Habitats where plants grow, not only directly affects the resource availability and allocation, but also indirectly affects the plants' reproductive status by shaping the community, especially the composition and behavior of pollinators. The direction and relative strength of direct and indirect effects are rarely considered simultaneously, which limits our understanding of environment-driven differences in plant reproduction. We placed Sagittaria trifolia plants of the same genotype composition in two common gardens that differed considerably in light (understory and sun). During the peak of anthesis, we quantified the flowering status, identified visiting insects, and recorded their foraging behaviors. The reproductive output of plants in both habitats was also estimated in aspects of fruit-set as well as seed number and size. The results showed that plants in the sun had more flowers and flowering individuals than those in the understory did. The main visitors of S. trifolia could be summarized into four categories, namely the hoverfly, bee, butterfly, and fly, among which, the hoverfly and bee were the most important in the understory and sunlit habitats. The pollinator visitation frequency was higher in the sun than it was in the understory. During each foraging bout, a higher number of male flowers, total flowers, and inflorescences in the sun were visited than those in the understory. The S. trifolia plants grown in the sun had a higher fruit-set than those grown in the understory, but there was little variation in their seed per fruit and seed size. Taken together, these results indicate that the total reproductive output of plants grown under the two habitats showed more than three-fold differences, which was caused by accumulation in the same direction induced by direct and indirect environmental effects, and the former appeared to be the dominating factor. Our study highlights the importance of focusing on the interactions between plants and the physical environment as well as biotic factors at every step of plant reproduction, especially the distinctive performances of pollinators.