[Relationship between soil water content and water use efficiency of apple leaves].

The relationship between soil water content and water use efficiency (WUE) of apple tree leaf was examined, and the mechanism of WUE variation was also studied by using pot-culture. The results showed that the WUE was upmost when soil water relative content (SWC) reached 52.0%. The increase of WUE when SWC decreased from 77.2% to 52.0% was mainly caused by the change of stomatal conductance. The decline of carboxylation efficiency resulted in the decrease of WUE when SWC decreased from 52.0% to 20.1%. The WUE returned up after being rewatered, but could not reach the control level within a week. The WUE decreased when the soil was waterlogged, but reached the control level in three days after being waterlogged. After the third day, the WUE decreased gradually with the extending of the time being waterlogged. On the sixth day being waterlogged, the carboxylation efficiency decreased.