杭州湾滩涂Na元素含量对植物多样性和优势度的影响

Effects of soil Na content on plant diversity and dominance in the wetland of the Hangzhou Bay

钠元素是滩涂湿地土壤盐分的最主要成分。利用样方法调查了杭州湾滩涂湿地的植物多样性及其分布,以及土壤钠含量对植物多样性和优势度的影响,用相关回归方法对数据进行分析处理。结果表明:(1)海塘内的物种多样性要高于海塘外,有11种植物,优势植物是芦苇(Phragmites australis)和互花米草(Spartina alterniflora),且互花米草的优势度要高于芦苇;但是在海塘外的自然滩涂,则只出现3种植物,主要优势植物是互花米草和海三棱藨草(Scirpus xmariqueter),芦苇则较为少见。在海塘外的海三棱藨草-互花米草混合群落中,海三棱藨草的优势度要高于互花米草。(2)物种丰富度指数(Margalef指数)和物种多样性(Simpson指数)指数均与土壤钠含量呈极显著负相关关系,通过回归分析得回归方程分别为y(Margalef指数)=-0.05x+1.608(R2=0.732,P<0.01,n=10),y(Simpson指数)=-0.038x+1.214(R2=0.926,P<0.01,n=10)。(3)海塘内互花米草的重要值与土壤钠含量呈极显著正相关,y=0.033x-0.007(R2=0.802,P<0.01,n=10);而芦苇重要值则与其呈极显著负相关,y=-0.013x+0.419(R2=0.607,P<0.01,n=10)。在海塘外的混合群落中,互花米草和海三棱藨草的重要值与土壤钠含量之间没有明显的相关关系。(4)随着(海塘)围垦时间的延长,其物种多样性呈现增大的趋势,中生植物更为丰富,而盐生植物逐渐萎缩。

Soil salinity which is closely related to sodium （Na） content greatly affects vegetation pattern in beach wetlands. Tidal flat reclamation is a popular way to increase land area in coastal regions of East China, leading to landscape change and successional development towards mesophytic communities in beach wetlands. The Hangzhou Bay is a world-famous estuary gulf with extremely strong tide, i.e. the Qianjiang Tide, and located in the vicinity of northeastern Zhejiang Province in East China. The Andong Wetland located in Cixi City of Zhejiang Province along the Hangzhou Bay is a key spots for northeast Asian birds migration in China. However, it has been strongly affected by human activities, especially reclamation; effects of human activities on vegetation and soil traits have not been studied yet. To investigate the effect of reclamation on soil Na content and on the relationship between Na content and vegetation pattern, we surveyed plant communities inside and outside the seawall （affected and not affected by reclamation） by transect sampling method in the Andong Wetland from 2003 to 2005. We also collected soil samples and determined soil Na content by X-ray fluorescence analysis. We calculated Margalef index and Simpson index as measures of species diversity and importance value as a measure of plant dominance. Species diversity was higher inside than outside the seawall. Vegetation inside the seawall consisted of 11 plant species, which was relatively more dominated by mesophytes than that outside. Inside the seawall the most dominant species was Spartina alterniflora and the second most dominant was Phragmites australis. However, only three species （Sp. alterniflora, Scirpus xmariqueter and P. australis） occurred in the natural wetland outside the seawall, and Sp. and Sc. xmariqueter were the two dominants. Both the Margalef index （ R^2 = 0. 732, P 〈 0.01 ） and the Simpson alterniflora index （ R^2= 0.924, P 〈 0.01 ） were negatively correlated with soil Na content. Inside the seawall, soil Na content was positively correlated with the important value of Sp. alterniflora （ R^2 = 0.802, P 〈 0.01 ）, but negatively correlated with that of P. australis （R^2 =0.607, P 〈 0.01 ）. However, outside the seawall, soil Na content was significantly correlated with the importance value of neither Sp. alterniflora nor Sc. xmariqueter. With increasing duration since reclamation, number of mesophytes increased, whereas that of halophytes decreased. We conclude that long-term land reclamation significantlydecreases soil salinity which greatly influences plant species diversity and dominance in wetlands.