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Root-water-uptake (RWU) is important for the simulations of soil water flow and nutrient transport in the soil-plant systems, and is usually linearly related to root length density.However, some researches have shown that the uptake activities of roots or various parts of roots (e.g., root tips, root hairs or fine roots) are different from each other.Higher root nitrogen content (RNC) was measured in younger roots, which were considered to be more active than older roots when extracting water.In this study, winter wheat (Triticum aestivum L.cv.Jingdong 8) were grown in nutrient solution (Exp.1) and soil columns (Exp.2) under controlled environmental conditions to investigate the relationship between RWU and root nitrogen mass (RNM).In Exp.1, 15 treatments were designed to examine the influence of nitrate concentrations (0.007-0.42 mg cm-3) and illumination conditions (free surface evaporation rates of 0.25-0.47 cm d-1) on root nitrogen contents and water uptake.The measurement information included the transpiration, dry weight, nitrogen content, root length of winter wheat, etc.In Exp.2, root nitrogen content and water uptake for wheat were measured under two nitrate levels (0.011 and 0.105 mg cm-3) and a low and high (80% field water capacity) soil water content regime.The distributions of soil water content, nitrate concentration, RNM density, root length density and soil temperature were observed.Results showed that the potential transpiration was proportional to RNM of winter wheat (R2 =0.99), and the maximum RWU rate S changing from 0 to 0.023 cm3 cm-3 d-1, was also linearly related to the RNM density (R2 =0.78).The ratio between the potential transpiration and RNM, namely the potential RWU coefficient per unit RNM,was independent of environmental nitrate level and the maturity of winter wheat, but changed linearly with the free water surface evaporation rate (R2-=0.88).The relationship between RWU and RNM was applied to simulate the distributions of soil water content, soil nitrate concentration and RNM density in Exp.2.The simulated results were comparatively well with the measured data, and the maximum root mean squared errors were 0.0085 cm3 cm-3, 0.0283 mg cm-3, and 0.0009 mg cm-3,respectively.