Effects Of Spartina Alterniflora Invasion On Soil Physicochemical Properties In Coastal Wetlands Of Huangjiatang Bay

Spartina alterniflora is one of the most important invasive species in coastal wetland in China,which seriously threatens the safety and sustainable development of coastal wetland ecosystem.Taking huangjiatang Bay Wetland as the research object,based on remote sensing image interpretation,the distribution and diffusion speed of Invasive Species Spartina alterniflora in huangjiatang Bay Wetland were studied.Combined with field survey sampling and indoor experimental analysis,the changes of soil carbon(C),nitrogen(N),phosphorus(P)content and and further explored the effects of soil physical and chemical properties(particle size,magnetic susceptibility,p H)on soil C,N,P The results are as follows:(1)Since 2007,Spartina alterniflora has appeared in huangjiatang Bay Wetland and distributed sporadically.The growth rate of Spartina alterniflora distribution area in the early stage was slow.In 2008 and 2014,Spartina alterniflora distribution area was 1.25 hm²and 2.90 hm²,respectively.The average annual expansion multiple from 2008 to 2014 was 0.15.Since 2014,the propagation and diffusion of Spartina alterniflora has increased rapidly.By 2019,its distribution area has reached 21.3 hm²,and the annual expansion multiple from 2014 to 2019 is 0.49.The aboveground biomass and total biomass of Spartina alterniflora increased year by year with the invasion years.(2)The grain size composition of the Guangtan wetland and Spartina alterniflora invasion wetland was mainly composed of sand and silt.However,the silt and clay contents increased with the increase of invasion years of Spartina alterniflora,especially the grain refinement was obvious after 8 and 12 years of invasion.The mass magnetic susceptibility of the Guangtan wetland was higher than that of the Spartina alterniflora wetland,and was positively correlated with sand content,negatively correlated with clay and silt content,while the frequency magnetic susceptibility was opposite,indicating that the developed root system of Spartina alterniflora had a certain weakening effect on the hydrodynamics of the coastal wetland.(3)Soil organic carbon(TOC)content in the Guangtan wetland and Spartina alterniflora invasion wetlands ranged from 0.79 to 2.27g/kg and 1.80 to 10.52g/kg,respectively,indicating that the TOC of Spartina alterniflora invasion also showed an overall trend of increase,and increased with the invasion years.In the vertical direction,the TOC content in the profile of Guangtan wetland is basically the same.The distribution of TOC content in the profile at the early stage of Spartina alterniflora invasion(Y-2 and Y-5)is similar to that of Guangtan wetland.The TOC content in the middle and upper layer(0?40cm)of the profile increases significantly in 8 and 12 years of invasion.(4)The contents of total nitrogen(TN)in the Guangtan wetland and Spartina alterniflora wetland ranged from 0.60 to 0.70g/kg and 0.47 to 1.10g/kg,respectively,indicating that Spartina alterniflora invasion had no significant effect on TN.In the vertical direction,the TN of Y-12 patches in the upper and middle layer was significantly higher than that in the bottom layer,and the other patches had no obvious differentiation in profile.Guang Tan wetland soil ammonium nitrogen(NH₄⁺-N)and nitrate nitrogen(NO₃^--N)content in the range of 7.67?12.67mg/kg,respectively 0.77?1.15mg/kg,each flower rice grass wetland soil NH₄⁺-N and NO₃^--N content in the range of 5.67?14.67mg/kg,0.26?3.29mg/kg,show that each flower rice grass invasion influence on wetland soil NH₄⁺-N was not significant,but to some extent increase NO₃^--N content,and is especially significant in the invasion of 12performance.In the vertical direction,NH₄⁺-N reached the maximum value at0?20cm,and the fluctuation decreased with the increase of profile depth,while NO₃^--N content peaked at different depths in different patches.(5)The contents of total phosphorus(TP)in the wetlands were 252.65?331.66mg/kg and 268.44?414.51mg/kg,respectively,indicating that the TP content was increased by Spartina alterniflora invasion.In the vertical direction,TP increased with the increase of Spartina alterniflora invasion years in the upper and middle sections.Inorganic phosphorus(IP)was the main component of wetland TP,and calcium and phosphorus(Ca-P)were the main components of IP.With the increase of invasive years of Spartina alterniflora,the contents of organic phosphorus(Org-P)and iron,aluminum and phosphorus(Fe/Al-P)in the soil increased,while the contents of Ca-P decreased.(6)There was a significant positive correlation between TOC,TN and TP,which indicated that they had mutual feedback coupling relationship.The contents of TOC,TN,TP,Org-P and Fe/Al-P were positively correlated with the percentage of silt and clay,but negatively correlated with the percentage of sand.With the extension of invasion years,the contents of the above indexes increased in varying degrees,indicating that the invasion of Spartina alterniflora reduced the hydrodynamic force,increased the percentage of clay and silt,refined the soil texture,increased the specific surface area,and had a negative impact on nutrients Adsorption and fixation were enhanced.In addition,with the extension of invasion years,the biomass of Spartina alterniflora increased,which was also conducive to the accumulation of nutrients.There was a significant negative correlation between soil NO₃^--N and p H,which was mainly due to the decrease of p H caused by the invasion of Spartina alterniflora,which promoted nitrification and then affected NO₃^--N content.There was a significant negative correlation between soil Fe/Al-P and p H,which may be due to the transformation of some insoluble P forms under the action of organic acids,resulting in the increase of Fe/Al-P content.