Low winter temperatures induce a disturbance of water relations in field olive trees

Abstract

Low winter temperatures induce an increase in the soil-to-trunk hydraulic resistance of field-grown olive trees resulting in a significant disturbance of their water relations. A disturbance of water relations in response to chilling have long been observed in potted plants growing under controlled conditions, but information is lacking for field plants. The aim of this study was to assess the effects of winter low temperatures on the water relations of mature olive trees. To this end, water potential, sap flux density, soil temperature and meteorological data were monitored in a hedgerow olive orchard near Córdoba, southern Spain, throughout two consecutive winters. Water stress symptoms were found in terms of midday Ψ, despite adequate water supply and low evaporative demand. These effects were associated with changes in the soil-to-trunk hydraulic resistance (R root), which increased by December–January to much higher values than those previously reported in the literature, particularly in the year of higher fruit load. The contribution of viscosity (η) to the observed R root dynamics was almost negligible as deduced from measurements of soil temperature, so the high winter values of R root were likely to have originated from other causes such as reductions in membrane permeability and root growth. The findings of this work raise new major issues that deserve further research such as the impact of the winter water stress on stomatal conductance and photosynthesis rates in mature olive trees.