Study On Soil Carbon And Nitrogen Storage After Restoration Of Native Vegetation In The Chongming Dongtan Wetland

The coastal wetlands are identified as one of the most productive ecosystems on earth,also as the huge carbon sinks and nitrogen pools due to a positive function of carbon and nitrogen accumulation by vegetation.Therefore,the coastal wetlands play an important role in alleviating the regional increase in atmpospheric CO₂concentration and global warming.The Chongming Dongtan wetland in the Yangtze Estuary,which is an important part of coastal wetlands in China,is a typical estuarine wetland with high sedimentation.Scirpus mariqueter is an endemic marsh vegetation species at China's coastal zone,and is also an important constructive species of coastal wetlands in the Yangtze Estuary.The S.mariqueter marshes provide many important ecological services,including carbon consequeation,promoting deposition,wave attenuation and embankment protection.However,reclamation and invasion of Spartina alterniflora have seriously threatened the habitat of S.mariqueter during the past three decades.Since 2010,a large ecological engineering aiming to control S.alterniflora and to improve bird habitat was carried out in the Chongming Dongtan wetland.Although the exotic S.alterniflora had been effectively eliminated,the restoration of native S.mariqueter and the consequent evaluation of ecological profit were ergently needed.The carbon and nitrogen accumulation after S.mariqueter restoration was identified as one of important reference index.This study compared the effects of revegetation mode?planting density?,community age?newly restoration and mature marsh?and site properties?sediment texture and sedimentary dynamics?on the plant gowth,soil nutrient concentration,soil organic carbon?SOC?and total nitrogen?SN?accumulation.The main results and conclusions of this study are shown as below:?1?The sediment texture of the eastern and southern parts of Chongming Dongtan wetland was different.The sediment in the eastern tidal flat was mainly composed of fine mud with small grain size?named as M-site?,and the soil bulk density was relatively low.In the southern tidal flat,the sediment was mainly composed of coarse silt with large grain size?named as S-site?,and the soil bulk density was relatively high,probably due to effect of strong hydrological disturbance.The content of available nitrogen,available phosphorus and available potassium in the eastern tidal flat was higher than that in the southern tidal flat.Moreover,the previous monitoring on sedimentary dynamics showed that the eastern tidal flat was characterized by moderate sediment accretion,while a weak erosion trend was observed in the southern tidal flat.?2?After a two-year revegetation period,the shoot density and total biomass of S.mariqueter with high?M-Y_H?and medium planting density?M-Y_M?were significantly higher than that in the revegetation area with low planting density?M-Y_L?.The shoot density and total plant biomass of new formed S.mariqueter marsh in S-site?S-Y_H?were significantly lower than that in the M-site with different planting densities.In the M-site,shoot density and aboveground biomass with M-Y_H approximated to 80%of mature S.mariqueter marsh?M-O?.However,in the S-site,shoot density and aboveground biomass with S-Y_H only approximated to only 28%and 14%of mature S.mariqueter marsh?S-O?,respectively.Small soil grain size?with low bulk density?and smooth sediment deposition in the M-site might benefit vegetation growth and population recovery,compared to the S site.This study also found that there was a positive correlation between the vegetation biomass and the content of soil available nitrogen,yet a weak negative correlation between the vegetation biomass and the content of soil available phosphorus and available potassium was detected.?3?The SOC stock increased with the restoration of S.mariqueter marsh and increase in plant biomass growth,which higher than SN.Both the SOC and SN storage and belowground biomass were mainly distributed in the depth of 0-20 cm,and the correlation between them indicated that the distribution of vegetation roots in soil may affect the vertical distribution of carbon and nitrogen.The SOC storage in the M-Y_H area was significantly higher than that in the M-Y_M and M-Y_L area,but there was no significant difference of SOC storage between M-Y_M and M-Y_L.The SN stock increased with the increase in plant biomass growth,but the difference among the three planting densities was not significant.The SOC and SN stocks in the newly restored marsh of M-Site?regardless of planting densities?were significantly higher than that in the S-Y_H area.The SOC and SN storage increased with the increase in community age,and the trend was pronounced in the M-site.In the M-site,the SOC and SN stocks in the newly restored marsh were 1.14-1.52 and 1.17-1.22 times over that in the unvegetative zone?bare flat?,respectively.The SOC stock in the M-Y_H area was equivalent to 75%in the M-O area.However,the SOC and SN stocks in S-Y_H were only 1.05 times over that of bare flat.Although high planting density was applied,the SOC stock in the S-Y_H area was only 59%in the S-O area,significantly lower than that in M-Site.In conclusion,the SOC and SN stocks and the content of soil available nitrogen,available phosphorus and available potassium were modified by S.mariqueter restoration and the degree depended on the revegetation intensity,community age and site properties.Earlier success of vegetation restoration played a key role in determining the SOC and SN accumulation in the marshes.The tidal flat with muddy sediments and moderate deposition rate was favorable for the settlement and growth of S.mariqueter,and the SOC and SN accumulation rate was also rapid.On contrary,the tidal flat with silty sediments and poor sedimentary conditions?even erosion?was unfavorable for the S.mariqueter revegetation and carbon and nitrogen accumulation.