Interacting Effects of Plant Invasion, Climate, and Soils on Soil Organic Carbon Storage in Coastal Wetlands

Coastal wetland soils store large amounts of organic carbon, which is becoming vulnerable to environmental changes such as exotic species invasion and climate change. Soil organic carbon (SOC) is also related to soil biogeochemical factors. To understand the mechanisms of these changes in regulating SOC, it is necessary to characterize the direct and indirect effects of exotic species invasion, climate, and soil variables on SOC. We used a structural equation model to identify the key driving mechanisms of SOC storage to a depth of 1 m at 15 sites on the East China coast, where Spartina alterniflora Loisel. (S. alterniflora) invasion has significantly influenced SOC storage. The model revealed several patterns that are expected to explain the enhanced SOC storage. Spartina alterniflora invasion had a direct effect on SOC storage mainly due to its impacts on biomass production. Temperature had an important influence on SOC storage and the subsurface SOC content. SOC storage was also related to the interacting effects of S. alterniflora invasion and soil biogeochemical properties such as soil salinity, fine soil fraction, and bulk density. The relative contribution of SOC in the topsoil to SOC storage at a depth of 1 m decreased over time, while the contribution increased for the SOC below the surface. These results highlight the interactions among S. alterniflora invasion, climate, and soil properties in regulating SOC dynamics. Our results imply that the relative importance of vertical patterns to SOC storage associated with S. alterniflora invasion and temperature fluctuations will change over time. Plain Language Summary The world's largest invasion of S. alterniflora is occurring in the coastal wetlands of China. Coastal wetland soils, which are vulnerable to exotic species invasions, contain large amounts of organic carbon. The controlling mechanisms of soil organic carbon (SOC) associated with S. alterniflora invasion and climate change may be complex due to the interrelationships that exist among ecological factors. In our study, we investigated the effects of plant invasion, climate, and soils on SOC storage and its vertical distribution. We found that SOC storage was enhanced over time. Spartina alterniflora invasion had a direct effect on SOC storage mainly due to its impacts on biomass production. Temperature had an important influence on SOC storage and the subsurface SOC content. The interacting effects of S. alterniflora invasion and soil biogeochemical properties such as soil salinity, fine soil fractions, pH, and bulk density were also identified as having crucial impacts on SOC storage. Our results suggest an interesting possibility that the relative contribution of vertical patterns to the SOC pool is likely to change over the invasion period.