Effect of Water Supply on Seed Germination of Soil Seed-bank in Desert Vegetation

在温室条件下 ,进行了水涝和保湿 2种水分供应试验。结果表明 ,在土壤种子库中 ,有 3种植物的种子在水涝条件下的萌发数量明显较大 ;9种植物在保湿条件下的萌发数量明显较大 ;18种植物在 2种水分供应条件下的萌发数量没有明显差异。当植物的土壤种子密度较低时在不太合适的萌发条件下表现为不存在。研究结果强调在进行土壤种子库分析之前预备萌发试验的必要性。同时也揭示出利用一种标准的水分供应处理方法去分析来自不同生境土样里种子库的危险性。

Spatial-temporal dynamics of desert vegetation and its responses to climatic variations over the last three decades:a case study of Hexi region in Northwest China

Analysis of spatial-temporal variations of desert vegetation under the background of climate changes can provide references for ecological restoration in arid and semi-arid areas. In this study, we used the Global Inventory Modeling and Mapping Studies （GIMMS） NDVI data from 1982 to 2006 and Moderate Resolution Imaging Spectroradiometer （MODIS） NDVI data from 2000 to 2013 to reveal the dynamics of desert vegetation in Hexi region of Northwest China over the past three decades. We also used the annual temperature and precipitation data acquired from the Chinese meteorological stations to analyze the response of desert vegetation to climatic variations. The average value of NDVImax （the maximum NDVI during the growing season） for desert vegetation in Hexi region increased at the rate of 0.65x10-3/a （P〈0.05） from 1982 to 2013, and the significant increases of NDVImax mainly appeared in the typical desert vegetation areas. Vegetation was significantly improved in the lower reaches of Shule and Shiyang river basins, and the weighted mean center of desert vegetation mainly shifted toward the lower reaches of the two basins. Almost 95.32% of the total desert vegetation area showed positive correlation between NDVImax and annual precipitation, indicating that precipitation is the key factor for desert vegetation growth in the entire study area. Moreover, the areas with non-significant positive correlation between NDVImax and annual precipitation mainly located in the lower reaches of Shiyang and Shule river basins, this may be due to human activities. Only 7.64% of the desert vegetation showed significant positive correlation between NDVImax and annual precipitation in the Shule River Basin （an extremely arid area）, indicating that precipitation is not the most important factor for vegetation growth in this basin, and further studies are needed to investigate the mechanism for this phenomenon.

Water sources for typical desert vegetation in the Ebinur Lake basin

In arid and semi-arid environments,desert vegetation plays an important role in preventing soil erosion by wind and helps maintain the stability of desert and oasis ecosystems.Four types of typical desert vegetation,namely Populus euphratica,Haloxylon ammodendron,Nitraria sibirica,and Halostachs caspica,corresponding to different habitats(i.e.,river bank,sand dune,desert,and salt marsh)were chosen as the model vegetation in this research.Theδ^(2)H andδ^(18)O for rainwater,soil water,and plant water were applied to identify the water sources and quantify the proportions of different water sources used over the entire plant growth period(from March to October).The results showed that the precipitationδ^(2)H andδ^(18)O in the Ebinur Lake basin varied from-142.5‰to-0.6‰and from-20.16‰to 1.20‰,respectively.The largestδ^(2)H andδ^(18)O values occurred in summer and the smallest in winter.The soil waterδ^(2)H andδ^(18)O of the four habitats decreased gradually with increasing depth.Theδ^(2)H andδ^(18)O values of water extracted from the stems of the four plants had similar variation trends,that is,the maximum was observed in spring and the minimum in summer.Among the four plants,H.caspica had the highest stable isotopic values in the stem water,followed by N.sibirica,H.ammodendron,and P.euphratica.The water sources and utilization ratios of desert vegetation varied across different growth stages.Throughout the growing period,H.ammodendron mainly used groundwater,whereas the water source proportions used by N.sibirica varied greatly throughout the growing season.In spring,plants mainly relied on surface soil water,with a contribution rate of 80%-94%.However,in summer,the proportion of deep soil water used was 31%-36%;and in autumn,the proportion of middle soil water used was 33%-36%.H.caspica mainly relied on topsoil water in spring and autumn,and the proportion of soil water in the middle layer slightly increased to 20%-36%in summer.P.euphratica mainly used intermediate soil water in spring with a utilization rate of 53%-54%.In summer,groundwater was the main source,with a utilization rate of 72%-88%,and only 2%-5%came from river water,whereas in autumn,the river water utilization rate rose to 11%-21%.The results indicated that there were significant differences in water use sources during the growing period for desert vegetation in arid areas.This research provides a theoretical basis for understanding water use mechanisms,water adaptation strategies,and vegetation restoration and management in arid areas.

Parallel Study on Potential and Existing Geographical Distribution of Haloxylon Dominated Desert Vegetation in China

By applying ARC/INFO (NT version) of the GIS software package , we extracted the existing geographicaldistribution ofHaloxylon dominated desertvegetationandproduced athematicmap ofgeographical distribution of theexisting Haloxylon dominated desert vegetation based on the newly published Vegetation Atlas of China;we defined the adaptiveparameter range ofgeographical and climate ofHaloxylon dominated desert vegetation to generate the potential geographical distribution map of Haloxylon dominated desert vegetation with thesupport of GREEN software. We then sliced and compared the existing and thepotential distribution maps. The results show that the potential geographical distribution areas of Haloxylon ammodendron and Haloxylon persicum dominated desert vegetation accord with the existing distribution areas in the administration division, and the topographic types in both the distribution areas are similar. However, the borders of different directions ofthe potential H. ammodendron dominated desert vegetation distribution has surpassed 0.4° to 5.9° of the existing borders. The borders of different directions of the potential H. persicum dominated desert vegetation has surpassed 0.9° to 3.3° of the existing borders. In China, the existing geographical distributionalarea ofH. ammodendron dominated desertvegetation accounts for 9.1% of the potential one in China and the proportion of the existing H. persicum dominated desert vegetation distribution area to the potential areais 34.1%. The result of comparison of the potential and the existing distribution areaof Haloxylon dominated desert vegetation can provide important scientific basisfor the recovery, reconstruction and introduction of Haloxylon dominated desertvegetation.

Comprehensive evaluation on the ecological function of groundwater in the Shiyang River watershed

With an arid climate and shortage of water resources,the groundwater dependent ecosystems in the oasis-desert ecotone of the Shiyang River Watershed has been extremely damaged,and the water crisis in the oasis has become a major concern in the social and the scientific community.In this study,the degene-ration characteristics of the groundwater ecological function was identified and comprehensive evaluated,based on groundwater depth data,vegetation quadrat and normalized difference vegetation index(NDVI)from Landsat program.The results showed that(1)the suitable groundwater depth for sustainable ecology in the Shiyang River Watershed is about 2-4 m;(2)the terms of degenerative,qualitative and disastrous stages of the groundwater ecological function are defined with the groundwater depths of about 5 m,7 m and 10 m;(3)generally,the groundwater ecological function in the oasis-desert ecotone of the lower reaches of Shiyang River Watershed is weak with an area of 1397.9 km2 identified as the severe deterioration region,which accounted 74.7%of the total area.In the meantime,the percentages of the good,mild and moderate deterioration areas of groundwater ecological function are 3.5%,5.5%and 16.3%,respectively,which were mainly distributed in the Qingtu lake area and the southeastern area of the Shoucheng town;(4)the degradation and shrinkage of natural oasis could be attributed to the dramatic groundwater decline,which is generally caused by irrational use of water and soil resources.This study could provide theoretical basis and scientific support for the decision-making in environmental management and ecological restoration of the Shiyang River Watershed.

Application of Holdridge life-zone model based on the terrain factor in Xinjiang Automous Region

This study improved the application of the Holdridge life-zone model to simulate the distribution of desert vegetation in China which gives statistics to support eco-recovery and ecosystem reconstruction in desert area. This study classified the desert vegetation into four types： （1） LAD： little arbor desert; （2） SD： shrub desert： （3） HLHSD： half-shrub, little half-shrub desert; （4） LHSCD： little halfshrub cushion desert. Based on the classification of Xinjiang desert vegetation, the classical Holdridge life-zone model was used to simulate Xinjiang desert vegetation＇s distribution and compare the Kappa coefficient result of the model with table of accuracy represented by Kappa values. The Kappa value of the model was only 0.19, it means the simulation result was poor. To improve the life-zone model application to Xinjiang desert vegetation type, a set of plot standards for terrain factors was developed by using the plot standard as the reclassification criterion to climate sub-regime. Then the desert vegetation in Xinjiang was simulated. The average Kappa value of the second simulation to the respective climate regime was 0.45. The Kappa value of final modeling result was 0.64, which is the better value. The modification of the model made it in more application region. In the end, the model＇ s ecological relevance to the Xinjiang desert vegetation types was studied.

Vegetation biomass dynamics in a desert ecosystem in NW China

Subject Code:D01With the support by the National Natural Science Foundation of China,a collaborative study by Prof.Wang Xinping(王新平)from the Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences and the research group led by Prof.Ignacio Rodriguez-Iturbe from