1968 Volume 37 Issue 1 Pages 37-44
The experiments were carried out during 1962-1965, to clarify the daily and seasonal changes of the water saturation deficit (W. S. D.) of leaves, as an index of the degree of water deficit in Satsuma orange trees. And further observations were made on the relationship between W. S. D. of leaves, climatic factors and soil moisture. The results obtained were summarized as follows:
1. Daily changes of W.S.D. of leaves in summer were rose in a steady curve with sunrise, and maximum value was found to occur around noon, thereafter, values were gradually descended, and minimum value was observed around 6.00P.M. each day. On the other hand, its changes in winter were smaller than that in summer, although, the tendency was almost similar to that observed in summer.
2. On the seasonal changes of W.S.D. of leaves, during the period from early to late February, its values were definitely ascended, and it might be mainly due to the low temperature and cold wind. And its values in early February were found to have the highest in winter period, but thereafter to late March, W.S.D. of leaves were gradually descended. In early May, however, W.S.D. of leaves were ascended rapidly and formed a peak, it seemed to be closely related to the drought of spring and sprouting a current shoots, but thereafter to late June, its values were slightly descended. During the period from early July to late August, under the condition of high temperature and drought, W.S.D. of leaves were notably ascended, and the trend was most remarkable in early August, its values in this period were the highest one. W.S.D. of leaves in September were considerably high compared with that in October, thereafter from early October its values were descended.
3. In the winter half (Nov.-Apr.), W.S.D. of leaves had the high negative correlations with the air temperature, soil temperature, precipitation and saturation deficit of water vapour pressure. On the contrary, W.S.D. of leaves in the summer half (May-Oct.) had the high positive correlations with the air temperature, soil temperature and saturation deficit of water vapour pressure.
4. W.S.D. of leaves in autumn and winter were ascended with the increasing of cold wind velocity, also, its values were ascended with the increasing of hours of exposed to the cold wind. Further, velocity of transpiration stream in shoot was increased by the exposed to the cold wind, and its velocity was diminished with the decreasing of soil moisture.
5. W.S.D. of leaves in summer had a very high negative correlation with the soil moisture, therefore, by the use of curved regression equation, it was possible that the soil moisture is presumed with the W.S.D. of leaves. When the soil moisture was between field capacity and moisture equivalent, changes of W.S.D. of leaves were very small, and then W.S.D. of leaves were slowly ascended with the decreasing of soil moisture in less than moisture equivalent. Thereafter, its values were extremely ascended, being accompanied with a marked decreased of soil moisture to the wilting point. In addition, when the W.S.D. of leaves were reached 8.0 per cent, the trees showed visible symptoms of wilting in leaves, and its values reached 10.0 per cent, showed visible symptoms of wilting in fruits.
In the winter period, however, no correlation could be found between W.S.D. of leaves and soil moisture, accordingly, the ascension of W.S.D. of leaves in winter were might be mainly due to the climatic factors.