Quantifying total phosphorus accumulation below-ground by canola and lupin plants using ³³P-labelling

Abstract

Background and aims: Measures of phosphorus (P) in roots recovered from soil underestimate total P accumulation below-ground by crop species since they do not account for P in unrecovered (e.g., fine) root materials. ³³P-labelling of plant root systems may allow more accurate estimation of below-ground P input by plants. Methods: Using a stem wick-feeding technique ³³P-labelled phosphoric acid was fed in situ to canola (Brassica napus) and lupin (Lupinus angustifolius) grown in sand or loam soils in sealed pots. Results: Recovery of ³³P was 93% in the plant-soil system and 7% was sorbed to the wick. Significantly more ³³P was allocated below-ground than to shoots for both species with 59-90% of ³³P measured in recovered roots plus bulk and rhizosphere soil. ³³P in recovered roots was higher in canola than lupin regardless of soil type. The proportion of ³³P detected in soil was greater for lupin than canola grown in sand and loam (37 and 73% lupin, 20 and 23% canola, respectively). Estimated total below-ground P accumulation by both species was at least twice that of recovered root P and was a greater proportion of total plant P for lupin than canola. Conclusion: Labelling roots using ³³P via stem feeding can empower quantitative estimates of total below-ground plant P and root dry matter accumulation which can improve our understanding of P distribution in soil-plant systems.