Low seed phosphorus concentration depresses early growth and nodulation of narrow‐leafed Lupin (Lupinus angustifoliuscv. Gungurru)

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Abstract
Narrow‐leafed lupin (Lupinus angustifolius L.) seed with phosphorus (P) concentrations of 0.21, 0.26 or 0.43% were graded to uniform size (128 ± 5 mg) and grown in two glasshouse experiments to examine the effects of seed P concentration on early shoot, root and nodule growth, and its response to external P supply. Four days after imbibing seeds for a solution culture experiment, whole plant fresh weight (FW) of plants grown from low P seed (0.21%) was depressed compared to that from medium (0.26%) or high (0.43%) P seed. This depression in whole plant FW from growing low P seed persisted to final harvest at day 32 for levels of solution P supply ranging from nil to luxury levels. However, at adequate and luxury levels of solution P relative growth rates of plants grown from low P seed recovered from day 6 onwards to equal those of plants grown from medium and high P seed. In deficient‐P treatments, low P in seed strongly depressed root length, especially that of lateral roots which it did largely by decreasing their number. Low P in seed depressed nodule number and mass at all levels of external P supply but to a greater extent where P supply was deficient for growth. In these deficient‐P treatments, N concentrations in shoots were decreased slightly in plants from low P seed. Seed P may be specifically involved in the early stages of nodule development in lupins. In a P‐deficient loam and a P‐adequate sand, low P in seed depressed early shoot and root growth and nodule formation as it did in solutions. We conclude that low P concentration in lupin seed may limit successful crop establishment of lupins in the field, especially when P is deficient for plant growth or seedlings are subject to early stresses.

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