Soil texture and pH affect soil CO2 efflux in hardwood floodplain forests of the lower middle Elbe River

Floodplain ecosystems play a significant role in the global carbon (C) cycle, particularly due to their C sink potential in hardwood floodplain forests. However, in these forests, interactions between a heterogeneous micro-relief and anthropogenic landscape changes make estimating C loss through soil CO2 efflux difficult. To determine the drivers of soil CO2 efflux, we selected six hardwood floodplain forests at the lower middle Elbe River, which were distributed among different relief positions (low-lying or high-elevated) in the active and former flooding zone. We measured soil CO2 effluxes over a full year using the closed-chamber method. Based on the response of soil CO2 efflux to soil moisture and temperature, annual efflux rates were determined, which were then related to soil properties, such as pH, texture, soil organic carbon (SOC) and nitrogen (N) content. Soil CO2 efflux ranged between 1006 (& PLUSMN;99) and 2214 (& PLUSMN;118) gC m(-2) year(-1). Maximum efflux occurred in a former floodplain forest that was disconnected from Elbe River water table fluctuations. SOC-specific soil CO2 efflux (gC gSOC(-1) year(-1)) was smallest in low-lying forests of the active flooding zone and reflected by the appearance of redoximorphic mottling close to the soil surface. Fine texture (< 6.3 mu m), SOC and N were related positively and electric conductivity, C/N and pH negatively to total soil CO2 efflux. Soil pH and fine texture were the strongest univariate predictors for total soil CO2 efflux (both R-2 = 0.59). Fine texture, pH and C/N ratio explained 66% of the variance in total soil CO2 efflux according to multiple linear regression. We conclude that, in hardwood floodplain forests, soil CO2 efflux is mainly controlled by fine texture and soil pH. Fine texture can be related to soil moisture and nutrient availability and may have a positive effect on the activity of microorganisms.