External Boron Requirements for Canola ( Brassica napus L.) in Boron Buffered Solution Culture

Author： Asad A. Bell R.W. dell B. Huang L.

ISSN： 0305-7364

Source： Annals of Botany, Vol.80, Iss.1, 1997-07, pp. : 65-73

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Abstract

Quantitative relationships between external boron concentrations that could elicit boron deficiency and plant growth, boron uptake rate, and plant boron concentrations have not been previously investigated due to the lack of water culture systems that provide satisfactory control over solution boron concentrations. Two approaches were tested to buffer the boron concentrations in nutrient solutions: supplying different amounts of boron saturated resin Amberlite IRA 743 per unit solution volume; and loading the resin with boron at 1 to 100% of full saturation. Mean boron concentrations (mu M ) ranged from 0.17 to 2.85 and from 0.047 to 27.03 in the two approaches, respectively, and in individual pots with plants solutions remained constant in boron concentrations for at least 10 to 12 d.At solution boron concentrations from 0.04 to 0.3 mu M , canola ( Brassica napus L.) plants remained alive, but shoot and root growth was stunted and showed classical boron deficiency symptoms. Increasing solution boron concentrations progressively increased boron concentrations in shoots and roots. Boron concentrations in roots were less than one-third of those in lower shoots, and less than those in upper shoots, except in boron deficient plants. In boron buffered solutions, dry matter of canola at both 12 and 24 d increased with increasing solution boron concentration up to 0.54-0.87 mu M . With increasing solution boron concentrations up to 26.5 mu M there was no further increase in dry matter, and no detrimental effects on plant growth. At 0.04 mu M boron, plants absorbed no boron from solution. Increasing solution boron concentrations from 0.1 to 26.5 mu M increased relative boron uptake rates from 0.005 to 0.1 mumol g -1 root f.wt d -1 . Maximum root efficiency, defined as relative uptake rate divided by the solution boron concentration, was achieved at 0.04 to 0.3 mu M boron in solution. With increasing solution boron concentrations, relative uptake rates of calcium decreased from 248 to 10 mumol g -1 root f.wt. d -1 . The results suggest that boron specifically inhibits calcium absorption.