| Biological invasion is one of the most core issues of global change since it significantly affects the biodiversity and the key biogeochemical processes of ecosystem.Spartina alterniflora,native to the Atlantic coast of North American,was introduced in 1979 to protect coastal dikes and to reduce coastal erosions from tides.It is currently distributed in 10 provinces of China,in which the area of Jangsu,Shanghai,Zhejiang and Fujian provinces accounts for 94.13%of the total distribution area.In recent years,the consequences of S.alterniflora invasion on the cycle of the native elements of wetland in coastal zone have attracted more and more attention from scholars.Although a great deal of researches has been carried out on it,most of the existing researches have focused on the carbon cycling and nitrogen cycling,There is still lack of comprehensive and profound understanding of the nutrient cycling mechanism of the primary wetland under the influence of its invasion.especially for the key mechanism of sulfur and other microelements biological cycling.In this paper,the invasive species of S.alterniflora and the native species of Cyperus malaccensis in the marsh of the Min River estuary were selected as study objects.The temporal and spatial distribution characteristics of total sulfur(TS)and inorganic sulfur(H2O-Sulfur,Adsorbed-Sulfur,HCl-Soluble-Sulfur,HCl-Volatile-Sulfur)in native marsh soil under the influence of S.alterniflora invasion were studied.The characteristics of sulfur accumulation,the decomposition of sulfur nutrient and the ecological of marsh plants were discussed,during the invasion of S.alterniflora.The sulfur cycling compartment model of marsh plant-soil(water)system under the influence of sd.alterniflora invasion was established.On the basis of the evaluating its sulfur cycle,the mechanism of sulfur competition of S.alterniflora invading the native marsh was illuminated.The main results were drawn as follows:(i)TS contents and S reserves of soils increased significantly after S.alterniflora nvasion.The TS contents of soils(0-60cm)in invaded and invading were respectively 1.21 and 1.20 times.TS contents in different types of soils was the lowest and fluctuated little in surface soils.With the increase of depth,TS contents increased and fluctuated greatly.High sulfur nutrient accumulation ability and nutrient return capability of S.alterniflora and the change of soil particle grades,pH,organic matter,soluble salt and soil moisture of soils under the influence of invasion are the main reasons leading to the increase of soil sulfur stocks.(ii)The Total Inorganic Sulfur(TIS)contents of different types of marsh soils were as follows:spring>winter>autumn>summer.TIS contents of soil(0-60 cm)in S.alterniflora marsh(after invasion)and ecotone marsh(during invasion)were 1.25 times and 1.21 times as much as those in C malaccensis marsh(before invasion),respectively,and which indicated that the available sulfur contents in marsh soils was increased by S.alterniflora invasion.The contents of HCl-Soluble-S and HCl-Volatile-S in soils of S.alterniflora marsh and ecotone mash were higher than those of C.malaccensis in different seasons,while the contents of H2O-S and Adsorbed-S were only higher in winter and spring than in the C.malaccensis marsh before invaded.and the soil soluble salt,pH,organic matter and the absorption ability of plants to available sulfur nutrients were the key factors affecting the occurrence and distribution of inorganic sulfur in different forms.(iii)The SO42-concentration in pore water of S.alterniflora marsh and ecotone marsh soils increased significantly in winter,spring and autumn,but the concentration of SO42-in pore water with both soils was significantly lower than the C.malaccensis mash before invaded by S.alterniflora In summer(especially in July),in which influenced by the absorption and utilization of plants.The effect of plant absorption and utilization is that the concentration of SO42-in pore water of different types of marshes is highest in winter,followed by autumn,and lower in summer and spring.While the SO42-concentration in the interstitial water of different types of marshes varies slightly in the vertical direction,and the overall performance increases with the depth.(iv)The ecological characteristics of S.alterniflora and C.malaccensis were obviously changed due to the competition of the two plants,and S.alterniflora had stronger underground reproduction ability and competitive advantage.Although the sulfur accumulation coefficient of all organs of S.alterniflora after invasion was lower than that of C.malaccensis except leaves,the TS contents and sulfur accumulation of different organs of S.alterniflora were significantly higher than those of the latter.The TS content and sulfur accumulation coefficient of S.alterniflora roots in the econote marsh were lower than that of C.malaccensis,but the sulfur accumulation coefficient of aboveground organs was higher than C.malaccensis.While TS content and accumulation coefficient in roots of S.alterniflora in econote marsh showed an increasing trend in general,but the C.malaccensis was opposite.The main factors affecting TS content in marsh plants were soil sulfur storage and the capacity of sulfur accumulation in plants.(v)The litters decomposition rate of S.alterniflora in after invasion and during invasion were 0.0056 d-1,0.0058 d-1,respectively,and which was significantly lower than the C.malaccensis that the litters decomposition rate in during invasion and before invasion were 0.0081 d-1 and 0.0074 d-1.but relative to the two pure communities,the decomposition rate of S.alterniflora and C.malaccensis in etonoce increased by 3.57%and 9.46%,respectively.Salt and substrate mass are the key factors to cause the difference of decomposition rate between S.alterniflora and C.malaccensis,while pH and nutrient conditions of marsh lead to the difference of decomposition rate of the same plant which in different marshes.Although the contents of TS in different types of plants residues fluctuated and increased during decomposition,they all showed different levels of sulfur release.The decomposition rate of sulfur in S.alterniflora decreased significantly after invasion and during invasion,and the lower C/S was the decisive factor for the rapid release of sulfur from native plant residues.Study on the assessment of sulfur biological cycling in marsh plant-soil(water)system under the influence of S.alterniflora invasion found that the marsh sulfur storage of soil(water),plant and litter have significantly increased by invasion of S.alterniflora,and the S.alterniflora could maintain its competitive advantage by improving its capacity of absorption and utilization of sulfur nutrients in the process of competition with native species of C.malaccensis.In addition,S.alterniflora can also maintain its sulfur nutrient supply capacity in its roots by reducing its sulfur cycling coefficient during invasion,and may accelerate tillering by increasing the supply capacity of underground sulfur nutrients,in order to further maintain its competitive advantage in the invasion process.Although the sulfur supply capacity of S.alterniflora increased obviously after invasion,but because of the instability of soil sulfur pool,the plant subsystem of the newly invaded S.alterniflora marsh is relatively unstable.Therefore,the unstable subsystem of S.alterniflora after its recent invasion can be fully utilized,and the sulfur nutrient supply level in marsh by human intervention to reduce the competitive advantage of S.alterniflora,which is favorable for maintaining the stabilization of the native species(C.malaccensis)... |
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