Soil physical and chemical properties
The differences in soil physical and chemical properties were compared between farmland ecotones, residential areas, grasslands, and roadsides. The upper 0–20 cm of soil from four habitats (selected at observation points determined in 2010 in Experiment 1 where A. artemisiifoliaand A. trifida were present) was divided into two layers. The soil in each 10-cm layer was sampled, and soil properties were determined in July 2017 as follows. Total nitrogen, total phosphorus, and total potassium were determined using the micro-Kjeldahl, sodium hydroxide melting-molybdenum anti-colorimetric, and flame photometry methods, respectively. Soil pH was measured using a Mettler-Toledo pH meter (UB-10, USA), and soil conductivity was measured using a conductivity meter (Hach, USA). Soil organic matter content was checked using the K2CrO7-H2SO4external heating method. Alkaline hydrolysis nitrogen, available P, and available K were measured using the alkaline hydrolysis diffusion method, Mo-Sb colorimetry, and the ammonium acetate method, respectively. Soil samples from each habitat were taken three times in three individual sites (more than 5 km apart), and a total of 3 (repetition) × 4 (habitat) × 2 (soil layer), which resulted in 24 samples being collected.