How will coastal forests respond to rising sea levels, disturbances such as storms, drought, and climate change, which are combining to cause widespread impacts on ecosystems at the terrestrial-aquatic interface? One particular area of uncertainty is how these processes may mobilize soil organic carbon, resulting in changes in the dissolved or gaseous greenhouse gas (GHG) fluxes. We present results from the first year of a manipulative experiment looking at the effects of changes in salinity exposure and water availability on soil GHG fluxes. Large (40 cm diameter) soil cores were transplanted along natural salinity and elevation gradients in a Maryland, USA, coastal forest subject to rapid sea level rise. Comparative observations were also made in a western Washington, USA watershed with slow sea level rise but strong tidal fluctuations. Disturbed and undisturbed control cores allow us to distinguish transplant from salinity effects; soil respiration measurements were made every 7-10 days. Cores transplanted to lower-salinity sites, and to higher-elevation plots, exhibited elevated GHG fluxes relative to disturbance controls. These preliminary results suggest that changes in salinity exposure and water availability may exert significant effects on coastal forest GHG fluxes and the stability of soil carbon.
Forest soil is the largest carbon pool in terrestrial ecosystem, and the soil-to-atmosphere CO2 flux (soil respiration, Rs) is the main link between soil and atmosphere. However, due to the lack of integration of field observations, substantial uncertainties exist in quantifying large-scale soil carbon effluxes, which limit our understanding of the fate of forest soil in a warming world. Here, China’s forest ecosystems were divided into six forest types in six regions, and an integrated soil respiration database (N=634) was compiled to evaluate soil carbon effluxes by random sampling with replacement. Average annual Rs was 783 g C m-2 yr-1 across China, ranking from the highest to the lowest as follows: East, Southwest, South, Northwest, Northeast and North. Total soil carbon emissions were 1472.6 Tg C yr-1 in China’s forest ecosystems, and about 69% from three southern regions (i.e., Southwest, Southern China and Eastern China) and 31% from three northern regions (i.e., Northwest, Northern China and Northeast). Evergreen needleleaf forest (529.09 Tg C yr-1, 52%) and evergreen broadleaf forest (343.01 Tg C yr-1, 34%) were the main source of soil carbon emissions in three southern regions, while deciduous broadleaf forest (334.36 Tg C yr-1, 74%) was the main emissions in three northern regions. Our results provide a better understanding of the distribution and magnitude of soil carbon effluxes in China’s forest ecosystems.