Efficiency of N use by wheat as a function of influx and efflux of NO sub 3

Since N assimilation is one of the most costly functions of a plant, its efflux before assimilation results in a serious energy cost and loss in efficiency which could decrease yields. Efficient crop production is critical to the Controlled Ecological Life-Support System (CELSS). The objective is to determine the extent of efflux of the N species NO3(-), NH4(+), NO2(-), and urea after uptake, and possible means of regulation. It was found that NO3(-) efflux became serious as its substrate level increased. Efflux/Influx (E/I) of 3NO3(-) was greater in darkness (35 pct) than in light (14 pct) and the ratio greatly increased with increased substrate NO3(-), (up to 45 pct at 10 mM). It seems advantageous to use the lowest possible nutrient concentration of NO3(-). The feasibility of using ClO3(-) as a trapping agent (competitive inhibitor of NO3(-) uptake) for effluxed NO3(-) was assessed and its toxicity determined