Regulation Of Root-Shoot Relations To Crop Water Use

Water availability is a major determinate of crop productivity in arid and semi-arid regions of the world, thus the high use efficiently of water should be center of the crop production in this regions. One solution to this problem is to irrigate in diy environment, i.e. to modify the environment to suit the crops. Another solution is to select and cultivate crops requiring less water for growth (increase crop water use efficiency), i.e. to modify the crop to suit the environment better. Water use efficiency (WUE) may be expressed at various level. A higher WUE at equal water uptake is a desirable trait for crop because, both in rain-fed and in irrigated crops, more biomass or yield will be produced with the available water. Therefore it is not surprising that there have been extensively studied in WUE of crop, but most is focused on the crop responses of shoot, root as a sensor of soil environment change, its effect on WUE is studied less. The present potted piped and field experiments were designed to investigate the effects of crop root behavior (root size .~ profile distribution.~ function .~ concentration of ABA in root xylem sap et al) and root-shoot relations on its WUE, using wheat evolution genotype with different ploidy chromosomes sets and different corn varieties (Zea May) under various water conditions. The major results are as follows: 1. The instantaneous water use efficiency at the leaf level (WUE1) and the long-term water use efficiency (WIJEI) at whole plant level of corn hybrid HuDan 4 is higher than that of its parent under severe drought because of relative lower ABA concentration in root xylem sap, larger root growth and root-shoot ratio, more root distribution in deeper soil layer and higher root hydraulic conductivity(Lp) compared with its parent, which result in higher stomatal conductance ((is) and photosynthesis rate (Pn); WUE1 of HuDan 4 is higher than that of its parent under moderate and irrigated conditions, but its WIJEi is lower than that of parent because of large root growth and higher root hydraulic conductivity which is advantageous to water uptake of root and transpiration loss of leaf. 2. Stomatal behaviour of corn is controlled integratedly by both leaf water status and ABA concentration in root xylem sap under drought conditions , but it is more closely related to ABA concentration in root xylem sap than to the leaf water status. (is of corn decrease with increase of pH in root xylem sap. Pn and transpiration rate (Tr) of corn leaf is parabolic correlated with ABA concentration in root xylem sap. WUEi is also parabola correlated with ABA concentration in xylem sap because the sensitivity of Pn and Tr to ABA concentration in root xylem sap is different. Under long terni drought conditions, corn biomass, yield and WUEI are negative correlated with ABA concentration in root xylem sap, they decrease with the increase of ABA concentration in root xylem IV sap, and the sensitivity of yield WUEI to ABA concentration in root xylem sap are larger than that of biomass WUEI, although the effect of ABA concentration in root xylem sap to biomass production is larger than that to yield. Meanwhile, root growth of corn is reduced by ABA, but its decrease is less than that of biomass. The sensitivity of different corn varieties to ABA concentration in root xylem sap is different, its order is HuDan 4 473?han 4. Therefore, it is possible to increase WIJE by regulating ABA concentration in root xylem sap. 3. Pn and Tr of cont leaf is linearity correlated with its root hydraulic conductivity (Lp), both i...