Some effects of nitrogen nutrition on caesium uptake and translocation by species in the Poaceae, Asteraceae and Caryophyllidae

There is current interest in managing and manipulating 137Cs transfer from soil to plants. We hypothesized that N source might affect Cs uptake by plants and report experiments that confirm this. Uptake experiments using hydroponics with a variety of species in the Poaceae, Asteraceae and Caryophyllid clade grown in a variety of N regimes with excess N and then acutely exposed to Cs showed that N nutrition could affect Cs uptake rates, total amounts of Cs taken up and root:shoot ratios of Cs. In general, the Caryophyllids tested produced significantly less shoot and root biomass but had higher Cs uptake rates when grown on NH4+ rather than NO3−, whilst species from the Poaceae and Asteraceae almost always produced similar shoot and root biomass and had similar Cs uptake on NH4+, NO3− or glycine as N sources. This is the first time that plants grown on an organic-N source have been demonstrated to take up Cs. Physiological experiments using N-starvation and the N-metabolism inhibitor methionine sulfoxamine (MSX) demonstrated that Cs transport into the root was inversely related to NH4+ transport, i.e. NH4+-grown plants had higher Cs uptake rates if there is no NH4+ present during uptake but lower Cs uptake rates if NH4+ is present. It is suggested that taking account of N ecophysiology might help refine predictions of soil-to-plant transfer of 137Cs and, in some instances, be useful for managing or manipulating it. It is noted that there is much recent research into N nutrition in plants that might be useful in achieving this.