ALBERT

Description: Understanding how the salt marsh vegetation will evolve under future climate conditions is essential for predicting the role of marsh ecosystem services in a warmer climate with higher CO 2 -concentrations. In a mesocosm experiment in the northern Wadden Sea, the impact of increased temperature (+ 3 °C) and CO 2 (800 ppm) on salt marsh vegetation was investigated, assessing biomass production in the pioneer zone and low marsh. The pioneer zone, which was dominated by Spartina anglica and exposed to natural tidal inundations , demonstrated a differentiated response between belowground and aboveground biomass. Aboveground biomass increased in response to enhanced CO 2 availability, and belowground biomass increased in response to raised temperatures. Other plant species accounted for less than 18% of the aboveground biomass, and their biomass was suppressed under high CO 2 availability. Increased biomass by Spartina anglica may improve resilience toward sea level rise. Hence, the pioneer zone is expected to maintain its coastal protection and blue carbon storage capacity under future climate conditions. The low marsh, which was dominated by Elymus athericus , was exposed to higher than usual tidal inundations and resembled a scenario with increased sea level. The low marsh showed no response in biomass to increased CO 2 or temperature, which may be due to the increased flooding. The positive response of Spartina anglica (C 4 plant) and the lack of response in Elymus athericus (C 3 plant) counter the notion that C 3 plants are more productive under future climate conditions and demonstrate that C 4 plants can also thrive in future salt marshes.