Small-scale constructed urban roadside biotopes are increasingly implemented as components of urban green infrastructure; however, relationships among aboveground net primary productivity (ANPP), plant species richness, and environmental conditions in these habitats remain poorly understood. This study examined the relationships among ANPP, native and alien species richness, and environmental factors in constructed urban roadside biotopes. We conducted vegetation surveys, biomass sampling, and measurements of light and soil conditions across 67 roadside biotope sites to assess relationships among ANPP, species richness, and local environmental conditions. ANPP was positively associated with native species richness, whereas no significant relationship was detected between ANPP and alien species richness. ANPP and native species richness both increased with light availability and decreased with higher soil electrical conductivity (EC), while ANPP also declined with increasing soil moisture. In contrast, alien species richness showed no consistent relationship with ANPP or the main environmental variables. Canonical correspondence analysis broadly corroborated the regression results, indicating that native species were associated with higher light availability and greater productivity of the biotope, whereas alien species were more closely associated with higher soil moisture and higher soil EC. These results suggest that ANPP, native species richness, and species composition in small-scale constructed urban roadside biotopes vary along local environmental gradients, particularly light availability, soil EC, and soil moisture. Accordingly, the design and management of roadside biotopes should consider securing sufficient light and minimizing soil EC accumulation and excessive soil moisture to enhance ANPP and native species richness in small-scale urban green infrastructure.