Abstract
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 NH 4 + rather than NO 3 −, whilst species from the Poaceae and Asteraceae almost always produced similar shoot and root biomass and had similar Cs uptake on NH 4 +, NO 3 − 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 NH 4 + transport, i.e. NH 4 +-grown plants had higher Cs uptake rates if there is no NH 4 + present during uptake but lower Cs uptake rates if NH 4 + 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.
Highlights
Research into 137Cs transfer from soils to plants has recently begun to expand from making predictions of plant 137Cs concentrations to managing and manipulating them
Similar results have recently been reported with 137Cs uptake by rye grass
The experiments reported here were not designed as a single coherent set of experiments, and the details of their experimental conditions vary and make inter-comparisons difficult, but they do confirm that there can be some statistically significant effects of N-nutrition on Cs uptake by plants
Summary
Research into 137Cs transfer from soils to plants has recently begun to expand from making predictions of plant 137Cs concentrations to managing and manipulating them. Because there are currently no economically viable methods to clean up all 137Cs-contaminated soils, and enhanced plant uptake of other contaminants from soils is showing potential as a decontamination method Huang et al, 1998; Ma et al, 2001), ‘phytoextraction’ has Willey et al, 2001) These trials have shown that manipulations to enhance soil-to-plant transfer are needed if phytoextraction is to be useful for 137Cs. Evans and Dekker (1969) provided the first field test of this phenomenon and showed that additions of NH4+ to soil significantly increased 137Cs uptake by oat plants. Similar results have recently been reported with 137Cs uptake by rye grass
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