It is recommended that the cuticle be abraded while the leaf is still attached to the plant. This minimizes changes in leaf water potential that might be caused by the water loss during abrasion. The goal is to collect enough leaf tissue after abrasion to cover the entire bottom of the sample cup. The sample cup is 40 mm in diameter. If a single leaf (or disk cut from one leaf) will not cover the bottom of the cup, then several leaves may be used.
Abraded samples gave higher (less negative) water potentials overall in comparison with non-abraded samples. Because the abraded leaf tissue was still attached to the plant when the abrasion treatment was applied, it cannot be assumed that the wetting of the leaf surface resulted in the higher water potentials. All other treatment effects cause errors that lower water potential readings. We therefore conclude that the abraded measurements are most reliable. This was partially confirmed by freezing some samples for osmotic potential measurement. Upon freezing, the abraded samples showed a drop in the water potential, consistent with the release of turgor pressure while the non-abraded samples did not. We conclude that leaf abrasion is a practical method of speeding equilibration to obtain more accurate measurements of leaf water potential.
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