Pot experiments were used to simulate the heterogeneity and homogeneity of forest soil environment in order to explore the differences in productivity of mixed and pure forests of Schima superba. In addition, three kinds of planting patterns were established, including the single planting, double pure planting, and mixed planting with Chinese fir, for evaluating the effects of competition from neighboring plants on dry matter accumulation, and nitrogen and phosphorus efficiency of three provenances (Jian'ou of Fujian, Xinfeng of Jiangxi, and Longquan of Zhejiang) of S. superba in heterogeneous nutrient environments. The results showed that all the three provenances had high dry mass, and nitrogen and phosphorus absorption efficiency in heterogeneous nutrient environments, particularly in Jian'ou provenance. The effect of competition with neighboring plants on growth, and nitrogen and phosphorus absorption efficiency in three provenances was significant. In the presence of competition from Chinese fir (i.e., in the mixed plantation treatment), the dry matter content in Jian'ou provenance of Fujian was higher than that in the single planting and double pure planting treatments. Dry matter content was related to its root:shoot ratio and physiological plasticity. In the mixed planting treatment, the root:shoot ratio decreased significantly, and more dry matter was distributed in the leaves, thereby enhancing the photosynthetic capacity. Meanwhile, the enhanced nitrogen and phosphorus absorption efficiency improved dry matter quality to enhance competitiveness. However, the nitrogen and phosphorus absorption efficiency of Xinfeng and Longquan provenances in the mixed planting treatment were either inferior or similar to that in single planting, but with higher root:shoot ratio, which affected dry matter accumulation. Intraspecific competition inhibited the nitrogen and phosphorous utilization efficiency, but enhanced their uptake in Longquan and Xinfeng provenances. However, nitrogen and phosphorous uptake in the Jian'ou provenance was little affected by intraspecific competition. it was significantly higher than that in the other provenances, thereby enhancing the dry matter content. The results suggested that the higher biomass allocation and physiological plasticity in the Jian'ou provenance were the main reasons for its high productivity and competitive advantage.