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Optimizing irrigation and nitrogen (N) fertilization cooperative application to coordinate the balance between agricultural production and ecological environment is a vital challenge for sustainable agricultural production. Here, a three-year field experiment was conducted from 2018 to 2020 in the semi-arid region of north China to investigate the effects of different irrigation amounts (W 1 , 50% ETc, ETc is the crop evapotranspiration; W 2 , 75% ETc; W 3 , 100% ETc; W 4 , 125% ETc) and nitrogen fertilization rates (F 1 , 75 kg·ha−1, F 2 , 150 kg·ha−1, F 3 , 225 kg·ha−1, F 4 , 300 kg·ha−1) on growth, yield, water and fertilizer use efficiency, and soil N residue of spring wheat by drip fertigation, and explore the optimal combination of irrigation amount and N fertilization rate based on a multi-objective optimization method. The results showed that leaf area index (LAI), dry matter accumulation, yield, water use efficiency (WUE) and economic return of spring wheat increased first and then decreased with increasing irrigation at the same level of N fertilization. These parameters peaked at W 3 , with W 1 performed poorly and low irrigation amount was detrimental to the function of fertilizer. At the same level of irrigation, LAI, dry matter accumulation, yield and economic return all demonstrated significant diminishing return effects with increasing N fertilization, whereas nitrogen partial factor productivity (NPFP) reduced with increasing N fertilization. Furthermore, with the simultaneous increase of irrigation and N fertilization, the accumulation of soil nitrate nitrogen (NO 3 -N) decreased in the 0 − 40 cm soil layer and increased in the 60 − 100 cm soil layer. The partial least squares path model (PLS-PM) revealed that irrigation had a direct positive effect on spring wheat yield rather than N fertilization, and irrigation had a direct negative effect on soil N residue. Based on the multi-objective optimization model established by multiple regression analysis and the elitist non-dominated sorting genetic algorithm (NSGA-II), the irrigation amount of 337.3–354.9 mm combined with the N fertilization rate of 181.2–198.6 kg·ha−1 could obtain the optimal comprehensive benefits of wheat yield, economic return, water and fertilizer utilization efficiency and environmental impact. This study can provide an important scientific basis for the management and optimization of irrigation and fertilization for spring wheat in semi-arid region of China and other similar regions around the world. • Irrigation had a direct positive effect on spring wheat yield rather than N fertilizer. • Excessive irrigation and N fertilizer increased soil nitrogen residue in deeper soil. • Water and nitrogen coupling improved economic return and reduced soil N residue. • The NSGA-II was applied to the optimization of irrigation and N fertilization. [ABSTRACT FROM AUTHOR]

Abstract: Taihu Basin is the most developed area in China, which economic development has resulted in pollutants being produced and discharged into rivers and the lake. Lake Taihu is located in the center of the basin, which is characterized by a complex network of rivers and channels. To assess the sources and fate of dissolved organic matter (DOM) in surface waters, we determined the components and abundance of chromophoric dissolved organic matter (CDOM) within Lake Taihu and 66 of its tributaries, and 22 sites along transects from two main rivers. In Lake Taihu, there was a relative less spatial variation in CDOM absorption a CDOM(355) with a mean of 2.46±0.69m−1compared to the mean of 3.36±1.77m−1 in the rivers. Two autochthonous tryptophan-like components (C1 and C5), two humic-like components (C2 and C3), and one autochthonous tyrosine-like component (C4) were identified using the parallel factor analysis (PARAFAC) model. The C2 and C3 had a direct relationship with a CDOM(355), dissolved organic carbon (DOC), and chemical oxygen demand (COD). The separation of lake samples from river samples, on both axes of the Principal Component Analysis (PCA), showed the difference in DOM fluorophores between these various environments. Components C1 and C5 concurrently showed positive factor 1 loadings, while C4 was close to the negative factor 1 axis. Components C2 and C3 showed positive second factor loadings. The major contribution of autochthonous tryptophan-like components to lake samples is due to the autochthonous production of CDOM in the lake ecosystems. The results also showed that the differences in geology and associated land use control CDOM dynamics, such as the high levels of CDOM with terrestrial characteristics in the northwestern upstream rivers and low levels of CDOM with increased microbial characteristics in the southwestern upstream rivers. Most of river samples from the downstream regions in the eastern and southeastern plains had a similar relative abundance of humic-like fluorescence, with less of the tryptophan-like and more of the tyrosine-like contributions than did samples from upstream regions. [Copyright &y& Elsevier]