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Besides leaves, non-foliar green organs such as stem and spike are also considered photosynthetic organs. To assess the photosynthetic contributions of these organs, the correlations between these photosynthetic areas and single-spike weight were investigated in a winter wheat (Triticum aestivum L.) under four nitrogen and mulching treatments: N120, N150, N195, and N195 + M. Two-year repeated field experiments were conducted on the Loess Plateau of China. Non-foliar photosynthetic area, grain-filling ratio and duration, grain yield, and in particular, single-spike weight, were measured, recorded and analyzed. Under the N195 + M treatment, plants showed the largest area of photosynthetic organs (flag leaf and non-foliar organs) and the highest grain yield and single spike weight. Single-spike weight was positively correlated with the areas of all examined non-foliar photosynthetic organs, in particular with the area above the flag leaf node (R2 = 0.761⁎) and the area above the exposed part of the peduncle (EXP) (R2 = 0.800⁎⁎). In addition, single-spike weight was highly correlated with average grain-filling ratio (R2 = 0.993⁎⁎), whereas it was less highly correlated with grain-filling duration (R2 = 0.533). The morphological traits of non-foliar photosynthetic organs were also more highly correlated with average grain-filling ratio than with average grain-filling duration. The significant correlation between each of the morphological traits (area, length and width) of EXP and single-spike weight indicates that morphological traits of EXP are important in determining spike weight in the Loess Plateau environment. Keywords: Grain-filling ratio, Grain-filling duration, Loess Plateau, Photosynthetic organs, Single spike weight, Winter wheat