Effect of soil temperature on root resistance: implications for different trees under Mediterranean conditions

Abstract

The effect of temperature on radial root hydraulic specific resistance (Rp) is a known phenomenon; however, the impact of Rp variations expected from soil temperature changes over the tree root system is unknown. The present article analyses the relations hip of Rp with temperature in olive ‘Picual’ and a hybrid rootstock, GF677, at five different temperatures, showing that a variation of 3- and 4.5-folds exists for olive ‘Picual’ and GF677 in the range from 10 to 20 °C. The functions obtained were scaled up to show the theoretical changes of total radial root system resistance in a common tree orchard in a Mediterranean climate at a daily and seasonal scale, using recorded soil temperature values: a difference between summer and winter of 3.5-fold for olive ‘Picual’ and 9-fold for GF677 was observed. Nevertheless, Rp changes are not only related to temperature, as cavitation or circadian rhythms in aquaporin expression may also play a role. The results obtained from an experiment with the two cultivars submitted to constant pressure and temperature during several hours exhibited a variation in Rp, but this was of lower magnitude than that observed due to temperature changes. Finally, a comparison of Rp at 25 °C between GF677 and GN15 (another rootstock obtained from the same parental as GF677) showed significant differences. According to our results, diurnal and seasonal changes in Rp due to temperature variations are of significant importance, and it would therefore be advisable to assess them explicitly into soil–plant–atmosphere continuum models.