The Mechanism Of Regulating Water Absorption Through Wheat Deep Rooting Under Varied Precipitation Distribution In The Loess Plateau

The precipitation in the Loess Plateau is low,the annual and inter-annual precipitation changes greatly,and the evaporation is greater than the precipitation,which makes the surface soil water content in this region less and unstable,while the deep soil water content is relatively high and stable.Therefore,it is of great significance to improve the crops water use efficiency by improving the absorption and utilization of deep soil water through roots in this region.Winter wheat is one of the main crops on the Loess Plateau,and water deficit is the main limiting factor for the yield of winter wheat.It is beneficial to improve the wheat efficient utilization of limited soil water by promoting the deep digging of wheat roots and regulating the utilization of soil water by roots.Therefore,it is proved that under different precipitation distribution,the way and mechanism of regulating water absorption by deep-root system of wheat are the theoretical basis for realizing efficient water use of wheat in loess Plateau and the practical demand for making cultivation management strategies according to local conditions in the Loess Plateau.This study was conducted in different types of dryland winter wheat root as the test materials during 2020-2021.A combination of field experiment and pot experiment were persued under different rainfall distribution,various varieties of wheat root zone water content,different soil characteristics of root system distribution,root anatomical structure and the change of the yield and water use efficiency,and combined with hydrogen and oxygen stable isotope tracer technique in order to reveal the mechanism of regulating water uptake by deep-roots under different precipitation distribution.The main conclusions are as follows:(1)Precipitation significantly affected soil moisture content in different soil layers,and soil moisture content in 0-20 cm root region was significantly affected by precipitation,and soil moisture content gradually decreased with the increase of the depth.There were significant differences in soil water content in root zone of different wheat varieties.The water content in root zone of shallow root type wheat was higher than that of deep root type wheat,and the water content in root zone of two deep-roots wheat was different.CK and CK-precipitation treatments at the late growth stage showed that the water content in root zone of CH58 was significantly higher than that of CH1.(2)There were significant differences in root depth,root distribution,root microstructure and root activity among wheat varieties under different precipitation treatments.The root depth of BM1 is 240 cm,and the root depth of CH58 and CH1 are 300 cm.The deep root biomass,root length density and root activity of shallow-root type wheat BM1 were significantly lower than those of deep root type wheat varieties.The comparison between the two deep-root wheat varieties showed that the deep-root biomass and root length density of 60-300 cm soil of CH1 Wheat were significantly higher than those of CH58,while CH58 had higher root activity,root diameter,cortex thickness and cortex thickness/diameter ratio,and lower root conduit diameter,which improved the water retention capacity of roots.It is beneficial for the root to absorb water and resist drought stress.(3)Under different precipitation conditions,wheat varieties mainly absorbed 0-20 cm soil water,and the contribution rate of deep soil water to wheat increased gradually with the decrease of precipitation.Under the same precipitation treatment,the soil water contribution rate of shallow-root type wheat was significantly higher than that of deep-root type wheat varieties at0-20 cm,and was significantly lower than that of deep-root type wheat varieties at 20-300 cm.Under the condition of low precipitation,the soil water contribution rate of 0-20 cm soil layer was higher than that of CH1,and the soil water contribution rate of 20-300 cm soil layer was slightly lower than that of CH1,but there was no significant difference in soil water contribution rate between the two wheat varieties.(4)Precipitation treatment significantly affected grain yield and water use efficiency of wheat.Compared with high precipitation treatment,low precipitation treatment decreased plant height,aboveground biomass,1000 grain weight,grain yield and water use efficiency of wheat varieties.There were significant differences in grain yield and water use efficiency among different wheat varieties.The grain yield and water use efficiency of shallow-root wheat were significantly lower than that of deep-root wheat under the same precipitation treatment.The comparison between the two deep-root type wheat cultivars showed that the grain yield of CH1 was significantly higher than that of CH58 due to its higher aboveground biomass under higher precipitation conditions,while the grain yield of CH1 was lower than that of CH58 under low precipitation conditions,but there was no significant difference.Therefore,it is suitable to plant CH1 wheat with more deeper root distribution and higher yield under CK+ precipitation conditions,while it is more suitable to plant CH58 wheat with higher root activity and higher drought tolerance under CK and CK-precipitation conditions.