Research area
The Yili Valley (42°14′–44°53′N, 80°09′–84°56′E) lies in the westernmost part of the Tianshan Mountain Range in the Xinjiang Autonomous Region. The region has an average annual temperature and precipitation of 10.4°C and 417.6 mm, respectively. Yili Valley can be thought of as a wet island in the arid area of Xinjiang, as it has an abundant and unique set of plant species, and the valley is listed as one of five most important areas of terrestrial biodiversity in China (Chen, 1993).
Xinyuan County (43°03′–43°40′N, 82°28′–84°56′E) is located in the hinterland of the Gongnaisi grassland in the eastern part of the Yili Valley. This site is the main distribution area of A. artemisiifolia and A. trifida. The average annual temperature and precipitation are 8.1°C and 480 mm, respectively. We studied the interspecific competitive ability, seed size, and water demand differences between the two species in farmland ecotone, residential area, roadside, and grassland in Xinyuan County, because these four habitats were the main distribution areas of the two species (Dong et al., 2017), and there were relatively large differences in water status, temperature status, and companion species between those four habitats.