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

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.

Notes

Present address: Division of Forestry, CSIRO, Private Bag, P.O. Wembley, W.A., 6014, Australia.

Present address: School of Biological and Environmental Sciences, Murdoch University, Murdoch, W.A., 6150, Australia.