Intra- and interspecific competition and modifications in environmental characteristics are the main drivers of plant community dynamics, but few studies have investigated the combined effects of competition and phosphorus (P) availability on ecological succession. Seedlings of conifers Abies fabri and Picea brachytyla were collected from the late-stage Hailuogou glacier retreat area and grown under different P regimes (control and P fertilization) to investigate the impact of intra- and interspecific competition on photosynthetic capacity, resource (water, N and P) use efficiency and growth performance in two types of native soil. In the control treatment, there were no differences in the total biomass of A. fabri between the two competition patterns under either type of soil, whereas interspecific competition decreased the total biomass of P. brachytyla grown in the soil collected from A. fabri plots. However, under P fertilization, A. fabri individuals exposed to interspecific competition showed a stronger competitive ability, as their total biomass, absolute height growth rate, net photosynthetic rate, water use efficiency (delta C-13) and leaf P content were significantly higher under interspecific competition compared to intraspecific competition. No differences in these traits were detected in P. brachytyla between the two competition patterns. The results indicated that P plays an important role in determining asymmetric competition patterns among Pinaceae species. The interactive effect of interspecific competition and P availability highlighted here could influence the community composition and dynamics of plants during late stage primary succession in a glacier retreat area.