2.2 Experimental set-up
The experiment was set up in the National Field Station of Liangzi Lake Ecosystem of Wuhan University, Hubei Province, China (N 30°05’–30°18’, E 114°21’–114°39’). The mesocosm system was made up by 32 plastic tubs (60 cm in diameter and 65 cm in height). Each tub was filled with 15-cm-thick sediment collected from the bottom of Liangzi Lake. The lake sediment was sieved to remove aquatic plants and propagules, then mixed evenly before the experiment set-up. Then, Liangzi Lake water was carefully and fully added into each tub. The unwarming treatment or the control (CK) was established by placing 16 mesocosms in an outdoor platform (10 m L × 10 m W). A 3-meter-high transparent rainproof roof was set up above unwarming mesocosms to prevent disturbance from rainfall (Wang et al., 2021a). The warming treatment was mimicked by placing the remaining 16 mesocosms in a glasshouse (Liu et al., 2016; Yan et al., 2021). Four selected germinated turions were respectively planted into the center of the sediment of four unwarming and warming mesocosms. Thus, each treatment of geographic source and warming was replicated four times. The experiment started on January 22nd, 2014. During the experiment, each mesocosm was checked every three days. The algae and snails on the plant body were carefully removed to prevent the disturbance to the growth of P. crispus from these organisms. Each mesocosm was also confirmed to be full-filled with lake water by adding lake water throughout the experimental period. The day water temperature of each mesocosm was measured every five days using the YSI Professional Plus water quality probe (YSI Co, OH, USA) at 8:00, 12:00 and 18:00. The mean water temperature in the glasshouse was 2–5.8 ℃ higher than that outdoor (Fig. 2).