Study on Investigation of Shrub Germplasm Resources and Community Succession in the Kongtong Mountain

In order to understand the structure of shrub communities and vegetation landscape in the Kongtong Mountain in different habitats,by using the line transect method,shrub communities and composition in the Kongtong Mountain were fully investigated,and the relationship between shrub communities and ecological environment,the community composition,structure,and vegetation landscape and succession of shrub communities in various habitats were systematically analyzed. The results showed that there were 142 species of shrubs,sub-shrubs and woody vines in the Kongtong Mountain,belonging to 75 genera,39 families. Except only two species of plants belonging to one genus,one family were gymnosperms,other species were angiosperms. Various shrub species had some spatial distribution characteristics,and their vertical distribution had certain hierarchy with the change of altitude. In the four conditions of slope direction,shrub community composition was different. There were 12 tree species in shrub communities on sunny slopes,and the constitutive species was S. davidii（ Franch.） Skeels. There were 14 tree species in shrub communities on semi-sunny slopes,and the constitutive species was H. rhamnoides Linn. There were 12 and 15 tree species in shrub communities on semi-shady and shady slopes,and the constitutive species was O. davidiana Decaisne. In the absence of external disturbances,the succession of shrub communities in the Kongtong Mountain began in bare wasteland and experienced natural grassland,mixed shrubs and grass,shrub community and sub-shrub community（ single dominant communities） during the period. Finally,shrub communities evolved into arbor communities.

The driving force of water resource stress change based on the STIRPAT model:take Zhangye City as a case study

A prominent contradiction between supply and demand of water resources has restricted local development in social and economic aspects of Zhangye City,located in a typical arid region of China.Our study quantified the Water Resource Stress Index(WRSI)from 2003 to 2017 and examined the factors of population,urbanization level,GDP per capita,Engel coefficient,and water consumption per unit of GDP by using the extended stochastic impact by regression on population,affluence and technology(STIRPAT)model to find the key factors that impact WRSI of Zhangye City to relieve the pressure on water resources.The ridge regression method is applied to improve this model to eliminate multicollinearity problems.The WRSI system was developed from the following three aspects:water resources utilization(WR),regional economic development water use(WU),and water environment stress(WE).Results show that the WRSI index has fallen from 0.81(2003)to 0.17(2017),with an average annual decreased rate of 9.8%.Moreover,the absolute values of normalized coefficients demonstrate that the Engel coefficient has the largest positive contribution to increase WRSI with an elastic coefficient of 0.2709,followed by water consumption per unit of GDP and population with elastic coefficients of 0.0971 and 0.0387,respectively.In contrast,the urbanization level and GDP per capita can decrease WRSI by−0.2449 and−0.089,respectively.The decline of WRSI was attributed to water-saving society construction which included the improvement of water saving technology and the adjustment of agricultural planting structures.Furthermore,this study demonstrated the feasibility of evaluating the driving forces affecting WRSI by using the STIRPAT model and ridge regression analysis.

Litter decomposition in fragile ecosystems:A review

As a linkage between plants and soil,litter decomposition and its effect on nutrient recirculation have an important ecolog‐ical significance as they contribute to soil structure improvement and the restoration of degraded ecosystems.Fragile eco‐systems in arid regions(both hot and cold)are depleted in soil organic matter,and as a result of various factors their circu‐lation of material and energy is slower.Here we discuss how litter decomposition is necessary to maintain the stability of fragile ecosystems.We reviewed research on litter decomposition carried out in arid regions.Our objective in this review is to outline how litter decomposition,and the subsequent buildup of organic matter in soil,is a key process determining the stability of fragile ecosystems.Our review shows that existing studies have focused on the influence of single ecologi‐cal factors on litter decomposition and nutrient cycling,and highlights how the exploration of interactions among factors determining litter decomposition is still lacking.This interaction is a key aspect,since in the real world,decomposition and nutrient return to soil of litter products is affected by multiple factors.We propose a network setup on a cross-regional scale using standardized methods(e.g.,the tea bag method)to understand litter decomposition and nutrient return in frag‐ile ecosystems.Such a unique network could contribute to establish predictive models suitable for litter decomposition and nutrient return in these areas,and thus could provide theoretical and practical support for regional ecological protec‐tion and high-quality development.