Effects Of Different Nitrogen Forms And Combined With Plant Hormone On Growth, Nutrient Uptake And Their Distribution In Tobacco Plants

The effect of different nitrogen forms on tobacco (Nicotiana tabacum L. K326) growth, water uptake and transpiration, nutrients uptake and distribution and circulation of potassium was studied. The effect of plant hormone combined with different nitrogen forms on tobacco growth and nutrients uptake was also explored at the same time.Tobacco plants were treated by NO3"-N, NH4+-N, NH4NO3 or NH4+ +6-BA seperately in one experiment, and NO3"-N, NO3"-N+ABA, NH4+-N or NH/-N+6-BA in the other. During the study period in the first experiment, a symptom of NH4+ toxicity was observed obviously in the NH4+-N treated plants. The net dry weight increment of NH4"-N treated plants decreased by 57.8% compared with NO3"-fed plants. In both NO3~-N and NH4NO3 treatments, plants transpiration kept increasing during the study period and the major site of the transpiration located in the upper and middle leaves, whilst in NH4*-N treatment plants transpiration decreased from the day of the treatment and the middle leaves contributed the most to the total transpiration. NH/-N decreased significantly the uptake of K+, Ca *, Mg + and P, the ratio of these nutrients was 1.2:0.7:0.2:1, while the ratio of the same nutrients by NO3"-N treatment was 6.6:4.3:1.8:1. The net increment of K* content in different organs was different and that in lower leaves showed negative increment. The largest increment was found in the upper and middle leaves in NO3"-N treatment, and in the middle leaves in NH/-N treatment. NH4*-N relatively increased the amount of K+ recycled through the phloem. About 26.1% and 63.0% of the K* recycled in NO3"-N and NH/-N treatments, respectively.Foliar application of abscisic acid (ABA) to the plants supplied with NO3"-N made no difference as the uptake of K~, Mg2+ and P, when compared with NO3"-N treatment, though it decreased the transpiration of the plants. The same was also true as the52. 20026-benzylaminopurine (6-BA) was used in the NH4+-N treated plants.The amount of cytokinin in plants treated with NH4+-N decreased compared with that in NOs'-N treated plants, whilst the value of 8I3C increased. A conclusion may be made that stomata partly closed in NH4*-N treatment plants.