Abstract: Interspecific relationship is a characteristic of community succession, which is often represented by interspecific association. In this study, variance ratio method was used to calculate the overall association of the main plant species. Based on χ²test, association coefficient, percentage of co-occurrence, Ochiai index, and Dice index, the temporal stability and species asynchrony of plant community were calculated. The interspecific association of seven main species in a Stipa breviflora desert steppe was studied under no grazing and heavy grazing to understand the effects of heavy grazing on the interspecific relationship and community stability. The results showed that: (1) Under no grazing, the overall association was non-significant negative association among the main species. The proportion of negative association pairs (33.3%) was the largest. Under heavy grazing, however, the overall association was significant positive association. The proportion of positive association pairs (57.1%) was the highest. Heavy grazing changed the relationship of main species from competition to mutual facilitation. (2) Co-occurrence percentage, Ochiai index, and Dice index were all decreased under heavy grazing, indicating that the relationship between the main species was looser under heavy grazing than under no grazing. (3) The temporal stability and species asynchrony of the community under heavy grazing areas decreased, indicating that plant community was in a relatively unstable state with heavy grazing. The effects of heavy grazing on community stability were closely related to the change of interspecific relationship. The closer the interspecific relationship was, the more stable the community was.

Key words: Ommastrephes bartramii, statolith, trace element, Northwest Pacific Ocean.