Effects Of Positive Interactions On Individual Plant Miniaturization And Population Spatial Patterns Under Grazing Stress Among Plants

The investigation of interactions among plants has been a focus of ecology during last decades. Many studies in last20years have demonstrated that positive interaction may act simultaneously with competitive interaction in a community, and the over effect of interactions depends on which mechanism is the most important in a given environment. The temperate steppe of China has been heavily disturbed by overgrazing, which has resulted in serious degradation and characteristic vegetation patterns. The degraded community exhibited individual plant miniaturization. Miniaturized display show the following characteristics: shortened internodes, contracted leaf blades and a shallowly distributed root system. However, the mechanism of individual plant miniaturization has not been unlocked. Thus, Can the shift from facilitation to competition occur along gradients of grazing stress? In other words, can we incorporate the mechanisms of degradation in steppe into mainstream ecological theories based on the balance of facilitation and competition? A considerable challenge in plant ecology is to understand how interactions, such as competition or facilitation, shape the spatial distribution of plants. If facilitation and competition are balanced along gradients of grazing pressure, how does the balance between facilitation and competition affect spatial patterns? Choosing different restored successional communities in typical steppe and by combining field experiments and statistical models, the dissertation explores the effects of positive interactions on individual plant miniaturization and population spatial patterns under grazing stress among plants, and attempt to unlock mechanisms of degradation or miniaturization based on the theoretical framework of the balance of facilitation and competition. Using test statistics based on the univariate O-ring statistic to describe local density at different scales in different restored successional communities, the results show that facilitation is the dominant interaction in a seriously degraded community, and demonstrate that the shift from facilitation to competition along gradients of grazing stress are due to intraspecific interactions.Facilitation is the dominant interaction in a seriously degraded community. Under facilitation the plant populations defense strong grazing pressure by changing their morphology and distribution. The positive interaction theory can detect the mechanism of individual plant miniaturization, which further illustrate individual plant miniaturization is caused by facilitation in a seriously degraded community.Along gradients of grazing stress the shift of intraspecific interactions from facilitation to competition. By using point pattern analysis with different null models to detect the population spatial patterns in different restored successional communities, the results show the shift from facilitation to competition determine the spatial patterns in plant populations, which is caused by variation in small local density depending on the balance between facilitation and competition. Thus the mechanisms of degradation in typical steppe are incorporated into mainstream ecological theories based on the balance of facilitation and competition.In all, in a seriously degraded community positive interaction is the dominant interaction, and by facilitation theory we scientifically explain the mechanisms of individual plant miniaturization. This is valuable for us to cognize the degradation and restoration on the typical steppe.