Relationship of Water Use Efficiency with Photoassimilate Accumulation and Transport in Wheat under Deficit Irrigation

Deficit irrigation in winter wheat(Triticum aestivum L.) has been practiced in the areas with limited irrigation water resources.The objectives of this study were to(i) investigate the effect of different deficit irrigations on yield and water use efficiency(WUE);and(ii) understand the physiological mechanisms of drought resistance,water saving and high yield under deficit irrigation in wheat.A field experiment was conducted using four wheat(Jinmai 47 and Xifeng 20 in dryland,Shijiazhuang 8 and 4185 in dry-wet land) with the treatments of rainfed(T0),watering once at jointing(T1) and watering twice at jointing and anthesis(T2).The amount of irrigation is 60 mm each time.The physiological parameters measured included net photosynthetic rate(Pn),stomatal conductance(Gs),leaf area index,dry matter accumulation and partitioning,root distribution,yield components and water consumption,as well as the corelation between WUE and yield components.Non-irrigation before jointing and deficit irrigation from jointing to anthesis could significantly improve dry matter production and deep root development,and significantly save irrigation water.Both grain yield and WUE were conically related with water consumption.Non-irrigation significantly decreased dry matter accumulation and number of spikes.Low available soil water from booting to late grain filling resulted in the lowest biomass,grain yield,harvest index and WUE in T0 treatment.The increased yield in T1 and T2 was mainly contributed by the increased number of spikes,and seeds per spike.The increased WUE was mainly contributed by increased HI.Water stress during grain filling reduced Pn and Gs,and accelerated photosynthetic leaf senescence.However,the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains,significantly contributing the increased grain yield and HI.It is concluded that deficit irrigation between jointing and anthesis can change the root spread and develop deep root system,and significantly increase soil water use efficiency.Increasing both photosynthesis and photosynthetic duration,as well as increasing the remobilization of pre-anthesis carbon reserves and HI must increase wheat yield and WUE.