孔雀河下游断流河道的环境特征及物种间关系

基于孔雀河下游断流河道的环境因子和植被样地数据,采用聚类与CCA排序法,分析了生境的退化特征以及物种间的相互关系,结果表明:1)断流河道退化生境分为绿洲-荒漠过渡类型、轻度荒漠化类型和盐土荒漠化类型。绿洲-荒漠过渡类型地下水位低、盐分含量相对较低,植被盖度相对较高,土壤维持着原砂质壤土,为潜在退化型;轻度荒漠化类型地下水位、土壤质地与含盐量与前者基本相同,土壤未明显退化,但植被盖度低于10%,植物种类与个体数目都较低,属于轻度退化型;盐土荒漠化类型地下水位高、盐分含量高,土壤机械组成中砂粒比重较大、无建群种幸存,属于重度退化型。2)绿洲-荒漠过渡类型总体联结性为显著正联结,正负联结比小于1,生态系统表现为建群种维系物种关系的不稳定状态;轻度荒漠化类型总体联结性为不显著负联结,正负联结比小于1,表现出生态系统进入退化演替的阶段;盐土荒漠化类型总体联结性为显著正联结,正负联结比大于1,表现出重度退化群落的种间平衡状态,物种间以达到稳定共存,其中,真盐生植物对这种平衡的维持起着重要的作用。3)CCA排序表明,绿洲-荒漠过渡类型形成以胡杨为中心的种间正联结,幸存于盐分适中、水分养分相对较高的生境;轻度荒漠化类型,形成以多枝柽柳与刚毛柽柳相互依存的不显著负联结,幸存于土壤养分、水分相对较低的生境;盐土荒漠化类型形成以盐爪爪、盐节木、盐穗木等真盐生植物维系的显著正联结,幸存于土壤贫瘠、地下水位浅、盐分含量高、沙化严重的生境。

Environmental characteristics and interspecific associations in the lower reaches of the Kongque River

The interaction between plants and the environment, especially the interspecific associations in certain ecosystems, is an important ecological topic. The Kongque River originates from Boston Lake and flows through the east of the Taklamakan Desert; it plays a critical role in supplying water and ecological stability to the South Korla and Lop Nur regions. Owing to climate change, and excessive human exploitation, water availability has become increasingly limited, resulting in severe ecological degradation in the lower reaches of the Kongque River. Therefore, to evaluate the degree of ecological degradation and potential restoration probability in the lower reaches of the Kongque River, this study focused on the interspecific associations of the degraded desert riparian ecosystem by analyzing the groundwater, soil salinity, soil nutrients, and vegetation in 2013. The results showed that: 1) Based on the variation in groundwater depth, soil salinity, soil type, vegetation coverage, species richness, and species diversity, the longitudinal habitats in the lower reaches of the Kongque River could be divided into three types: oasis-desert ecotone, intermediate desertification zone, and saliniferous desertification zone. In the oasis-desert ecotone, the groundwater depth was soil salinity was low, Populus euphratica was the constructive species in plant community, vegetation coverage varied from 9.04% to 21.10%, and the soil was mainly formed by sandy loam. The groundwater depth, soil salinity, and soil texture in the intermediate desertification zone were similar to those in the oasis-desert ecotone. However, the vegetation coverage, species diversity, and species biomass were lower than those in the oasis-desert ecotone. Tamarix ramosissima Ledeb. and T. hispida Willd. were the constructive species of the plant community. The groundwater depth and soil salinity in the saliniferous desertification zone were the highest among the three zones, and sand grain factor affecting the soil. Owing to the severe environmental factors, P. euphratica and Tamarix spp. could not survive; therefore, the desert halophytes, such as Halostachys caspica C. A. Mey, and Kalidium foliatum Moq. were the constructive species in the plant community. 2) Overall, inter-specific associations between different species in the lower Kongque River were not significant. Most of the pairwise associations in the oasis-desert ecotone were positive. Nevertheless, associated coefficients were <1, which indicated that the ecological stability of the ecotone was vulnerable. The pairwise association in the intermediate desertification zone was not significantly negative, and the association coefficients were also <1. This finding implied that the environmental factors were highly heterogeneous, and the ecosystem was deteriorating. The pairwise association in the saliniferous desertification zone was significantly positive, and most of associated coefficients were >1, for all the survival species in this zone were euhalophytes. Consequently, the ecological degradation in this zone was the most serious. 3) A canonical correspondence analysis showed that in the oasis-desert ecotone, the key species, P. euphratica showed a positive association with other species, the habitat expressed characteristics of moderate soil salinity, high nutrients, and suitable soil moisture. Unlike the oasis-desert ecotone, associations among species in the intermediate desertification zone were not significant, the two key species, T. hispida and T. ramosissima, were interdependent, and the habitat was characterized as having lower soil nutrient and water contents. In the saliniferous desertification zone, associations among euhalophytes such as Kalidium foliatum, Halocnemum strobilaceum, and Karelina caspica were significantly positive, and the characteristics of the habitat were barren soil, a shallow groundwater level, and high salt salinity.