Using Deuterium And Oxygen-18 Isotopes To Study Field Water Transformation In GSPAC

Quantification of water interaction among the Soil-Plant-Atmosphere-Continuum(SPAC)interfaces is crucial to improve water and nitrogen use efficiency.Root water uptake plays an essential role in water and nutrient transport in SPAC.Identify the root water uptake sources can give important implications for optimizing irrigation and fertilization management.In this study,we quantified the contribution of soil water at different depths to water uptake by winter wheat.Seasonal variations in water uptake patterns under different irrigation and fertilization treatments were compared during the experimental years.Furthermore,the relationship between winter wheat water uptake with soil moisture distribution were analyzed.Water content in the surface 0-30 cm have greater volatility in the water content profile of two seasons.Generally,moisture content was distributed horizontally in other depths and moisture content gradually increased to the deep layers.In 2014 season,water content below 50 cm is greater than 2015 season.In T5 treatment of the two seasons,moisture content in greater than other treatment in 20-90 cm soil because of the three irrigations in greening,jointing and grain-filling stage.The Local Mean Water Lines are ?D=7.3775?18O+4.0776,R2=0.9656 ??D=6.9632?18O+1.7862,R2=0.9663 in 2014 and 2015 season respectively.The fitting line of ?D and ?18O in soil water during two seasons are ?D=3.7742?18O-28.769,R2=0.405.There were different winter wheat stem water isotope distribute character between the two seasons.The slope of 2014 stem water's fitting line is greater than 2015 season under the influence of different soil water isotope.Generally,the water uptake of winter wheat gradually decreased to the deep layers.Due to different irrigation schedules at jointing and heading stages,variation of root water uptake patterns was significantly different between two growing seasons.Roots can use more water in layers having greater moisture content.Comparing to 2015 winter wheat,2014 winter wheat use more water from below 50 cm because of the greater water content in this depth range.The most significant difference of water uptake patterns among five treatments occurred at the grain filling stage.The deepest uptake depth was close to 120 cm but the shallowest was less than 50 cm.The changing trend of the main water uptake depth was that increased from shallow to deep layers at the first four growth stages,but it became shallow again at maturity stage.The soil moisture in the profile deceased notably when the water uptake depth extended below 50 cm.Transpiration in the treatments without irrigation was more stable comparing with the treatments with irrigation and the ratio of transpiration to evapotranspiration is relatively low.T/ET could reach up to 92.3% in the treatments with irrigation.Instead,the greatest T/ET in the treatments without irrigation is 79%.The amount of irrigation can affect the ratio of transpiration or transpiration in the proportion of evapotranspiration.