Surface Shading, Soil Temperature, and Soil Moisture Effects on C Loss in a Temperate Peatland

Abstract

TAGGART, MATTHEW. Surface Shading, Soil Temperature, and Soil Moisture Effects on Soil C Loss in a Temperate Peatland. (Under the direction of Joshua Heitman). Histosols are a huge reservoir for C, covering < 1% of the world‟s land surface but holding up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from peatlands is critical for proper management of these C sinks. Three experiments evaluated how formerly cultivated, warm climate Histosols undergoing restoration efforts might respond to increasing water content via water table re-establishment and decreases in soil temperatures via vegetative shading. We compared temperature and soil CO2 efflux differences from intact soil cores, collected from Juniper bay, 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 at Juniper bay 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. Vegetation 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. C mineralization response to temperature and moisture was verified with lab incubations of soil material at 25° and 37°C for three moisture ranges. Incubation showed a temperature/moisture interaction where Q10 was 2.55 under wet soil conditions (0.40 m3 m-3) and 1.64 when soil was driest (0.15-0.16 m3 m-3). All results confirm surface shading has a strong influence on soil temperatures and C mineralization rates. Thoughtful management of vegetation in mitigated peatlands may be an effective strategy for slowing soil C losses and promoting soil C sequestration.