Studies On Mechanism Of Hydraulic Lift By Astragalus Adsurgens

Water can move from moist deep soil layers to drier shallow soil layers through the plant roots system(expecially transpiration ceases at night),this phenoment know as hydraulic lift.At present,the research on hydrauic lift of grazing is less,so this experiment studied hydrauic lift of Astragalus adsurgens by using split-root apparatus that upper pot fixed on the low pot.The results as follow:1.The hytraulic lift of Astragalus adsurgens was identified effectively by the split-root apparatus.The soil volumetric water content in upper pot was maitained 19.0±1.73%, when the soil volumetric water content and the soil water potential in upper pot were reached 14.9%,-1.28MPa respectively,the phenomenon of hydraulic lift occurred.After the plant tissues were cut,when the soil volumetric water content and the soil water potential in upper pot were reached 17.2%,-0.41MPa respectively,the phenomenon of hydraulic lift aslo occurred.The hydraulic-lift water is about 217g/6 plants,362g/6plants respectively.2.According to continuously observing,the soil volumetric water content and the soil water potential in upper pot declined from 7:00～16:00 and increased from 16:00～22:00 at the same time,they reached maximum at 22:00.After the plant tissues were cut,the soil volumetric water content and the soil water potential in upper pot declined from 7:00～16:00,at the 16:00 reached mixmum;and increased 16:00～7:00(the next morning),at the 7:00 reached maximum.3.When the phenomenon of hydraulic life of the Astragalus adsurgens oucced,the soil water potential in lower pot＞the root water potential in lower pot＞the root potential in upper pot＞the soil water potential in upper pot＞the leaf water potential.4.The changes about K~+,Na~+,soluble sugar and proline of roots were promoted that roots in lower pot absorbed water and protected the root in upper pot from hurting in daytime;and they mantained the difference betreen the root potential and the soil water potential in upper pot,thus the roots were facilitated and released water. 5.Astragalus adsurgens absorbed water from deeper soil layers by root systems,and released water to the drier shallow soil layers,these water was utilized by the Poa pratensis L and the water stress of the Poa pratensis L was alleviated.