Microbial activities in soils of a healthy and a declining reed stand

Microbial processes were investigated in the soil of a declining, more eutrophic (Rozmberk West) and a healthy looking, less eutrophic (Rozmberk East) freshwater reed stand. Soil was sampled monthly from June to September 1997. Glucose induced carbon dioxide (CO2) production in oxic and anoxic conditions, methane (CH4) production, nitrification and denitrification activities were measured in laboratory conditions in suspensions prepared from homogenised soil samples. Within a stand the proportion of anaerobic (as opposed to aerobic) microbial activity was greatest in June. Potential methanogenesis was highest in June and decreased later in both stands. Methane production was approximately the same in June at both stands but it was higher at Rozmberk East than at Rozmberk West stand in later months. Denitrifying activity was higher in August than July at both stands. Nitrifying activity was undetectable at both stands over the entire study period. Generally Rozmberk West was more anaerobic than Rozmberk East, with lower redox potential, higher amounts of oxygen-consuming organic matter and a lower ratio of CO2 production in oxic conditions to CO2 production in anoxic conditions. Microbial activity was apparently restricted at Rozmberk West stand in comparison to Rozmberk East. The shift from aerobic to anaerobic microbial metabolism and a coinciding restriction of metabolic activities at Rozmberk West are thought to be indicative of a strengthened oxygen stress in the soil, associated with accumulation of metabolites toxic to both the microorganisms and the reed. Possible links between eutrophication, microbial characteristics and reed performance are discussed.