Some effects of the nitrogen supply on growth and development of Cirsium arvense

Abstract

The influence of nitrogen nutrition on the growth and development of Canada thistle, Cirsium arvense (L.) Scop., was investigated by growing seedlings in sand culture under controlled conditions. A preliminary experiment showed that seedlings at the cotyledon stage were very susceptible to injury by high salt concentration; a 10 × dilution of Hoagland's solution was required for successful establishment. Nitrate-N at 210 ppm caused severe leaf necrosis and inhibition of shoot and root bud growth, but provision of ammonium-N eliminated these effects.When seedlings were supplied with NH4NO3 at levels that ranged from 5.25 to 420 ppm N, shoot dry weight and root bud growth increased up to 210 ppm but decreased at 420 ppm, probably as a result of ammonium toxicity. By clearing roots with lactic acid it was shown that while growth of the root buds increased with the N level, the number of buds initiated was significantly reduced. When plants were grown initially at a low N level, a subsequent increase in the N supply permitted the root buds to escape from inhibition and develop as leafy shoots. This response suggested that under the experimental conditions, bud inhibition was due to internal competition for a limiting N supply.