THE SIGNIFICANCE OF PLANT ENERGY STATUS FOR THE UPTAKE AND INCORPORATION OF NH_4-NITROGEN BY YOUNG RICE PLANTS

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Uptake and assimilation of inorganic N in young rice plants has been studied with labelled N (N-15). Depletion of the plants' carbohydrate content, obtained by a preceding dark period, resulted in a drastic reduction of NH_4^+-N uptake. Plants exposed to low light intensity showed diminishing NH_4^+-N uptake rates as compared with plants exposed to full light intensity, the latter showing constant NH_4^+-N uptake rates during the whole experimental period. The percentage of labelled insoluble N in total labelled N was not significantly affected by a preceding dark period, whereas the low light intensity resulted in a lower proportion of insoluble N in roots and shoots. The incorporation of labelled N into the insoluble fraction (proteins, nucleic acids) was higher in plants fed with NH_4^+-N than in those fed with NO_3^-. The uptake of NH_4^+-N was not significantly affected by NO_3^-, whereas the NO_3^- uptake rate was considerably reduced in the presence of NH_4^+-N. Low energy status of plants affected the nitrate uptake more than the uptake of NH_4^+-N. The results show that uptake and assimilation of inorganic N depend much on the energetic status of plants. Nitrate uptake and assimilation is more sensitive to low energy conditions than NH_4^+-N.
一般社団法人日本土壌肥料学会の論文