Soil respiration under different soil moisture conditions in a temperate forest in Maryland, USA
Soil respiration, including both autotrophic and heterotrophic respiration, represents a large portion of carbon flux between terrestrial ecosystems and the atmosphere. Given the large pool size of soil carbon and high flux, soil respiration could potentially be an important factor influencing atmospheric CO2 levels. Soil moisture, which is influenced by precipitation, is a major driver of soil respiration. Precipitation patterns, including annual amounts, timing, variability and extremity are expected to change in the future globally. Rainout shelters are commonly used for studying ecosystem responses to altered wetting-drying cycles. Smaller shelters are open to criticism due to edge effect. We built rainout shelters at the Smithsonian Environmental Research Center (SERC), Maryland to understand how forest soils respond to precipitation extremes. First, we wanted to determine whether we could create and sustain dry soil conditions on a small scale in a wet temperate forest. Furthermore, we measured weekly soil respiration data in two additional plots: one was regularly irrigated while the other was not.
Rain exclusion shelters had significantly lower soil moisture than background, indicating that we created persistent dry conditions on a small scale in a forest. The irrigated site had a consistently higher flux of CO2 than non-irrigated site. Soil respiration, ranging from 97.3 to 190.1 and 165.9 to 298.7 mg CO2 m-2h-1 for non-irrigated and irrigated sites, peaked at mid July and decreased gradually from August to October. Soil temperature and moisture jointly drive soil respiration: the former drives the trend while the latter is responsible for the difference between the two plots. These manipulations will be used to define the relationship between meteorology and soil carbon fluxes for forest stands of different land use histories and to parameterize process-based soil carbon routines within the widely used Community Land Model.