Abstract: Population characteristics and interspecies relationships are important in the study of population ecology. To investigate the environmental plasticity mechanisms of Agropyron mongolicum populations, three 10 m×10 m plots dominated by communities of Stipa breviflora+A. mongolicum, A. mongolicum+Lespedeza potaninii and A. mongolicum+Cynanchum komarovii were studied in desert steppe grassland in Yanchi County. The spatial coordinates and quantitative characteristics, including height and above ground biomass of A. mongolicum were measured in the study plots. The spatial distribution pattern of the A. mongolicum populations and the interspecific relationships between the A. mongolicum populations and other dominant species in the studied plant communities were analyzed by ‘point pattern analysis’ and ‘O-ring function statistic’ methods. It was found that the density, ground cover and above-ground biomass of A. mongolicum populations in A. mongolicum+L. potaninii communities were significantly higher than those in S. breviflora+A. mongolicum and A. mongolicum+C. komarovii communities (P<0.05), and the height did not differ significantly among the three communities (P<0.05). The spatial pattern of A. mongolicum populations mainly displayed an aggregated distribution, with an aggregation scale of less than 4 m. When spatial distribution was evaluated at larger scale, the aggregation degree decreased with increasing scale and gradually transformed to random and uniform distribution. The associations between A. mongolicum and S. breviflora populations, and A. mongolicum and L. potaninii populations showed a negative relationship at a scale of less than 4 m and tended to show no association with increase in the evaluation scale. No association between A. mongolicum and C. komarovii populations was detected at the 0-5 m evaluation scale.

Key words: desert steppe, Agropyron mongolicum, spatial distribution pattern, interspecific relationship, point pattern analysis