Plant litter is an important component in wetland ecosystems, and the role of plant litter decomposition is considered to be important for wetland ecosystem functions and services. However, the consequences of litter inputs have seldom been experimentally tested in real ecosystems such as constructed wetlands (CWs). The enriched nutrients in CWs might weaken the role of litter inputs on soil carbon and nitrogen cycling. Here, we conducted a two-month field experiment to examine the effects of litter inputs on the soils in CWs. Our results showed that litter inputs significantly affected soil microbial (bacterial and fungi) diversities and properties (soil total nitrogen and nitrogen isotopes), and litter species with higher stoichiometry ratios, i.e. C/N, C/P and N/P led to higher microbial diversities. However, litter species had no or weak effects on microbial activities (CO2 and CH4 flux) or on the relative abundance of microbial communities, indicating that other environmental factors in such a CW might have stronger effects on those factors than litter inputs. These results highlighted the importance of submerged plant litter in nutrient-rich wetland ecosystems and provide potential tools for managers to improve the ecosystem functions and/or services via altering microbial diversities.