Competitive interactions are a central force maintaining local diversity and controlling the structure of plant communities. Several investigations indicate that the outcome of plant competition can be influenced by biotic and abiotic factors. However, such studies usually evaluate single factors. Since biotic and abiotic factors affect plant competition at the same time, it is important to understand the nature of their inter-relationships. In this work I assessed the effects of ultraviolet (UV) radiation and mycorrhizal colonization on plant competition. The results showed that UV radiation induced changes in leaf morphology and biomass allocation. The results also showed that UV radiation diminish the rate of mycorrhizal colonization. However, neither AM colonization nor UV radiation affected the outcome of plant competition. These results indicated that the high degree of total competitive stress masked the effects of the UV radiation stress and AM colonization on plant growth. The findings here should be especially useful to professionals interested in the study of plant interactions.