Response of biogeochemical processes of the water-soil-plant system to experimental flooding-drying conditions in a eutrophic wetland: the role of Phragmites australis

Assess the role of Phragmites australis in the temporal variability of physico-chemical and microbiological soil properties related to biogeochemical processes in eutrophic wetlands. A mesocosms experiment was performed with alternating flooding-drying conditions with eutrophic water at two nutrient levels, and soil Eh, pH, temperature, CO2 emissions, dissolved organic carbon, carbon from microbial biomass, and Phragmites physiological activity were measured during 44 weeks. In surface, Eh decreased with flooding and increased with drying regardless plant presence and nutrients content. In depth, Phragmites maintained oxic conditions. During warmer months, O-2 diffusion promoted by Phragmites hindered the drop of pH. Soil microbial respiration was stimulated in warmer months (soil temperature similar to 20-30 A degrees C), as shown by larger CO2 production, and higher aromaticity and phenolic compounds content in pore water. The latter occurred regardless the plant presence and nutrients content, although the combination of both contributed to a higher microbial population (shown by higher concentrations of carbon from microbial biomass). The presence of Phragmites and the nutrient concentration in the flooding water had a different role in the temporal evolution of the physico-chemical and microbiological soil properties in eutrophic wetlands, and this role was strongly influenced by soil depth and temperature.