Effects of Spartina invasions on blue carbon sequestration in China

1. Coastal wetlands are large reservoirs of soil carbon (C) and have been invaded globally by the exotic species <i>Spartina alterniflora</i>. However, the effects of these invasions on blue C sequestration remain unclear. 2. Here, we conducted a meta-analysis of 2479 soil organic C (SOC) observations collected from 91 field studies in coastal China, the world’s largest introduced range for <i>S. alterniflora</i>. 3. Our results show that <i>S. alterniflora</i> invasions had no significant effect on SOC in vegetated native coastal wetlands in China. <i>S. alterniflora</i> increased the SOC in the top 30 cm of salt marshes after invading only one of the nine types of native marshes, the native marsh was dominated by a dwarf succulent species, <i>Suaeda salsa</i>, in the northern subtropics, and decreased the SOC in the top 60 cm of mangrove habitats after invasion in the southern subtropics. <i>S. alterniflora</i> invasions did not significantly affect the SOC in salt marshes or mangroves dominated by other native species. Therefore, the C sequestration capacity of <i>S. alterniflora</i> does not differ from those of most native dominant species. Moreover, the SOC in <i>S. alterniflora</i>-invaded ecosystems increased on only a decadal-scale and then decreased, rather than increasing monotonically as was previously thought. 4. 1. <i>Synthesis and applications</i>. Our findings reveal that<i> S. alterniflora</i> invasions apparently increase the blue C sink in China only in native ecosystems dominated by specific species in specific regions and only over short time periods. Therefore, the expansion of <i>S. alterniflora</i> should not be considered as a natural climate solution to increase C sink in coastal China. Instead, future efforts are required to eradicate <i>S. alterniflora</i> preferentially in the coastal wetlands where<i> S. alterniflora</i> invasions do not increase C sinks, and to conserve and restore native coastal wetlands nationwide for increasing both ecological integrity and C sinks and mitigate climate change.