Study site
The study was conducted in a wild population of V. negundo var.heterophylla (30 × 30 m, population density of 5.3 plants per
100m2) in Qiangu Mountain (36°49′ N, 120°73′ E,
210-220 m above sea level) in Qingdao, Shandong Province, China. The
study area belongs to the warm temperate monsoon continental climate,
and also has significant maritime climate characteristics, which is
characterized by humid air, abundant rainfall, moderate temperature, and
four distinct seasons. The hottest month is August, with an average
temperature of 25.3 ℃; the coldest month is January, with an average
temperature of minus 0.5 ℃. The average annual temperature is about 12
℃, and an average annual rainfall of about 662 mm. According to our
measurements, the soil pH was 5.3, and the content of total nitrogen,
total phosphorus, and organic matter in soil during the summer were 0.15
(g/kg), 0.24 (g/kg), and 50.8 (g/kg), respectively. In our study sites,V. negundo var. heterophylla was identified as the
dominant species (1-20 cm in diameter) in the study area, and the
subdominant species was Ziziphus jujuba var. spinosa(Rhamnaceae).