2.1. Study area
The experiment was conducted on riparian slopes of the lower Yellow River, Zhongmu County, Henan Province, China (Fig. 1a, b), from September to October 2015. Zhongmu County is located at the south bank of the Yellow River (N 34°26′–34°56′, E 113°46′–114°12′) with a total area of 1406 km2. The climate in Zhongmu County is a typical warm temperate continental monsoon climate, characterized by mild windy springs (April–June), hot rainy summers (July–September), and cool dry autumns and winters (October–March). The mean annual temperature is 14.2ºC, and the maximum and minimum monthly temperatures occur in July and January respectively (Geng et al., 2012; Zhao et al., 2016; Zhao et al., 2015b). The mean annual precipitation is 616 mm, with significant seasonality; most precipitation occurs during the rainy season (Geng et al., 2012; Zhao et al., 2016; Zhao et al., 2015b). Influenced by historical floods of the Yellow River, sedimentary rocks in Zhongmu County are mainly alluvium and diluvium, and soils contain much sub-sand and silt-sand (Zhao et al., 2015b). Vegetation in Zhongmu County is limited by the climatic characteristics and soil and water conditions. The dominant plant species in this area include Salix babylonica ,Populus L. , and grass (Setaria viridis ). The families Gramineae, Compositae, Leguminosae, and Brassicaceae occupy an important position in the lower Yellow River riparian flora. While the main agricultural crops in this area are wheat (Triticum aestivum L. ) and maize (Zea mays L. ) (Zhao et al., 2015b).
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