干旱过程中桃树茎和叶水势的变化

Changes of Leaf and Stem Water Potential of Peach Tree in the Course of Soil Drying

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。

After well irrigated, the leaf and stem water potential in field grown peach trees were monitored both in the early of the morning or at midday for 22 days.In addition, the diurnal pattern of leaf and stem water potential on 3 dates which under different soil water statues were also obtained.On 3 different dates,the minimum(12∶00)and maximum leaf water potential(6∶00)were in the range of -1.8 MPa to -2.0 MPa and -0.6 MPa to -0.8 MPa.The differences were very limited.However,the differences of stem water potential under different soil water content were obvious.Under wet soil condition,the minimum and maximum stem water potential were -0.1 MPa and -0.6 MPa. Under severe soil water stress,they decreased to -0.4 MPa and -1.8 MPa.In the course of soil drying,the change of midday stem water potential was better related to the soil water conditions.The water potential gradient between leaf and stem had greater response to water stress.After well irrigation,the difference between midday leaf and stem water potential was as high as 1.5 MPa.As the soil drying,it was eventually disappeared.The result indicated that the midday stem water potential and the water potential gradient between leaf and stem are very sensitive to soil water deficit.