The Effect of Nitrogen Supply to Urtica dioica L. Plants on the Distribution of Assimilate Between Shoot and Roots

Abstract

In this study the influence of nitrogen nutrition on the patterns of carbon distribution was investigated with Urtica dioica. The nettles were grown in sand culture at 3 levels of NO−3, namely 3 (low), 15 (medium) and 22 (high) mM. These levels encompassed a range within which nitrogen did not affect total biomass production. The ratio of root: shoot biomass of the low nitrogen plants was, however, significantly higher than that of the nettles grown at medium and high N supply. Carbon allocation from one leaf of each pair of leaves was examined after a 14CO2‐pulse and a subsequent 14C distribution period of one night. Only the youngest two leaf pairs did not export assimilates. Carbon (14C) export to the shoot apex and to the roots, as measured at the individual nodes responded to the nitrogen status: At medium and high nitrogen supply the 3rd, 4th and 5th leaf pairs exported to the shoot apex, while lower leaves exported to the root. At low nitrogen supply only the 3rd leaf exported towards the shoot apex. The results illustrate the plastic response of carbon distribution patterns to the nitrogen supply, even when net photosynthesis, carbon export from the source leaves and biomass production were not affected by the nitrogen supply to the plant.

Influence of different nutrient regimes on the regulation of carbon metabolism in Norway spruce [Picea abies (L.) Karst.] seedlings

“…The supply of macronutrients such as nitrogen or phosphorus affects plant growth and morphogenesis, especially with respect to biomass distribution between shoot and roots. At suboptimal levels of nitrogen and phosphorus relatively more biomass is apportioned to the roots than to the shoots (Fetene, Moller & Beck, 1993). Accordingly, we found a decreased shoot/root ratio under N-and P-limited conditions in the Norway spruce seedlings examined.…”

“…At suboptimal levels of nitrogen and phosphorus relatively more biomass is apportioned to the roots than to the shoots (Fetene, Moller & Beck, 1993). Accordingly, we found a decreased shoot/root ratio under N-and P-limited conditions in the Norway spruce seedlings examined.…”

Reversal of the Direction of Photosynthate Allocation in Urtica dioica L. Plants by Increasing Cytokinin Import into the Shoot

“…For the calculation of that root/shoot carbon allocation ratio [ 14e (RIS)], radiocarbon in the internodes above the treated leaf was considered to be on its way to the growing parts of the shoot apex and thus was added to their 14e-content while 14e in the stem below that leaf was ascribed to the action of the root sink. As explained in the associated paper (Fetene et al, 1993) the 14econtent of the petiole and of the internode subtending the treated leaf due to the course of the leaf vascular bundles could not be attributed to any of the sinks. nettle (Wagner and Beck, 1993).…”

“…As only a minor part ofthe root system was cut off, 14C allocation in the controls was close to the natural pattern. This is indicated by the similarity between the carbon distribution ratios [ 14C (R/S)] of the controls on the one hand and of intact nettles which were grown at the same level of nutrient supply on the other (0.08 vs 0.10 at the fourth leaves and 54.4 vs 37.7, at the sixth leaves; see Fetene et al, 1993). The cut root stumps neither incorporated much radiocarbon for wound healing nor exuded 14C into the supplied ZR solution.…”

“…A positive correlation was established between the cytokinin gain of the shoot and the R/S (Wagner and Beck, 1993). In a preceding communication (Fetene et al, 1993) growth of Urtica dioica at different levels of nitrogen supply has been described in terms of sink-strength relations. Thus, the correlations between the N status of the plants Although young fruits (Bottomley et al, 1963) and leaves (Salama and Wareing.…”