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 Spartina
alterniflora. 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 S. alterniflora.

3. Our
results show that S. alterniflora invasions had
no significant effect on SOC in vegetated native coastal wetlands in China. S. alterniflora 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, Suaeda salsa, in the northern subtropics, and decreased the
SOC in the top 60 cm of mangrove habitats after invasion in the southern subtropics.
S. alterniflora invasions did
not significantly affect the SOC in salt marshes or mangroves dominated by
other native species. Therefore, the C sequestration capacity of S. alterniflora does not differ from
those of most native dominant species. Moreover, the SOC in S. alterniflora-invaded ecosystems increased on
only a decadal-scale and then decreased, rather than increasing monotonically
as was previously thought.

4. 1. Synthesis and applications. Our findings
reveal that
S. alterniflora 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 S. alterniflora should not be considered as a natural climate
solution to increase C sink in coastal China. Instead, future efforts are
required to eradicate S. alterniflora
preferentially in the coastal wetlands where
S. alterniflora 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.