FLUXES OF CO2 AND CH4 UNDER DIFFERENT TYPES OF COASTAL SALT MARSHES OF THE YELLOW RIVER DELTA: DYNAMIC CHANGES AND DRIVING FACTORS ACROSS DIFFERENT SEASONS - Salt Marshes - page 46

2007), due to C/N regulations and interactions of other abiotic variables at spatial scale
(Huang et al., 2002). Generally, the variation of TN, NO 3 — N and NH 4 + -N in this study were
in contrast to the CO 2 and CH 4 fluxes, suggesting that nitrogen had inhibitory effect on CO 2
and CH 4 emissions. The results were similar with that of Jang et al. (Jang, 2012) and Zhang et
al. (Zhang et al., 2007). High nitrogen content can not only weaken enzymatic activity, but
also combine with lignin, thereby reducing the decomposition of organic matter
(Krasakopoulou, 2009).
The measurement of CO 2 and CH 4 emissions with static-chamber and GC methods
include the respiration and breakdown products of the vegetation and the underground part
(root, microorganisms, etc.). The CO 2 fluxes of vegetation followed the order: T. chinensis >
P. australis > S. salsa > bare land, which the same order as the alignment of plant biomass of
these sample sites. In addition, CO 2 flux peak period occurred at the vegetation growing
season, suggesting that vegetation respiration made a great contribution to CO 2 emissions.
Jiang (2012) found that CO 2 fluxes of the undamaged vegetation sampling site were higher
than that of the damaged site, illustrated that the vegetation was a key influence factor of CO 2
fluxes. The impact can be carried out through the followed ways: 1) photosynthesis and
respiration of vegetation; 2) Plant roots secretion can provide the substrate for soil
microorganisms, to promote the activity and respiration of microorganism; 3) Plants can
transport oxygen to the root, provide aerobic environment, and accelerate the mineralization
of organic matter(Duan et al., 2005); Laanbroek (2010) found that Methane emissions from
vegetated sediment usually exceed those from unvegetated sediments. But in our study, with
the exception of bare land, the vegetation communities were all act as CH 4 sink. The reason
may be as followed: 1) CH 4 from bare land can be send to atmosphere through the water and
soil; 2) The oxidation of vegetation rhizosphere is the main way of CH 4 oxidation (Duan et
al., 2005).
C ONCLUSION
We aimed to figure out the variations of CO 2 and CH4 fluxes and their associated
environmental factors in the coastal salt marshes ( T. chinensis , S. salsa , P. australis and bare
land) of the Yellow River estuary. Results have demonstrated that:
1) Coastal marshes in the Yellow River Delta acted as a CO 2 source. CO 2 fluxes ranged
from 2.287 to 331.371 mg/(m 2 ·h) and emission peak appeared in summer. The
annual average flux was 77.101 mg/(m 2 ·h); CH 4 fluxes ranged from -0.075 to 0.185
mg/(m 2 ·h) and average flux was 0.0026 mg/(m 2 ·h). The sample sites acted as a week
CH 4 sink in spring and summer, while CH 4 source in autumn and winter. The
maximum CH 4 flux occurred in summer and autumn respectively.
2) The CO 2 fluxes of different ecosystems followed the order: bare land (16.264
mg/(m 2 ·h)) < S. glauca (64.784 mg/(m 2 ·h)) < P. australis (119.430 mg/(m 2 ·h)) < T.
chinensis (167.138 mg/(m 2 ·h)). All the sample site acted as CO 2 sources; CH 4 fluxes
of different ecosystems followed the order: T. chinensis (-0.012 mg/(m 2 ·h)) <
S.glauca (-0.006 mg/(m 2 ·h)) < P. australis (-0.006 mg/(m 2 ·h)) < bare land (0.037