In situ 33P-labelling of canola and lupin to estimate total phosphorus accumulation in the root system
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Accurate quantification of P accumulated in plant root systems is difficult since fine roots are often not recovered from soil. 33P-labelling of plant root systems in soil may facilitate estimation of total below-ground P accumulation.
Canola (Brassica napus) and lupin (Lupinus angustifolius), grown in sand in sealed pots, were fed 33P-labelled phosphoric acid via the stem using a wick-feeding technique.
More 33P was partitioned to canola roots (51 %) than lupin roots (26 %), although specific activity of roots for the two species was similar (30–31 kBq 33P mg 31P−1) since canola roots had higher 31P content than lupin roots (4.1 cf 2.3 mg P plant−1). Mean recovery of fed 33P (250 kBq plant−1) in the whole plant including recovered roots was 84 % 10 days after feeding, and 6 % was sorbed to the wick. Assuming the unrecovered 10 % of 33P (below the detection limit for soil digestion method used in this study) was within fine roots, then estimated P in unrecovered fine roots represented 15 % of total root system P for canola and 32 % for lupin.
Wick-feeding 33P via the stem can effectively label P in roots in situ and facilitate quantitative estimation of total P accumulation by plant root systems.
KeywordsBelow-ground P inputs 33P in situ stem wick-feeding 33P specific activity Fine roots Shoot: Root P ratio
The senior author thanks the Grains Research and Development Corporation for providing top up funding (GRS10026) to support this research and the University of Adelaide for an Australian Postgraduate Scholarship. We also thank CSIRO for use of their radioisotope laboratory facilities and access to a field site for soil collection.
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