| Coastal wetland is an important carbon sink of the earth's ecosystem.Salt marsh vegetation,as an important source of soil organic carbon,has a significant impact on the content and composition of soil organic carbon.Invasion of alien vegetation,Spartina alterniflora,will increase or decrease the soil carbon pool.At present,the explanation of the stability of soil organic carbon for Spartina alterniflora invasion on soil carbon pools is increasingly drawing attention from scholars at home and abroad.Therefore,in order to reveal the effect of Spartina alterniflora invasion on soil carbon pool composition and stability in the subtropical coastal wetland ecosystem in China.In this paper,we focus on a case study of Beihai,Zhanjiang,Zhangjiangkou,Yunxiao,Jiulongjiang estuary,Culudao,Shanyutan,Yueqing bay,Hengsha island and Chongming island,which are located in China's five provinces and cities such as Guangxi,Guangdong,Fujian,Zhejiang and Shanghai as the study areas.Compared the invasive species(Spartina alterniflora)and native plants(Avicennia marina,Kandelia candel and Phragmites australis)soil organic carbon content(SOC)and soil organic carbon storage(SOCS),the ease of oxidation of carbon(EOC),microbial biomass carbon(MBC),dissolved organic carbon(DOC)and soil carbon release(CO2 and CH4)from the soil,and analyzed the physical,chemical and microbiological mechanisms of soil organic carbon after the invasion of Spartina alterniflora.The results indicated:(1)The soil organic carbon(SOC)content of Avicennia marina,Kandelia candel,Phragmites australis and Spartina alterniflora were ranged from 5.72?21.05 g/kg,12.57?28.06 g/kg,15.34?30.89 g/kg and 4.50?31.80 g/kg,respectively.In general,SOC content was decreased after Spartina alterniflora invasion mangrove(Avicennia marina and Kandelia candel),and SOC content was increased after invasion of Phragmites australis.The change of SOC storages were consistent with SOC after Spartina alterniflora invasion.(2)The content of soil active organic carbon(EOC,MBC,DOC)in Avicennia marina and Spartina alterniflora were changed from 2.67?7.93 g/kg,69.90?746.05 mg/kg,33.99?205.36 mg/kg and 1.31?7.58 g/kg,54.60?620.72 mg/kg,38.72?106.65 mg/kg,respectively.The contents of EOC,MBC and DOC in the soil of Kandelia candel and Spartina alterniflora were between 2.33?6.30 g/kg,96.14?525.93 mg/kg,42.13?102.39 mg/kg and 2.42?6.90 g/kg,30.69?714.92 mg/kg,32.87?125.38 mg/kg respectively.The content of active organic carbon(EOC,MBC,DOC)in the Phragmites australis and Spartina alterniflora were ranged from 0.95?7.64 g/kg,109.81?453.81 mg/kg,38.04?183.05 mg/kg and from 1.68?5.33 g/kg,188.95?524.68 mg/kg,52.74?246.78 mg/kg,respectively.In general,the soil EOC and DOC did not change significantly(p>0.05)after Spartina alterniflora invaded different indigenous plants,while MBC content of Spartina alterniflora was decreased after invaded mangrove forest,and MBC was increased after invasion of Phragmites australis.(3)The cumulative CO2 emission in 0-10 cm,10-20 cm,20-30 cm and 30-40 cm of Avicennia marina and Spartina alterniflora were 407.77,349.12,307.78,311.24 ?g/g and 327.48,373.24,358.29,325.68?g/g in Zhanjiang,respectively.The Kandelia candel and Spartina alterniflora in the Culudao were 296.83.180.96,281.67,251.28?g/g and 281.68,229.71,319.86,247.51?g/g,respectively.Phragmites australis and Spartina alterniflora in the Shanyutan were 271.43,205.83,198.94,252.08 ?g/g and 251.63,234.38,255.35,278.46?g/g,respectively.In general,Spartina alterniflora increased soil cumulative CO2 release.(4)The cumulative CH4 release from soils in different soil layers of Zhanjiang,Culudao and Shanyutan showed that:the release of CH4 cumulative showed that 20-30 cm>30-40 cm>0-10 cm>10-20 cm in the Culudao and Shanyutan,Zhanjiang Avicennia marina was 10-20 cm(48.09 ng/g)>0-10 cm(35.92 ng/g)>20-30 cm(28.70 ng/g)>30-40 cm(26.16 ng/g),while the accumulative release of CH4 from Spartina alterniflora was 20-30 cm(59.39 ng/g)>10-20 cm(45.52 ng/g)>0-10 cm(38.54 ng/g)>30-40 cm(27.47 ng/g).As a whole,Spartina alterniflora increased the cumulative release of soil CH4.(5)Spartina alterniflora invasion did not significantly change the grain-size distribution characteristics of the aggregates in the surface layer(0-10 cm)and the distribution of organic carbon in each grain size in the Zhanjiang,Culudao and Shanyutan(p>0.05).The results showed that the aggregates MWD,GMD and DR0.25 were increased by 48.40%,34.21%and 33.38%respectively,and the D was decreased by 6.72%after invasion of Avicennia marina.The aggregates MWD,GMD and DR0.25 increased by 16.86%,10.84%and 16.94%,and the D decreased by 10.07%respectively after invasion of Kandelia candel.However,the soil aggregates MWD,GMD and DR0.25 were decreased by 23.18%,23.16%and 21.53%,and D was increased by 34.07%.(6)The content of Ca-SOC in surface soils in Zhanjiang,Culudao and Shanyutan was ranged from 0.52 to 0.74 g/kg,Fe(Al)-SOC content was from 2.58 to 7.01 g/kg,The SOC content was ranged from 10.14 to 24.65 g/kg.Further calculation showed that the Ca-SOC/SOC ratio of Spartina alterniflora was higher than that of native plants,and the ratio of[Fe(Al)-SOC+residual state SOC]/SOC was lower than that of native plants(p>0.05).(7)The ratio of fungi/bacteria in surface soil increased,after Spartina alterniflora invaded Avicennia marina of Zhanjiang and Kandelia candel of Culudao.While that of fungi/bacteria decreased after invasion of Phragmites australis in Shanyutan.(8)EOC/SOC of soil under Avicennia marina and Spartina alterniflora in the surface layer were(19.12± 2.14)%and(23.19 ± 1.81)%,respectively in Zhanjiang,under Kandelia caandel and Spartina alterniflora were(16.87 ± 0.92)%and(23.34 ±1.33)%,respectively in Culudao.In the surface soil of under Phragmites australis and Spartina alterniflora in Shanyutan were(15,09 ± 1.82)%and(17.09 ± 1.15)%,respectively.On the whole,the EOC/SOC of ratio in the surface was increased after Spartina alterniflora invaded different native plants.The content of soil non-active organic carbon in soil was also calculated.The content of soil non-active organic carbon in the surface layer of Spartina alterniflora in Zhanjiang,Culudao and Shanyutan were betweemn 13.08 g/kg,15.47 g/kg and 20.26 g/kg,which were significantly lower than native plants(14.45 g/kg,22.47 g/kg,24.51 g/kg).The content of non-active organic carbon in surface soil after Spartina alterniflora invasion was significantly decreased(p<0.05).(9)Comparing the soil aggregates physical,chemical bonding and microbial stability indicators with the soil organic carbon stability represented by EOC/SOC and inactive organic carbon content,the mechanism of soil chemical bonding stability may be the dominant mechanism that influences the change of soil organic carbon stability after Spartina alterniflora invasion. |
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