Studies on Leaf Water Stress in Fruit Trees
I. Evaluation of the Pressure Chamber Method for Estimating Leaf Water Potential of Satsuma Mandarin Trees
1974 Volume 43 Issue 1 Pages 7-14
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1974 Volume 43 Issue 1 Pages 7-14
This paper presents an evaluation of the pressure chamber method for estimating leaf water potential (ψ) of Satsuma mandarin (Citrus unshiu MARC.) trees growing in both pots and field. Results obtained are as follows.
1. The rate of pressure increase within the range from 0.2 to 0.6atm/sec did not affect the estimating of ψ. In this study, therefore, the pressure was increased at the rate of 0.35atm/sec.
2. There was very little difference in potential between a leafy shoot and the leaves attached on the same shoot. This result shows that xylem pressure potentials in the shoot and petiole may be at dynamic equilibrium, and that number of replications would be reducible with the same precision by using shoots in place of individual leaves.
3. Main sources of variation in ψ in a tree were attributed to leaf age and to the radiation to which the leaves were exposed. As the radiation decreased by means of shading treatments, ψ increased rapidly. It was deduced that fluctuations of leaf temperature in response to changes in solar radiation must cause changes in ΔC (difference in water vapor concentrations between the leaf surface and the ambient air) which has a very large effect on transpiration rate. Variation of ψ in the day time was very large, as the differences of microclimatic conditions surrounding individual leaves may influence ψ through the effects on transpiration rate. Variance of ψ measured before sunrise was so small, resulted from minimal transpiration rate that the number of samples necessary for a precision of 0.5atm was only about three leaves.
4. When soil matric potential at the 15cm depth was higher than -1atm (less negative), ψ (ψmax) measured before sunrise was linearly correlated (r=0.977) with soil matric potential. When soil matric potential was less than -1atm (more negative), ψmax was curvilinearly related to glass-block resistance value. The results of this experiment indicate that ψ at night reflected soil moisture stress. During the daytime, however, ψ and soil water tension were not well correlated, because plant water status in mid-day was influenced by environmental factors.
In conclusion, it is quite clear that for Satsuma mandarin trees, the pressure chamber is a useful tool for measuring ψ rapidly and precisely in the field as well as in the laboratory.
