Analysis of the effects of different restoration approaches on the structure and functioning of salt marshes in the Venice lagoon

Salt marshes are coastal ecosystems that provide key services to human population, such as coastal protection and blue carbon sink. Marshes have strongly deteriorated in past decades and, thus, countries worldwide invested in marsh restoration programs, mainly aiming at recreating species structural. However, if we want to correctly evaluate the success of a restoration both structural and functional aspects must taken into account. To evaluate restoration success, plants functional traits provide a powerful approach because they allow to link if changes in community species composition are reflected at functional level and, in turn, if they impact on the functioning of the systems. Here, focusing on extensive salt marsh restorations undertaken in the Venice lagoon, we investigated if two different restoration approaches - one involving the partial removal of structures for protecting the edges (R1), while no removal was done in the other (R2) - recreated similar taxonomic and functional vegetation composition to natural marshes. In turn, we investigated if changes in functional composition affected the above- and belowground primary production. Our results revealed that restored marshes lacked key vegetation in the low shore (i.e., the native Sporobolus maritimus was not present in both type of restored marshes). Furthermore, in the mid marsh, vegetation communities of restored marshes differed from natural ones, both in taxonomical composition and in functional traits. Yet, despite based on functional traits we expected production in R2, we did not find statistical differences in both above- and belowground primary production between natural and restored marshes Overall, our study found that different type of restorations can have enduring effects on the structure and vegetation functional traits, but not on the functioning of salt marsh ecosystem. Further research on the complex relationships between functional traits, restoration and ecosystem functioning are needed.