It is of great significance to compare exotic plants with their respective indigenous plants in growth and effect on soil properties for studies on mechanism of their successful invasion. Subtropical and tropical soils are often strongly weathered and hence low in phosphorus availability. Why can invasive plants, such as Wedelia trilobata, successfully invade South China, where the soil is deficient in phosphorus? An answer to this problem is of great significance for exploration of mechanism of the invasive plants flourishing in infertile soils. However, so far few reports on this topic have been found in the literature. This paper laid its focuses on soil organic phosphorus mineralization, and activities of acid phosphomonoesterase and alkaline phosphomonoesterase in the soils under W. trilobata, native plant W. chinensis and their hybrid in South China. A controlled field experiment using randomized complete block design was laid out in July 2016. The plots in the experiment were planted with W. trilobata, native plant W. chinensis and their hybrid, separately for comparison between the plots in microbial biomass phosphorus, activity of acid and alkaline phosphomonoesterase and soil organic phosphorus mineralization, and for analysis of underlying mechanisms of any possible differences. Results show that Treatment WT (W. trilobata) was higher than Treatment WC (W. chinensis) in soil dissolved organic carbon. In all the three treatments Labile-P accounted only for 2.2%~6.3% of the soil total phosphorus. Treatment WT and Treatment H (hybrid) was higher than Treatment WC in Labile-P, but lower in organic phosphorus, residual phosphorus, total phosphorus and microbial biomass phosphorus. Microbial biomass phosphorus made up 14.3%, 41.2% and 25.7% of the total phosphorus in Treatments WT, WC and H, respectively. The ratio of soil total carbon to organic phosphorus reached well beyond 200, indicating that soil phosphorus was a major limiting factor in the studied region. Soil organic phosphorus, as an important fraction in soil total phosphorus, accounted for 28.7%, 17.6% and 25.0% of the total phosphorus in Treatments WT, WC and H. Correlation analysis shows that Labile-P was significantly and positively related to alkaline phosphomonoesterase, but negatively to alkaline phosphomonoesterase. Treatments WT and H were higher than Treatment WC in activity of alkaline phosphomonoesterase, but did not differ much in activity of acid phosphomonoesterase. So, changes in organic phosphorus fractions were mainly driven by alkaline phosphomonoesterase. The findings suggest that both the invasive and native plants suffer from phosphorus deficiency, and alkaline phosphomonoesterase decomposing soil organic phosphorus may be the major mechanism of the invasive plants adapting to phosphorus limitation in the region. It is expected that this study may help understand the general rule of plant invasion in habitats poor in resource from the new perspective of soil organic phosphorus mineralization.