- L. P. Bush
Leaf nitrate accumulation occurs when nitrate transport to the leaf exceeds the assimilation rate of the leaf. Observed differences in leaf nitrate concentrations of hurley tobacco (Nicotiana tabacum L.) cultivars may be associated with differences in xylem exudate nitrate. Field studies during 2 yr compared xylem exudate and leaf N composition of low (LN) and high (HN) leaf nitrate-accumulating cultivars. In both years the LN, ‘KY15’, and the HN, ‘KY16’, were used; in the second year the HN, ‘Casey’, was added. The tobacco cultivars (main plots) were grown near Lexington, KY on a Maury silt loam (fine, mixed, mesic, Typic Paleudalf). Plants were sampled (subplots) beginning at the onset of linear growth and continuing until harvest. Leaf lamina nitrate averaged for three leaf positions and over all sampling dates was 287 and 455 mmol kg−1 for KY15 and KY16, respectively, in 1986 and 393, 551, and 580 mmol kg-1 for KY15, and KY16, and Casey, respectively, in 1987. Differences in lamina nitrate were not due to differences in tissue dry weight. Within each year, total N concentration of xylem exudate for each cultivar was relatively constant, even though nitrate decreased and reduced N increased over time. Average xylem exudate nitrate concentrations of the HN cultivars were 16 and 13% greater than KY15, while average lamina nitrate concentrations of the HN cultivars were 59 and 44% greater than KY15 in 1986 and 1987, respectively. Assuming similar transpiration rates among the cultivars, differences in leaf nitrate levels appear to be related primarily to leaf nitrate assimilation and only partly to cultivar differences in xylem exudate N composition.
Copyright © 1990.