The intricate interplay among plant productivity and soil factors is a pivotal driver for sustaining the carbon sequestration capacity of coastal wetlands. Yet, it remains uncertain whether climate warming will reshape the cause-and-effect interactions between coastal plant productivity and soil factors. In this study, we combined a manipulative warming experiment with a convergent cross-mapping technique to quantify the causal relationships, which can be either unidirectional or bidirectional, between plants (gross primary productivity, GPP) and soil environment (e.g. soil temperature, moisture and salinity). Our findings revealed that warming amplified the interaction between GPP and soil salinity in the coastal wetland ecosystem. While soil temperature primarily drove this causal relationship in control plots, a more complex interaction emerged in warming plots: soil salinity not only directly influenced GPP but also indirectly affected it by altering soil temperature and moisture. Overall, warming increased the number of causal pathways linking GPP with soil environmental factors, such as the effect of soil salinity on GPP and the impacts of GPP on soil moisture. These findings provide experimental evidence of intensified plant–soil causality in coastal wetlands under climate warming.