Effect of water stress on stem diameter changes of peach trees growing in the field.
Daily stem diameter changes were recorded continuously from June to September on peach trees (cv. Springcrest on GF 305 rootstock) irrigated at 50 and 100% of calculated maximum evapotranspiration. In addition, the stem water potential of these trees was measured several times. The maximum daily shrinkage (MDS) was dependent on environmental factors affecting plant transpiration, i.e. the soil water content (the single factor best explaining MDS variance) and the potential evapotranspiration. A multiple linear regression involving soil water content and potential evapotranspiration accounted for 66% of the MDS variance. The relationship between stem water potential and stem diameter changes during the course of the day showed a marked hysteresis with, for a given water potential, a greater diameter in the morning than in the afternoon. A minimum potential drop of 0.4 MPa compared with predawn value was necessary to induce onset of stem shrinkage. The reasons for this time lag between these two parameters are discussed. A good linear relationship was found (r2 = 0.83) between MDS and the minimum daily stem water potential of the day, suggesting that environmental conditions affect MDS through the mediation of plant water potential. The possibility of using stem diameter changes for irrigation purposes is briefly discussed.