Aim: Coastal wetlands provide critical ecosystem functions and services, e.g. coastal protection, nutrient retention and C sequestration. Despite the important roles in global C, N and P cycling, the global variation in leaf stoichiometry across coastal wetlands remains unclear.

Location: Global.

Time period: 1980-2018.

Major taxa studied: Vascular plants.

Methods: By compiling a global dataset of 698 data records in 205 sites, we systematically analysed the world-wide trends and their determinants in leaf element contents and ratios of plants across coastal wetlands.

Results: Leaf N and P contents significantly increased, but C:N, C:P and N:P ratios decreased with increasing latitude in coastal wetlands. Mean annual temperature was the predominant driver of leaf N, P and C:N, while soil N:P was a good predict of leaf C:P and N:P ratios. Furthermore, N increased faster with P in plant leaves of coastal wetlands compared to terrestrial ecosystems. Within coastal wetlands, herb-dominated salt marshes had significantly higher leaf P content, lower leaf N:P ratio and lower scaling exponent of leaf N to P than tree-dominated mangroves.

Main conclusions: The similar latitudinal patterns of leaf stoichiometry in coastal wetlands as terrestrial ecosystems reflected the similar influences of temperature. However, different slopes of leaf P and N:P ratios and N and P scaling relationships between these two ecosystems suggested that different salinity and tidal inundation levels result in different N and P use strategies in coastal wetland plants. These differences in leaf stoichiometry between ecosystems and between different types of coastal wetlands may need to be emphasized in future biogeochemical modelling due to their different roles in global nutrient and carbon cycling.