The measurement of plant water potential is considered to be a direct approach to confirming the irrigation time in present irrigation systems.In this current study,two shelter forests species in the Junggar Basin (Central Asia),Populus euphratica and P.Russkii Jabl,were studied.We monitored leaf water potential (ψl),stem water potential (ψs) and soil water potential (ψsoil) under different irrigation conditions.The characteristics of the variation in leaf and stem water potential (ψl and ψs) of P.euphratica and P.Russkii Jabl,as well as the impact of soil water potential (ψsoil) on the leaf and stem water potential (ψl and ψs) under different irrigation conditions were discussed.Our results showed the following.(1) With increased irrigation,the intensity of drought stress on P.euphratica and P.Russkii Jabl decreased.(2) The intensity of drought stress experienced was less for P.Russkii Jabl than for P.euphratica under the same irrigation conditions.(3) The more intense the drought,the less sensitive was P.Russkii Jabl,but the more sensitive was P.euphratica,and vice versa.(4) For the P.euphratica community the soil water potential (Ψsoil) at 60 cm depth responded to variation in irrigation more strongly than at 30 and 90 cm depths.For the P.Russkii Jabl community the soil water potential (ψsoil) in the shallow surface layer responded to irrigation variation more strongly than that in deep layers.(5) In the event of relatively sufficient soil water,predawn stem water potential (ψpds) of plant was a reasonable indicator reflecting soil water potential (ψsoil).(6) The water demand of P.euphratica and P.Russkii Jabl shelter forests can be met with different irrigation policies:large volume and less frequency for P.euphratica but small volume and more frequency for P.Russkii Jabl.
