Interactions between uptake of amino acids and inorganic nitrogen in wheat plants

[摘要] Soil-borne amino acids may constitute a source of nitrogen (N) for plants invarious terrestrial ecosystems but their importance for total N nutrition isunclear, particularly in nutrient-rich arable soils. One reason for thisuncertainty is lack of information on how the absorption of amino acids byplant roots is affected by the simultaneous presence of inorganic N forms.The objective of the present study was to study absorption of glycine (Gly)and glutamine (Gln) by wheat roots and their interactions with nitrate(NO₃⁻) and ammonium (NH₄⁺) during uptake. The underlyinghypothesis was that amino acids, when present in nutrient solution togetherwith inorganic N, may lead to down-regulation of the inorganic N uptake,thereby resulting in similar total N uptake rates. Amino acids were enrichedwith double-labelled ¹⁵N and ¹³C, while NO₃⁻ andNH₄⁺ acquisition was determined by their rate of removal from thenutrient solution surrounding the roots. The uptake rates of NO₃⁻and NH₄⁺ did not differ from each other and were generally abouttwice as high as the uptake rate of organic N when the different N formswere supplied separately in concentrations of 2 mM. Nevertheless,replacement of 50% of the inorganic N with organic N was able to restorethe N uptake to the same level as that in the presence of only inorganic N.Co-provision of NO₃⁻ did not affect glycine uptake, while thepresence of glycine down-regulated NO₃⁻ uptake. The ratio between¹³C and ¹⁵N were lower in shoots than in roots and also lower thanthe theoretical values, reflecting higher C losses via respiratory processescompared to N losses. It is concluded that organic N can constitute asignificant N-source for wheat plants and that there is an interactionbetween the uptake of inorganic and organic N.

[学科分类] 地球化学与岩石