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).