The aims of this study are to investigate whether and how the nitrogen form (nitrate (NO3 -) versus ammonium (NH4 +)) 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 NO3 - or NH4 +. Short-term (36 h) Cd uptake and translocation were determined innovatively and quantitatively using a positron-emitting 107Cd 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 NO3 - treatment were more rapid than in the NH4 + 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 NO3 - and NH4 + 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 NO3 -- than NH4 +-fed plants. Autoradiographic analysis of 109Cd reveals that NO3 - nutrition enhanced Cd transportation from the main stem to branches and young leaves. Moreover, NO3 - 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 NO3 -- than in NH4 +-fed plants. We conclude that compared with NH4 +, NO3 - 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 NO3 - nutrition to NH4 + for Cd phytoextraction.
- Positron-emitting tracer imaging system (PETIS)
- Sedum plumbizincicola
- Xylem sap
ASJC Scopus subject areas
- Environmental Chemistry
- Health, Toxicology and Mutagenesis