Physiological Response of Transpiration Efficiency of Winter Wheat to Soil Moisture

Pot experiment was conducted to study the response of transpiration efficiency of two ecotypes of winter wheat varieties(Shijiazhuang8;Luohan2) and its physiological mechanism to three different soil moisture conditions(L:60%-65% of field capacity;M:70%-75% of field capacity;H:80%-85% of field capacity).The results showed that leaf water potential decreased,and the root shoot ratio increased with the decreasing of soil moisture,but there was no significant difference between the two varieties.Lowering soil water content resulted in a reduction of biomass and water use for transpiration,however the transpiration efficiency at plant level was increased,it was increased by 119.0% and 62.2% for Shijiazhuang8 and Luohan2 in L treatment.With soil moisture decreasing,leaf photosynthetic rate and transpiration rate was reduced continuously,but transpiration efficiency at leaf level increased.There was a significantly positive correlation between the transpiration efficiency at plant level and at leaf level(R2=0.96).Stomatal conductance was reduced with the soil moisture lowing,and it significantly positive related to transpiration rate(R2=0.97),which indicated that transpiration was mainly regulated by stomatal factor;while photosynthetic rate reduced and intercellular CO2 concentration raised,which indicated that photosynthesis was mainly adjusted by non-stomatal factors.Such regulating mechanism makes more efficient use of water in the plant under lower level of soil moisture conditions.The preliminary results suggested that the different regulatory way of photosynthesis and transpiration constitute the physiological basis of higher transpiration efficiency under low soil moisture conditions.