DIURNAL CHANGES IN STEM DIAMETER AND PLANT WATER CONTENT IN PEACH TREES.

Three to five year-old peach trees (Prunus Persica L. Batsch cv. 'Maycrest') grafted on Prunus 'Damas 1869' grown in a sand trench were removed in the spring and grown hydroponically from then on for several months. The growing system comprised 2 balances continuously recording the mass of the nutrient solution and that of the tree, in order to estimate separately both transpiration and water uptake rates. Diurnal variation in plant water content (transpiration minus water uptake) was observed, with rapidly decreasing values when the solar radiation increased, while the reverse occurred when radiation decreased. Changes in stem diameter were continuously recorded using Linear Variable Differential Transformers. Data collected over several days of well contrasted climatic conditions revealed that rapid changes in the stem diameter occurred throughout the day and were closely related to plant water content without any important lag.