Characteristics Of Soil And Herb Communities In Dongtan Reclamation Area Of Chongming Island, Shanghai

As the main pattern to expand land resources of littoral, reclamation becomes the only way to supplement land resources of Shanghai. Dongtan of Chongming Island had been reclaimed many times, the proportion of reclamation area had risen to176km2in2002. Researches were mostly concentrated on ecological system in the tidal bank of Dongtan, but less in the reclamation area. Based on the characteristics of soil and herb communities in different reclamation areas, this dissertation studied the process of soil development and vegetation succession in Dongtan. This research chose6vestigation sites which had obvious boundaries of reclamation years, and the sample collection was done in the summer of2012. Soil samples of cultivated land, woodland and unused land were divided into seven depths, including0～5cm,5～10cm,10～20cm,20～40cm,40～60cm,60～80cm and80～100cm. At the same time, the quadrat investigation was done in6random herb communities of different reclamation years. Through the preliminary studies on the vertical variation of soil physicochemical factors, including pH value, moisture, electrical conductivity, and the content of organic matter, total nitrogen, total phosphorus, research on the relationship between soil factors and land-use types, reclamation time was done. Through the quadrat investigation on herb communities, this dissertation studied the species composition and diversity of herb communities and explored the vegetation succession process in Dongtan reclamation area. Following are the main results:1The correlation between reclamation years and soil factors, including pH value, moisture, and the content of organic matter, total nitrogen, total phosphorus, was significant. The content of organic matter was the main indicator of soil development in Dongtan reclamation area. With the increasing duration of reclamation, soil pH value decreased, and reaching neutral. The content of soil organic matter increased with the increasing duration of reclamation in50a, and the positive correlation between content of soil organic matter and total nitrogen was significant.2The correlation between land-use types and soil factors, including moisture content, electrical conductivity and the content of total nitrogen, total phosphorus, was significant. Due to irrigation and fertilization, soil moisture and the content of total nitrogen, total phosphorus were high in cultivated land. The man-made woodland of Dongtan led deficiencies in shrub and herb layer. It affected the soil water storage, so the soil moisture was the lowest. Because of corruption of litter grottoes, the content of soil organic matter, total nitrogen and total phosphorus increased. Due to the herb communities on the unused land, the soil water storage was better than woodland, so soil moisture was higher. The herb communities were in the growth stage, and the demand of organic matter, total nitrogen and total phosphorus was high, so it resulted in low values of these three kinds of soil nutrient content, especially in the0-20cm surface soil.3The correlation between soil depth and soil moisture, electrical conductivity and the content of organic matter, total nitrogen, total phosphorus was significant. Human activity played a important role in the soil depth of0-60cm soil, so the soil factors had large fluctuations and the content nutrient was high. However, human activity affected weakly on the soil depth of60～100cm, so its soil factors were relatively stable.4In the investigation area, a total of49herb species were recorded, belonging to20families and45genera, among which, Compositae had12genera and13species, Gramineae had7genera and9species, these two families had a total of19genera and22species, occupied about45%of the total. Annual herbs dominated in the herb communities, and the important value of perennial herbs was growing slowly with the increasing duration of reclamation.5With the increasing duration of reclamation, the diversity of herb communities decreased after an initial increased. Within20years, the species richness and diversity increased slowly, while evenness and dominance showed an opposite trend. The Jaccard index and Cody index both increased, which proved that the competition among each species was fierce and community structure was astable. From20to40a, the Jaccard index and Cody index reached the peak value, and species richness and diversity increased significantly, which showed that the community structure became more complex. From40to50a, the diversity increased slowly, with the peak value in the50years of reclamation. The Jaccard index and Cody index kept decreasing, that showed the herb community structure didn’t reach stable. After50years of reclamation, the diversity showed a slight downward with the increasing duration of reclamation.6Soil pH value, moisture and electrical conductivity were at the moderate level from30to50years of reclamation. Meanwhile the species richness and diversity both reached their peak values. Dongtan reclamation area was by the sea, soil salinity(electrical conductivity) was the main soil factor affecting diversity. Soil moisture had a correlation with diversity, and the diversity was risen with the increasing of the content of soil nutrients. Vegetation and soil were interrelated and interacted on each other, that was suitable soil environment had a positive effect on vegetation succession, and natural vegetation succession was an effective way to improve soil quality.