This paper expounds on the meaning of migration and the status quo of studies at home and abroad on migration and ecological migration. It focuses on the discussion of the necessity of ecological migration in Xinjiang...This paper expounds on the meaning of migration and the status quo of studies at home and abroad on migration and ecological migration. It focuses on the discussion of the necessity of ecological migration in Xinjiang, and the problems faced by the ecological emigrants, such as the lack of water, the serious land salination and basification, sand storms, and the adaptation to the environment. Besides, it probes into the problems existing in the ecological migration, including the unscientific design of the moving project, the defects of the reclamation work, and the irrational treatment of the relation between ecological migration and regional development. Based on this, we put forward some suggestions about and countermeasures against those problems.展开更多
Soil food web structure is fundamental to ecosystem process and function; most studies on soil food web structure have focused on agro-ecosystems under different management practices and natural terrestrial ecosystems...Soil food web structure is fundamental to ecosystem process and function; most studies on soil food web structure have focused on agro-ecosystems under different management practices and natural terrestrial ecosystems,but seldom on greenhouses. This study explored the static and temporal variability of soil food structure in two greenhouses of Shandong Province,North China over a two-year period. The static properties were measured directly by surveying functional group composition and a series of parameters portraying the species properties,link properties,chain properties and omnivory properties of the web,as well as indirectly through calculation of nematode indices,enrichment index(EI),structure index(SI),and channel index(CI). The dynamic variability of greenhouse soil food structure was described by the dynamics of functional groups,Bray-Curtis(BC) similarity and cluster analysis. The results showed that the greenhouse soil food web contained 14 functional groups,with microbes having the highest mean biomass,followed by protozoa. Of the three functional groups of protozoa,flagellates were the dominant group on most sampling dates,amoebae only became the dominant group during the summer,while ciliates were the least prevalent group. All nematodes were assigned into one of the four functional groups,bacterivorous,fungivorous,herbivorous and omnivorous,and the fungivorous nematodes had the lowest mean biomass. Mites were assigned into three functional groups and the omnivorous noncryptostigmatic mites were the dominant group. All the functional groups showed significant seasonal changes. The soil food web connectance was 0.15,the maximum food chain length was 5,and the average food chain length was 3.6. The profiles of the EI and SI showed that the food web was resourcedepleted with minimal structure. The results of CI indicated that the bacterial decomposition pathway was the dominant pathway in the food web of the greenhouse soils studied and the results of BC similarity showed that the soil food web had higher variability and instability over time. The cluster analysis showed that the functional groups located at high trophic levels with low biomass were in a cluster,whereas those at low trophic levels with high biomass were closer. Compared with the food web structure of agroecosystem and natural terrestrial ecosystem soils,the structure of greenhouse soil food web was simple and unstable,which was likely driven by high agricultural intensification,particularly over application of fertilizers.展开更多
文摘This paper expounds on the meaning of migration and the status quo of studies at home and abroad on migration and ecological migration. It focuses on the discussion of the necessity of ecological migration in Xinjiang, and the problems faced by the ecological emigrants, such as the lack of water, the serious land salination and basification, sand storms, and the adaptation to the environment. Besides, it probes into the problems existing in the ecological migration, including the unscientific design of the moving project, the defects of the reclamation work, and the irrational treatment of the relation between ecological migration and regional development. Based on this, we put forward some suggestions about and countermeasures against those problems.
基金Supported by the National Natural Science Foundation of China(No.40901116)
文摘Soil food web structure is fundamental to ecosystem process and function; most studies on soil food web structure have focused on agro-ecosystems under different management practices and natural terrestrial ecosystems,but seldom on greenhouses. This study explored the static and temporal variability of soil food structure in two greenhouses of Shandong Province,North China over a two-year period. The static properties were measured directly by surveying functional group composition and a series of parameters portraying the species properties,link properties,chain properties and omnivory properties of the web,as well as indirectly through calculation of nematode indices,enrichment index(EI),structure index(SI),and channel index(CI). The dynamic variability of greenhouse soil food structure was described by the dynamics of functional groups,Bray-Curtis(BC) similarity and cluster analysis. The results showed that the greenhouse soil food web contained 14 functional groups,with microbes having the highest mean biomass,followed by protozoa. Of the three functional groups of protozoa,flagellates were the dominant group on most sampling dates,amoebae only became the dominant group during the summer,while ciliates were the least prevalent group. All nematodes were assigned into one of the four functional groups,bacterivorous,fungivorous,herbivorous and omnivorous,and the fungivorous nematodes had the lowest mean biomass. Mites were assigned into three functional groups and the omnivorous noncryptostigmatic mites were the dominant group. All the functional groups showed significant seasonal changes. The soil food web connectance was 0.15,the maximum food chain length was 5,and the average food chain length was 3.6. The profiles of the EI and SI showed that the food web was resourcedepleted with minimal structure. The results of CI indicated that the bacterial decomposition pathway was the dominant pathway in the food web of the greenhouse soils studied and the results of BC similarity showed that the soil food web had higher variability and instability over time. The cluster analysis showed that the functional groups located at high trophic levels with low biomass were in a cluster,whereas those at low trophic levels with high biomass were closer. Compared with the food web structure of agroecosystem and natural terrestrial ecosystem soils,the structure of greenhouse soil food web was simple and unstable,which was likely driven by high agricultural intensification,particularly over application of fertilizers.
