Effects of olive root warming on potassium transport and plant growth

Young olive (Olea europaea L.) plants generated from seed were grown in liquid hydroponic medium exposing the roots system for 33days or 24h to high temperature (37°C) while the aerial part to 25°C aiming to determine the prolonged and immediate effects of root warming on K⁺(Rb⁺) transport in the root and consequently on plant growth. The exposition of the root system to 37°C for 24h inhibited K⁺ (Rb⁺) transport from root to shoot having no effect on its uptake. However, when the root system was exposed permanently to 37°C both the K⁺ (Rb⁺) uptake and translocation to the aerial part were inhibited as well as the growth in all plants organs. The ability of the root system to recover K⁺ (Rb⁺) uptake and transport capacity after being exposed to high temperature was also evaluated. Plants grown in a root medium at 37°C for 31days were transferred to another at 25°C for 48 or 96h. The recovery of K⁺ (Rb⁺) root transport capacity after high root temperature was slow. Any signal of recovery was observed after 48h without stress: both potassium root uptake and subsequent transport to above organs were inhibited yet. Whereas 96h without stress led to restore potassium upward transport capacity although the uptake was partially inhibited yet. The results obtained in this study have shown that the root system of young olive plants is very sensitive to high temperature related to root potassium transport and growth of the plant. Taking into account the two processes involved in root potassium transport, the discharge of K⁺ to the xylem vessels was more affected than the uptake at the initial phase of high root temperature stress. However, it was the first process to be re-established during recovery. All this could explain the symptoms frequently observed in olive orchards when dry and high temperature spells occur: a reduction in shoots growth and leaves with low levels of potassium contents and dehydration symptoms.