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Response of barley to hydrogen ion toxicity

W. Pondagee and W.J.R. Boyd

Faculty of Agriculture, University of Western Australia, Nedlands, W.A. 6009

Differences between barley cultivars have been reported for response to acid soils, but without identifying whether such differences are due to the direct effects of H+ ion toxicity or, to the indirect effects of reduced pH on nutrient availability. This paper reports on the effect of pH on the growth of roots of barley seedlings and of differencesbetween cultivars in the degree of injury sustained.

Methods

An aerated culture solution system was developed in which pH treatments could be maintained with minor adjustments every 24 hours combined with a complete change of the buffered nutrient solution every 48 or 72 hours. Treatments consisted of 4 plants of the same genotype per 2 litres of nutrient solution and these were replicated from 2 to 4 times. Measurements were made of total root length (TRL), root number (RN) and the length of the longest root (LRL).

Results and discussion

The critical level at which pH severely reduced root length was between 4 and 4.5 (Fig.1). Averaged over 6 experiments the effect of reducing pH from 6 to 4 reduced TRL by 35.1% (15.9) and LRL by 41.3% (14.6); where the SDs refer to variation between experiments. TRL was strongly correlated with LRL (r=0.95). Root numbers increased slightly (by 8.3%4.5) with reduction in pH from 6 to 4, doubled in number at pH 3.5 before falling off rapidly as pH decreased to 3.0 (Fig.1).

Figure 1 Response to solution pH in root number pl and of the length of the longest root (cms)

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Figure 2 Distribution of 10 genotypes for absolute length of the longest root at pH4 and root injury (percent)

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