黄河三角洲湿地柽柳周边土壤的水盐耦合关系

Tamarix chinensis on soil water and salt and its coupling relationship in the Yellow River Delta wetland

为揭示滨海湿地植物对土壤水盐的影响机制,以黄河三角洲湿地柽柳(Tamarix chinensis Lour.)周边土壤水、盐为研究对象,分析柽柳周边土壤水盐相互影响的耦合关系。结果表明:距柽柳远近不同,土壤含水率的差异明显不同,冠下表层土壤含水率明显大于冠缘和裸地,呈现由冠下至裸地逐渐减小的趋势,尤其是柽柳西、南两侧的变化趋势最为明显;20 cm土层以上水分聚集率为冠下大于冠缘,呈现明显的“水岛”效应,而20 cm以下水分聚集率的变化则相反;土壤盐分表聚性显著,远离柽柳的裸地表层土壤含盐量较高,西、南两侧最为明显;土壤总盐与Cl^(-)、Na^(+)、Mg^(2+)3种离子相关性极显著,这些离子在近柽柳周围土壤的变化幅度及含量均较小,盐分富集率明显为冠下小于冠缘,呈现“盐谷”效应;土壤水盐耦合度在柽柳周边表现为西侧>南侧>北侧>东侧,水、盐呈显著负相关;西、南两侧较高的土壤含盐量出现在低含水率的条件下,呈现高含盐量+低含水率为高耦合度的特征,这种高耦合度情况还出现在柽柳周边的表层土壤与远离柽柳的裸地。在柽柳的影响下,水盐耦合度呈现距柽柳由近及远逐步增大、随着土层深度的增加而逐渐减小的趋势。

The Yellow River Delta,the most comprehensive and youngest coastal wetland in China,exhibited the dual characteristics of abundant resources and fragile ecological environment.The severe soil salinization and halophytes play a critical role in salinization control.Tamarix chinensis was a typical halophyte adjusting water salt balance.So,the aim of this paper was revealing the mechanisms of plants impact on soil water and salt in coastal wetlands and providing scientific reference for the protection and restoration of coastal wetlands.The study focused on soil water and salt around Tamarix chinensis Lour in the Yellow River Delta wetland.The sample collection location was selected on the buffer zone on the south side of the Yellow River Delta Nature Reserve,which were the Tamarix communities with minimal human interference.A relatively independent tamarisk shrub with vigorous growth was selected in the community.Four sets of soil profiles were successively taken from north,south,east and west,each set consists of 4 soil profiles which were able to represent the status of the soil distancing 50 cm,100 cm,150 cm,and 200 cm from the root of the shrub.Each soil profile was layered in layers of 0-5 cm,5-10 cm,10-20 cm,20-40 cm and beneath 40 cm of the ground water level visible.the eight major ions(Cl^(−)、K^(+)、Na^(+)、Ca^(2+)、Mg^(2+))and moisture content in the soil were monitored.To reveal the influenced mechanism of coastal wetland plants on soil water and salt,the spatiotemporal characteristics and coupling relationship of soil water and salt around the habitat of Tamarix shrub in the Yellow River Delta were analyzed.The results showed that:The soil moisture content under the plant crown was significantly higher than that of the edge of plant crown and the bare ground and showed a trend of gradual decreasing from main stem of the Tamarix to far away.The water aggregating rate showed a clear“water island” pattern, in the soil layer above 20 cm, the accumulation rate under the plant crown was significantly higher than that of the crown edge, while the opposite was in the soil layer below 20 cm. Soil salt ions were well correlated with total salt, among which Cl^(−), Na^(+) and Mg^(2+) were significantly correlated, and the changes in the contents of three ions under the crown of tamarisk were relatively small in all directions of east, south, west and north. Due to the salt absorption by the root system of Chinese tamarisk, the enrichment rate of total salinity under the plant crown was less than that at the crown edge and showed a clear “salt valley” pattern. The high coupling degree of soil water-salinity appeared in the states of high salt content and low moisture content around the Tamarix shrub. The high coupling situation occurred in the surface soil around the tamarisk, on the south and west two sides, and in the bare land far from the tamarisk. At different directions around the shrub, the coupling degree of soil water-salinity was manifested as west > south > north > east. The soil water and salinity content showed the significant negative correlation. Under the influence of the Chinese Tamarisk, the coupling degree of water and salt appeared a gradually decreasing trend from far to near the Tamarisk. As the increase of the soil depth, the influence of external factors gradually weakens, and the coupling degree decreased with the increase of soil depth.