Surface shading effects on soil C loss in a temperate muck soil

Histosols are a huge reservoir for C, covering < 1% of the world's land surface but storing up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from Histosols is critical for proper management of these C sinks. Two experiments evaluated how formerly cultivated, warm-climate Histosols undergoing wetland restoration respond to decreases in soil temperatures via vegetative shading, under different water table conditions. We compared temperature and soil CO2 efflux differences from intact soil cores under three levels of light reduction in a greenhouse: 0%, 70%, and 90%. Soil in full sun was consistently warmer and showed higher efflux rates than 70% and 90% shade treatments: 4.132, 3.438, and 2.054 μmol CO2 m−2 s−1, respectively. Shade treatments reached peak efflux rates at similar water potential, −2 to − 4 kPa. A field experiment subjected in-situ soil to full sun, 70% light reduction, and light reduction from naturally occurring herbaceous vegetation. Shade treatment effects on soil temperature and C mineralization were evident throughout the growing season. Vegetative shade effects on soil temperature were greatest in August and September when soil under vegetation was 5–11 °C cooler than unshaded soil. Soil CO2 efflux was correlated strongly with soil temperature; daily efflux rates were consistently highest from unshaded soil. Efflux across treatments showed a strong seasonal correlation to soil moisture, increasing as soil dried in response to water table decline. Soil water potential was unaffected by shade treatment, suggesting temperature effects were solely responsible for efflux differences between treatments. All results confirm that surface shading has a strong influence on soil temperatures and C mineralization rates. Management to enhance vegetative shading in wetland restoration projects may be an effective strategy for slowing soil C losses and promoting soil C sequestration when O2 is not limiting.

Research highlights
► Two experiments evaluated how formerly cultivated, warm-climate Histosols respond to decreases in soil temperatures via vegetative shading, under different water table conditions.
► Results confirm that surface shading has a strong influence on soil temperatures and C mineralization rates.
► Findings suggest that management to enhance vegetative shading in wetland restoration projects may be an effective strategy for slowing soil C losses and promoting soil C sequestration when O2 is not limiting.