In situ 33P-labelling of canola and lupin to estimate total phosphorus accumulation in the root system

Abstract

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.