Effect Of Water Stress On The Xylem Hydraulics Characteristic Of Different Apple Rootstock Seedlings And Grafted Seedlings

In this study, five types of three-year-old apple rootstock seedlings were used as toexperiment materials to explore effect of water stress on the xylem hydraulics characteristic ofdifferent apple rootstock seedlings. Three drought-tolerant varieties were Malus prunifolia(willd) Borkh, Malus robusta (Carr.) Rehd and Malus sieversii (Ledeb) Roem; twonon-drought-tolerant varieties were Malus hupehensis (Pamp) Rehd and Malus baccata (L.)Borkh. They were used to study the response of xylem embolism and hydraulic conductivityof apple rootstocks seedlings to drought stress by High Pressure Flow Meter (HPFM);Meanwhile, Fuji apple tree grafted on four types of interstock (dwarfed M9, semi-dwarfed M26and SH6, M.micromalus Makino seedlings) were used to study the response of hydraulicscharacteristic to drought stress.Results are as follows:1. The leaf special hydraulic conductance of canopy(Kl,canopy) of drought-tolerant andnon-drought-tolerant rootstocks both decreased to47.78%and32.96%of control on thecondition of moderate drought stress, while decreased to35.07%and16.91%of control tosevere drought stress. The leaf special hydraulic conductance of canopy (Kl,canopy) of MalusHupehensis (Pamp) Rehd changed most, reduced to14.9%.2. The leaf special hydraulic conductance of leaf (Kl,leaf) of drought-tolerant rootstockswere apparently higher than others in normal level. The leaf special hydraulic conductance ofleaf (Kl,leaf) of drought-tolerant and non-drought-tolerant rootstocks decreased to46.55%and34.27%of control to moderate drought stress, and decreased to26.11%and18.27%of controlto severe drought stress. Malus hupehensis (Pamp) Rehd changed most,while Malus sieversii(Ledeb) Roem changed smallest to drought stress.3. For drought-tolerant and non-drought-tolerant rootstocks, the ratio of hydraulicconductance resistance of root system to plant (Ratio=Rroot/Rplant) in differentdrought-tolerant ability rootstocks was61.89%and58.23%respectively. The hydraulicconductance resistance of root system of non-drought-tolerant rootstock Malus hupehensis(Pamp) Rehd changed fastest, and the hydraulic conductance resistance of root system ofMalus baccata (L.) Borkh changed most. Although the hydraulic conductance resistance of root system of drought-tolerant rootstocks was stronger than others, it changed lesser whenget drought stress.4. The leaf specific conductivity (Kl) of total plant, canopy, stem and root decreased withdrought stress, the trend of leaf specific conductivity (Kl) of each organ decreased asseedlings>semi-dwarfed seedlings>dwarfed seedlings. The range of dwarfed M9changedmost, while the vigorous stock changed smallest. Under normal condition, the canopy leafspecial hydraulic conductance of dwarfing rootstock M9grafted seedlings was67.5%of thevigorous stock grafted seedlings. In the same organs, the hydraulic conductance resistance ofcanopy in dwarfed plants was bigger than the vigorous stock seedlings. With theintensification of drought stress, the hydraulic conductance resistance of dwarfedmid-rootstocks increased, and flow velocity decreased, resulted to water deficit and waterpotential decrease, at the end, the percentage of leaf special hydraulic conductance of plant inseeding with M9grafted dwarfed plant was44.2%to severe drought.5. The leaf specific conductivity (Kl) of grafted union in dwarfed plant was lower thanvigorous stock plant; the changed trend is same to leaf specific conductivity (Kl) of canopy.The percentage of hydraulic conductance resistance of grafted union with plant (Ratio=Rgraft/Rplant) in plant was very small. Under well-watered condition, The ratio of hydraulicconductance resistance of dwarfed rootstock grafted union to plant in seedling, interstock M9,M26and SH6were4.07%,6.60%,4.97%and5.11%respectively, and to canopy in seedling,interstock M9, M26and SH6respectively were7.16%、11.40%、9.36%and10.02%.6. Among the hydraulic conductance resistance of each organ parts, the hydraulicconductance resistance of root system plays a very important role. The root sensibility ofwater stress was the highest. Under drought stress, the leaf specific conductivity (Kl) changedmost, while the leaf specific conductivity (Kl) of root system was the smallest among organs.