Responses of Plant Community Change on Wetland Degradation in Yellow River Delta Region

Abstract

As a result of climate change, oil field development, and increased human activity, the wetlands of the Yellow River Delta region of China exhibit regional degradation. To investigate the mechanism of wetland degradation and biodiversity changes, we performed a vegetation survey and a soil property analysis, including soil enzyme activity, in the Yellow River Delta region. The results reveal that at the Imperata (Imperata cylindrical) community stage, the soil is slightly alkalized, and the soil surface salinity is generally less than 0.3 %. Under such conditions, Imperata can grow and develop well, with good soil structure, low soil bulk density, high porosity, high fertility, and high soil organic matter content, which are conducive to plant growth. If the vegetation is not destroyed, the soil remains at this stage or further improves. When the salinity increases, the soil gradually becomes unsuitable for Imperata growth, and halophytes begin to appear, forming a halophyte community stage. At this stage, soil salinity increases, surface salinity increases to 0.8 % or higher, and the soil has a more compact structure, higher soil bulk density, and lower porosity. When vegetation degrades to a Suaeda glauca community stage, soil salinity further increases and evolves into a severe saline-alkali soil, with significantly augmented soil salinity, enhanced salinization, compact soil texture, poor permeability, and lower soil fertility. Further degradation of wetlands leads to vegetation disappearance, leaving bare land with only sporadic S. glauca. The soil environment is extremely harsh, with a high salt content, the soil is compact and sterile, and the organic matter content is merely 2.4 g/kg. In such an environment, plants have difficulty growing. Thus, vegetation evolution and degradation of wetlands occur almost simultaneously. Soil salinity accelerates the reverse succession of phytocoenosium, which in turn shifts the physical and chemical properties of soil toward a bad direction for plant growth. The two factors complement each other and are closely related. Analysis of different stages of community succession showed that, along with the degradation succession of vegetation, the physical and chemical properties of soil cause the corresponding changes, with a gradually increased degree of soil salinity.