Shift in plant-soil interactions along a lakeshore hydrological gradient.

Wetlands occupy the transitional zone between aquatic and terrestrial systems. Hydrological conditions have significant influence on wetland plant communities and soil biogeochemistry. However, our knowledge about plant-soil interactions in wetlands along hydrological gradients is still limited, although it is crucial to guide wetland management decisions and to adapt, whenever possible, hydrological conditions to the different plant communities. To this aim, we related vegetation composition, plant functional traits, soil physicochemical properties, soil microbial biomass, and soil enzymatic activities in wetlands on the southeastern shore of Neuchâtel lake, Switzerland, a lake whose level is partly regulated. Aboveground and belowground plant biomass and correspondent C, N and P concentrations remained constant or decreased moving from the vegetation community subjected to more frequent flooding events to the community with almost no flooding. The soil organic layer exhibited always higher nutrient concentrations and greater enzymatic activities than the organo-mineral and mineral layers. The chemical and biological characteristics of the soil organic layer showed decreasing values for most of the parameters along the hydrological gradient from lakeshore to upland wetland communities. On the basis of nutrient stoichiometry, plant-soil system in the plant community with most flooding events had no-nutrient limitation, while there was a N limitation in the transitional community. In the upland plant community where there was no flooding effect, the plant-soil system was characterized by N and P co-limitation. These findings are important because they provide a threshold for flooding regime by the lake in the context of optimization of lake level regulation under various stakeholders needs.