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对田间生长的四年生桃树在充分灌水后的２２ ｄ 干旱周期内，分别在早上６∶００ 和中午１４∶００对茎、叶水势进行跟踪测定。同时测定了土壤充分湿润、中度水分亏缺及严重水分亏缺条件下上述指标的日变化。结果表明：在三种土壤水分条件下叶水势的变化幅度在０ ．２ ＭＰａ 左右，差异不明显；而午间茎水势则由土壤充分湿润时的－ ０．６ ＭＰａ 降至土壤水分严重亏缺时的－ １ ．８ ＭＰａ，下降了１ ．２ ＭＰａ。在整个干旱周期中，午间茎水势的变化虽受日蒸发量的影响，其变化趋势与土壤水势的变化趋势比较一致。随着干旱的加重，午间茎、叶水势之差即茎、叶水势梯度也出现极大变化。在土壤充分湿润时，茎叶水势梯度高达１ ．５ ＭＰａ，在土壤水分严重亏缺条件下，差异缩小为０。研究认为桃树外围新梢水势及茎、叶水势梯度的变化对土壤水分亏缺的反应比叶水势的变化更敏感，因此较适宜用作衡量果树水分亏缺程度的生理指标。
Four-year-old peach trees growing in the field were tracked to determine the stem and leaf water potential at 6:00 am and 2:00 pm, respectively, during the 22 d drought period after full irrigation. The diurnal changes of the above indexes were also measured under the conditions of fully moist soil, moderate water deficit and severe water deficit. The results showed that the change of leaf water potential was zero under three soil moisture conditions. 2 MPa, but the difference was not obvious. However, the midday stem water potential decreased from - 0.6 MPa when the soil was fully wetted to -1 when the soil water was severely deficient. 8 MPa, decreased by 1. 2 MPa. During the entire drought period, the change of stem-water potential in midday was influenced by daily evapotranspiration, and its change trend was consistent with that of soil water potential. With the aggravating of drought, the difference of stem-leaf and leaf-water potential in the midday, ie, stem and leaf water potential gradient also changed greatly. When the soil is fully moist, the water potential gradient of stems and leaves is as high as one. 5 MPa, the difference narrowed to zero under the conditions of severe soil moisture deficit. The results showed that the changes of shoot water potential and stem-leaf water potential gradient were more sensitive to soil water deficit than changes of leaf water potential. Therefore, it was more suitable to be used as physiological index to measure the water deficit of fruit trees.