Short-term C4 plant Spartina alterniflora invasions change the soil carbon in C3 plant-dominated tidal wetlands on a growing estuarine Island

Spartina alterniflora is an invasive C-4 perennial grass, native to North America, and has spread rapidly along the east coast of China since its introduction in 1979. Since its intentional introduction to the Jiuduansha island in the Yangtze River estuary, Spartina alterniflora community has become one of the dominant vegetation types. We investigated the soil carbon in the Spartina alterniflora community and compared it with that of the native C-3 Scirpus mariqueter community by measuring total soil carbon (TC), soil organic carbon (SOC), total soil nitrogen (TN), and the stable carbon isotope composition (delta C-13) of various fractions. TC and SOC were significantly higher in Spartina alterniflora in the top 60 cm of soil. However, there was no significant difference in soil inorganic carbon (IC) between the two communities. Stable carbon isotopic analysis suggests that the fraction of SOC pool contributed by Spartina alterniflora varied from 0.90% to 10.64% at a soil depth of 0-100cm with a greater percentage between 20 and 40cm deep soils. The delta C-13 decreased with increasing soil depth in both communities, but the difference in delta C-13 among layers of the top 60cm soil was significant (p < 0.05), while that for the deeper soil layers (> 60 cm) was not detected statistically. The changes in delta C-13 with depth appeared to be associated with the small contribution of residues from Spartina alterniflora at greater soil depth that was directly related to the vertical root distribution of the species. (c) 2006 Elsevier Ltd. All rights reserved.