Zhao RuiFeng

Spatial patterns of ephemeral plants in Gurbantünggüt Desert

In the present research, the authors measured parameters of richness, cover and importance value of ephemeral and ephemeroid plants on south-north and east-west transects in the Gurbantünggüt Desert in early spring, and investigated and analyzed the microhabitats, such as terrain, geomorphology, soil physical-chemical properties and crusts. By comparison, the regional differences in the ephemeral distribution in the desert were revealed. The species of ephemeral plants in the south and center are the richest and those in the west are the poorest in the desert. The cover of ephemeral plants in the mid-south is higher than that in the north, and that in the mid-east is higher than that in the west. The response of ephemeral plants to the spatial variation of the desert habitat forms the population-habitat gradient of ephemeral plants. The characteristics are: (1) In the habitat with higher terrain, coarser textured soil with poorer sorting and correspondingly higher organic matter and lower alkali-saline contents, Carex physoides and Eremopyrum orientale are the dominant ephemeral plants; (2) In the dry habitat with lower terrain, looser textured soil, some organic matter, alkali-saline soil, and developed crust, the ephemeral plants Alyssum linifolium and Erodium oxyrrhynchum are of characteristic of drought and alkali-saline tolerance; (3) In the habitat with lower terrain, some water and more alkalisaline soil, the ephemeral plants Neotorularia torulosa and Hypecoum parviflorum being of alkali-saline tolerance are mainly developed. However, most ephemerals are distributed in a habitat order of higher terrain, some organic, and less alkali-saline soil on the above-mentioned ephemeral population-habitat gradient. The spatial gradient of variation in desert microhabitats is small, and as a whole, the physiological character of mesophytism is represented by the desert ephemerals.

Seasonal variation of soil respiration under different land use/land cover in arid region

Through combining the soil respiration with the main environmental factors under the planting shelterbelt (Populus woodland) and the natural desert vegetation (Tamarix ramosissima+Phragmites communis community and Haloxylon ammodendron community) in the western Junngar Basin, the difference in soil respiration under different land use/land cover types and the responses of soil respiration to temperature and soil moisture were analyzed. Results showed that the rate of soil respiration increased with temperature. During the daytime, the maximum soil respiration rate occurred at 18:00 for the Populus woodland, 12:00 for T. ramosissima+Ph. communis community, and 14:00 for H. ammodendron community, while the minimum rate all occurred at 8:00. The soil respiration, with the maximum rate in June and July and then declining from August, exhibited a similar trend to the near-surface temperature from May to October. During the growing season, the mean soil respiration rates and seasonal variation differed among the land use/land cover types, and followed the order of Populus woodland > T. ramosissima+Ph. communis community > H. ammodendron community. The difference in the soil respiration rate among different land use/land cover types was significant. The soil respiration of Pouplus woodland was significantly correlated with the near-surface temperature and soil temperature at 10 cm depth (P<0.01) in an exponential manner. The soil respiration of T. ramosissima+Ph. communis and H. ammodendron communities were all linearly correlated with the near-surface temperature and soil surface temperature (P<0.01). Based on the near-surface temperature, the calculated Q10 of Populus woodland, T. ramosissima+Ph. communis community and H. ammodendron community were 1.48, 1.59 and 1.63, respectively. The integrated soil respiration of the three land use/land cover types showed a significant correlation with the soil moisture at 0–5 cm, 5–15 cm and 0–15 cm depths (P<0.01). The quadratic model could best describe the relationship between soil respiration and soil moisture at 0–5 cm depth (P<0.01).

Fragmentation process of wetlands landscape in the middle reaches of the Heihe River and its driving forces analysis

Heihe River is one of the most important inland rivers in the northwest arid district of our country.Wetlands that distributed along the middle Heihe River Basin has a great significance to the eco-environment safety of northwestern regions in our country.It plays a key role in preventing the Tengger Desert and Badain Jaran Desert to be a whole.However,it had been destructed by human activities and climate change deeply in recent years.So the research of the wetlands in Heihe River is urgently needed.Based on satellite images of 1975,1987,1992,2001 and 2010,the paper chose some typical landscape index models,such as patch density,landscape internal habitat area index,mean patch size,FS and so on,to analyze the wetland landscape fragmentation process and its drivers of the middle Heihe River Basin between 1975 and 2010,combining with grey relational analysis,principal component analysis and other analytical methods.The results indicated that fragmentation process of wetland landscape in the middle reaches of the Heihe River mainly expressed as the shrinkage of internal habitat area and mean patch size,the increase of fragmentation index and the enlargement of FS in the past 35 years.In the entire period of study,the mean patch size of the wetlands in middle Heihe River Basin decreased 48.95 hm2 corresponding to the patch density raised 0.006 Ind/hm2.In terms of patch shape fragmentation index,it mainly expressed as the increasing of mean patch shape fragmentation index and area-weighted mean shape fragmentation index.Especially the values of the mean patch shape fragmentation index and area-weighted mean shape fragmentation index increased from 0.524,0.269 to 0.556 and 0.276 between 1992 and 2010.So it can draw a conclusion that wetland landscape fragmentation has been the main manifestations of wetland degradation in the study area throughout the study period.The dominant driving force which led to the middle reach of the Heihe River wetland landscape fragmentation and development is human factors.Natural factors on the process of wetland landscape fragmentation have a certain influence.Yet the contribution of human activities on the wetland landscape fragmentation was significantly higher than the natural factors in a smaller time scale.The increased capacities as well as the expanding influence sphere of human activities act as the main cause of the middle reach of the Heihe River wetland landscape fragmentation.In addition,natural factors also have some influence on the process of wetland landscape fragmentation.Furthermore,the impact of natural factors on the process of wetland landscape fragmentation is mainly reflected in the temperature and precipitation.Comparing with precipitation,in the natural context of arid environments just like the study area,the temperature plays a significantly greater actor in the process of wetland landscape fragmentation.