Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator Sedum plumbizincicola
Environmental Science and Pollution Research(2013)
摘要
The aims of this study are to investigate whether and how the nitrogen form (nitrate (NO 3 – ) versus ammonium (NH 4 + )) influences cadmium (Cd) uptake and translocation and subsequent Cd phytoextraction by the hyperaccumulator species Sedum plumbizincicola . Plants were grown hydroponically with N supplied as either NO 3 – or NH 4 + . Short-term (36 h) Cd uptake and translocation were determined innovatively and quantitatively using a positron-emitting 107 Cd tracer and positron-emitting tracer imaging system. The results show that the rates of Cd uptake by roots and transport to the shoots in the NO 3 – treatment were more rapid than in the NH 4 + treatment. After uptake for 36 h, 5.6 (0.056 μM) and 29.0 % (0.290 μM) of total Cd in the solution was non-absorbable in the NO 3 – and NH 4 + treatments, respectively. The local velocity of Cd transport was approximately 1.5-fold higher in roots (3.30 cm h −1 ) and 3.7-fold higher in shoots (10.10 cm h −1 ) of NO 3 – - than NH 4 + -fed plants. Autoradiographic analysis of 109 Cd reveals that NO 3 – nutrition enhanced Cd transportation from the main stem to branches and young leaves. Moreover, NO 3 – treatment increased Cd, Ca and K concentrations but inhibited Fe and P in the xylem sap. In a 21-day hydroponic culture, shoot biomass and Cd concentration were 1.51 and 2.63 times higher in NO 3 – - than in NH 4 + -fed plants. We conclude that compared with NH 4 + , NO 3 – promoted the major steps in the transport route followed by Cd from solution to shoots in S . plumbizincicola , namely its uptake by roots, xylem loading, root-to-shoot translocation in the xylem and uploading to the leaves. S . plumbizincicola prefers NO 3 – nutrition to NH 4 + for Cd phytoextraction.
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关键词
Ammonium,Cadmium,Nitrate,Positron-emitting tracer imaging system (PETIS),Sedum plumbizincicola,Transport,Uptake,Xylem sap
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