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 times; dilution of Hoagland's solution was required for successful establishment. Nitrate-N at 210ensp;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 NH4NO3at levels that ranged from 5.25 to 420ensp;ppm N, shoot dry weight and root bud growth increased up to 210ensp;ppm but decreased at 420ensp;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.
展开▼
