Different effects of NaCl and Na2SO4 on the carbon mineralization of an estuarine wetland soil

Abstract

NaCl and Na2SO4 salts often dominate in estuarine wetland soils. However, it is unclear how different salt types affect carbon mineralization as a response to salinity levels. In this study, soil samples (0–13 cm) collected in the Liaohe estuarine wetland were amended with NaCl and Na2SO4 salts at five salt levels: 1 mS·cm−1 (EC1), 3 mS·cm−1 (EC3), 5 mS·cm−1 (EC5), 10 mS·cm−1 (EC10) and 18 mS·cm−1 (EC18). The amended soils were incubated for 193 d, and the carbon mineralization rates were periodically measured. NaCl has decreased carbon mineralization at all salinity levels, but the effect of Na2SO4 was found only in the high salinity level (EC18). We found a significant ion-specific effect of salt types on carbon mineralization at the lower salinity levels (EC1, EC3 and EC5) but no significant ion-specific effect at the higher salinity levels (EC10 and EC18). The salt effects highly varied with incubation time and the time changes were depended on salt types. The results suggest that there may be a salinity threshold (5–10 mS·cm−1) that impacts the ion-specific effect (NaCl and Na2SO4) on carbon mineralization, depending on the salinity level and the ionic physiochemical behaviors.