Phosphorus speciation in mature wheat and canola plants as affected by phosphorus supply
Noack, Sarah R. | McLaughlin, Mike J. | Smernik, Ronald J. | McBeath, Therese M. | Armstrong, Roger D.
BACKGROUND AND AIMS: As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status. METHODS: Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha⁻¹equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution³¹P nuclear magnetic resonance (NMR) spectroscopy. RESULTS: Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate. CONCLUSIONS: Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status.
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