| Wetland plant is the product of wetland environment and it has a driving effect on the positive evolution of wetland ecosystem at the same time. In order to explore the relationship between wetland plants and soil nutrients and salinity cycling in wetland ecosystem, we select the Tamarix shrub of coastal native wetland in the Yellow River Delta. First hand information Based on the first hand information of vegetation survey and environmental monitoring, we have analyzed the distribution pattern of Tamarix population in Salsa- Tamarix community and Tamarix communities, have clarified the spatial distribution characteristics of nutrients and salinity about Tamarix shrub fertile island, reveal the mechanism of Tamarix island fertilizer and the relationship between fertilizer island effect and community succession in coastal native wetland. The results show that:(1)In terms of Tamarix population distribution pattern : Tamarix population shows the spatial pattern of random distribution in the Salsa- Tamarix community, with the increase of the sampling scale, there is a trend of the evolution of the random distribution to the cluster. Tamarix population shows the spatial distribution pattern of cluster in the Tamarix community, with the increase of the sampling scale, it trends in the evolution of random distribution.(2)In terms of soil nutrients characteristics of Tamarisk shrub fertile island under different distribution pattern: For the pattern of random distribution, in horizontal directions, the content of SOM, AN, AK of soil is significantly higher than shrub interspaces, but mostly it appears in the bottom of the soil(30-50 cm). In vertical direction, the soil nutrient index of Tamarisk shrub belongs to middle or bottom type. In directions, the SOM and AN are distributed uniformly in directions, AP gather in east and south, AK gather in west. In enrichment condition, Tamarisk shrub can gather SOM in the bottom and AN, AP and AK in all soil layers, enrichment rate is strong below the canopy than edge of canopy. Correlation analysis showed that there have positive correlations between nutrient indexes. For the pattern of cluster distribution, in horizontal directions, soil nutrient is significantly higher below the canopy surface layer than edge of canopy and shrub interspaces. In vertical direction, the soil nutrient index of Tamarisk shrub almost belongs to table type poly. In directions, all kinds of nutrients mostly gather west and south. In enrichment condition, tamarisk shrub can gather SOM, AN, AP and AK and enrichment capability is strong below the canopy than edge of canopy. On the correlation, there was a significantly positive correlation among various nutrient indexes. For the pattern of random distribution, the Tamarisk shrub soil formed a germ of fertile island and shrub gathered nutrient lowly. However, for the pattern of cluster distribution, the Tamarisk shrub soil has formed the characteristics of fertile island obviously, and it is remarkable that the shrub gathered nutrient.(3)In terms of soil salt characteristics of Tamarisk shrub fertile island under different distribution pattern: For the pattern of random distribution, in horizontal direction, soil pH value is less below the canopy than edge of canopy and shrub interspaces in all soil layers and soil pH value has no significant difference. The soil EC and SAL are significantly less below the canopy than edge of canopy and shrub interspaces in 30-50 cm depth. The salt ions have different change of gradient in horizontal direction: Na+ forms salt valley, K+?Ca2+?SO42- form salt island, CL- and HCO3- have no significant change. In vertical direction, the soil pH value of Tamarisk shrub belongs to neutral soil in 0-5cm, and the soil pH value belongs to sub alkaline soil in other layers. The salt gathers on the surface. In enrichment condition, Tamarisk shrub can reduce the EC?SAL?Na+ ?Mg2+ and CL-, and gather K+?Ca2+?SO42-?HCO3-. Correlation analysis showed that there has a significant negative correlation between the salt indexes. For the pattern of cluster distribution, in the horizontal direction, the soil pH value below the canopy is significantly lower than shrub interspaces in 5-10 cm, the soil EC and SAL are significantly less below the canopy and edge of canopy than shrub interspaces in 0-10 cm depth. For salt ions, Na+?Mg2+?CLforms salt valley and K+?Ca2+?SO42- forms salt island on the surface, HCO3- have no significant change. In vertical direction, the soil pH value belongs to neutral soil in 0-5cm, and the soil pH value belongs to sub alkaline soil in other layers. The salt gathers on the surface. In directions, the pH value value is evenly distributed and the salt gathers in west and south. In enrichment condition, Tamarisk shrub can reduce the Na+?Mg2+?CL-, and gather K+?Ca2+?SO42-?HCO3-. Correlation analysis showed that HCO3- had no significant correlation with the salt index and there have a significant negative correlation between the other salt indexes. For two kinds of spatial pattern, Tamarisk shrubs both can reduce the soil salt around the shrub. The surface soil forms salt valley for cluster distribution, while the deep soil forms salt valley for random distribution. This indicates that there have more significant salt valley effects under cluster distribution.(4)In terms of formation mechanism of fertile island and salt valley:The formation of Tamarisk fertile island is mainly determined by the small circulation of the material, which is caused by the litter, the residue of the animal and the root absorption effect. In addition, the runoff, animal disturbance, wind erosion and water erosion also played a certain effect. While the formation of salt Valley is the result of interaction effect of crop transpiration, root absorption, canopy leaching and shrub shelter. The fertile island and salt Valley of different salt ions is mainly determined by ionic selective absorption of root: When the absorption rate of ions is higher than that of the migration rate, the salt Valley is formed; on the contrary, the fertile island is formed.(5)The species diversity of Salsa-Tamarix community to Tamarix community and the change trend of Tamarix scrub soil salinity and nutrient of different community pattern have reflected the evolution process and direction of the Yellow River delta wetland ecosystem. In this process, the fertilizer island effect of Tamarix scrub has played an important role in the change of Tamarix population pattern and the increase of species diversity, which is one of the important factors to promote the evolution of wetland ecosystem. |
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