The electrolyte leakage method can be misleading for assessing the frost hardiness of roots

Abstract

The relative electrolyte leakage (REL) method is often used to assess the frost hardiness of plant organs. However, testing the frost hardiness of roots with REL yields different results when the roots are frozen while remaining in the soil or in some other substrate than when REL follows a freezing test made on excised root segments. In this study, we show that the electrolytes may already leak out of injured roots during freeze/thaw treatment and during washing of the roots after the treatment. In this case, the conductivities measured after the freezing test and killing of the tissue both give lower readings than expected for injured samples, and hence the results of the REL are incorrect. We suggest that roots should be washed free of soil and placed in test tubes prior to the freezing test. The leakage of electrolytes from injured roots to soil may also limit the use of the REL method for measuring root viability.

Key words:

• Cold hardiness
• ion leakage
• Norway spruce
• REL
• root injury
• Scots pine

Acknowledgements

We thank Mervi Ahonpää for her technical assistance, Leena Karvinen for drawing the figures, and John Stotesbury for revision of the English. The study was funded by the Finnish Forest Research Institute (project 3394).