Oasis-desert Transitional Zone Research Articles

Characteristics of quartz grains in the middle and lower reaches of the Hutubi River, NW China, and its paleo-environmental significance

Quartz sand characteristics in the downstream floodplain of the Hutubi River, located near the oasis–desert transition zone at the southern edge of the Gurbantunggut Desert, were examined to understand the sedimentary dynamics and processes. By analyzing three fluvial–lacustrine–eolian profiles and collecting surface sediment samples from different reaches of the Hutubi River, the characteristics of quartz sand were examined using optically stimulated luminescence (OSL) dating and scanning electron microscopy (SEM). The qualitative and quantitative results reveal spatial variations in surface sedimentary quartz sand, reflecting a transition from glacial–hydraulic interaction to alluvial dominance, followed by a balance between eolian and alluvial processes, and ultimately eolian dominance. The quartz sand within the profiles exhibits sub-rounded and rounded shapes, with significant alluvial-pluvial characteristics, indicating a predominance of fluvial processes within the lower sections of the profiles, while the upper sections exhibit a higher occurrence of eolian microstructures. Overall, the study area experienced a shift from a relatively high-energy and stable depositional environment during the mid-Holocene to a relatively low-energy and unstable condition in the Late Holocene. This was evidenced by stable fluvial–lacustrine deposition between 8 and 6ka and subsequent transitions between high and low-energy hydraulic processes, accompanied by wind erosion and frequent changes in sedimentary environments since 4.2ka.

Patterns of salt transport and factors affecting typical shrub in desert-oases transition areas

Soil salinization and water deficits are considered the primary factors limiting economic development and environmental improvement in arid areas. However, there remains limited knowledge of the adaptability of typical shrubs to salinization of desert areas in arid zones. This study was conducted in a desert oasis transition zone (Tarim River, China), aiming to investigate: i) the spatial-temporal changes in soil salinity; ii) the interactions between the pedoenvironment vs typical shrub (Calligonum mongolicum). The van Genuchten soil salinity retention ensemble model (TVGSSREM-3D) was developed to simulate variations in soil water-salt transport in the desert-oasis zone and to accurately explain the main factors influencing Calligonum mongolicum desert-oases transition areas. The results showed that monthly average salinity ranged from 2.0 to 8.0 g kg−1, with a peak in August (9.17 g kg−1). The presence of human activities (Salt Drainage Canal) and the distribution of Calligonum mongolicum resulted in a clear spatial salinity zonation. Moreover, analysis of environmental indicators using the TVGSSREM-3D model revealed strong correlations between the distribution of salinity in Calligonum mongolicum desert-oases transition areas and groundwater depth (GD), minimum relative humidity (MRH), and water vapor pressure (WVP). These findings provide a scientific basis for stabilizing, restoring, and reconstructing the ecosystem of the oasis-desert transition zone.

Soil Stoichiometry Characterization in the Oasis-desert Transition Zone of Linze, Zhangye

To investigate the changes in C, N, P, and K contents and ecological stoichiometry of desert oasis soils and to elucidate their ecological responses to environmental factors, 10 sample plots were selected in the Zhangye Linze desert oasis in the middle part of the Hexi Corridor, and surface soil samples were collected to determine the C, N, P and K contents of soils and to reveal the distribution characteristics of soil nutrient contents and stoichiometric ratios in different habitats and the correlation with other environmental factors. The results showed that:① the distribution of soil carbon was uneven and heterogeneous across sites (R=0.761, P=0.06). The highest mean value was 12.85 g·kg-1 in the oasis, followed by 8.65 g·kg-1 in the transition zone and 4.1 g·kg-1 in the desert. ② The content of total soil potassium did not vary significantly and was high among deserts, transition zones, and oases and low in saline areas. ③ The mean soil C:N value was 12.92, the mean C:P value was 11.69, and the mean N:P value was 0.9, all of which were lower than the global average soil content (13.33, 72.0, and 5.9) and the Chinese soil average (12, 52.7, and 3.9). ④ Soil water content was the most influential factor affecting C, N, P, K, and ecological stoichiometry characteristics of desert oasis soils, with a contribution of 86.9%, followed by soil pH and soil porosity, with contributions of 9.2% and 3.9%, respectively. The results of this study provide basic information for the restoration and conservation of desert and oasis ecosystems and establish a basis for future study of the biodiversity maintenance mechanism in the region and its correlation with the environment.

Stem sap flow of Haloxylon ammodendron at different ages and its response to physical factors in the Minqin oasis-desert transition zone, China

Stem sap flow of Haloxylon ammodendron at different ages and its response to physical factors in the Minqin oasis-desert transition zone, China

The Effect of the Comprehensive Reform of Agricultural Water Prices on Farmers' Planting Structure in the Oasis-Desert Transition Zone-A Case Study of the Heihe River Basin.

The comprehensive reform of agricultural water prices is an important policy for promoting the high-quality sustainable development of agriculture and ensuring national water security. In this study, based on farmer survey data from different water price policy implementation areas in the oasis-desert transition zone of the Heihe River Basin (HRB), crops are divided into high-water-consuming crops and low-water-consuming crops based on the average water consumption per hm2. The content of this study consists of two main parts: first, the study explores the response of farmers to different agricultural water price policies by comparing the impact of uniform water price and tiered water price policies on their planting structure. Second, it studies the areas where the tiered water price policy is implemented to verify the impact of price signals on farmers' production decisions. The results show that, compared with the uniform water price policy, the implementation of the tiered water price policy will significantly reduce the proportion of high-water-consuming crops planted when other conditions remain unchanged. Under the tiered water price policy, the increase in water prices will reduce the proportion of farmers planting high-water-consuming crops, but the difference is not significant. This result reveals that when the opportunity cost of irrigation water increases, farmers will increase the proportion of low-water-consuming crops. The findings also indicate that a higher educational level, improved land inflow, the number of crop types, and satisfaction with the current subsidy policy will help increase the proportion of low-water-consuming crops. However, an increase in the family-cultivated land area will reduce the area of low-water-consuming crops.

Spatiotemporal Dynamics of Vegetation Index in an Oasis-Desert Transition Zone and Relationship with Environmental Factors

The oasis-desert transition zone (TZ) is an ecological buffer zone between a mobile desert and an oasis, which are important in reducing the forward mobility of sand dunes and wind and sand hazards in an oasis. In this study, the Dunhuang Oasis and its TZ in the Hexi Corridor (China) were examined. Based on the annual normalized vegetation index (NDVI) at each buffer distance of the TZ from 1987 to 2015, combing the watershed hydrology, oasis crop cultivation structure and industrial economic status, partial least squares regression models and a correlation analysis were used to examine the spatial and temporal changes in the vegetation gradient of the oasis TZ and the factors influencing those changes. (1) Spatially, the NDVI values in the TZ generally decreased gradually before stabilizing with a buffer distance (average decrease of 0.01–0.03 per 300 m). (2) Temporally, the mean values of the NDVI in the TZ show an overall wavelike variation across years. The annual average maximum NDVI value was 0.11 in 1987, whereas the annual average minimum value was 0.07 in 2014. (3) During the 1987–2015, runoff, tourist populations and water consumption for orchards were significantly and positively correlated with the NDVI; the year-end arable land area and the total industrial output value were significantly and negatively correlated with the NDVI; the rural per capita net income and water consumption for grain planting were not significantly and positively correlated with the NDVI; water consumption for the sum of vegetable and melon planting, water consumption for cotton planting, urbanization and rural populations were not significantly and negatively correlated with the NDVI. (4) The farm TZ NDVI is more strongly influenced by human activities than the undisturbed natural TZ.

Spatial pattern variation of artificial sand-binding vegetation based on UAV imagery and its influencing factors in an oasis–desert transitional zone

The spatial pattern of vegetation can reflect the impacts of the environment on plants and the response of plants to the environment, which can promote a deep understanding of the potential driving mechanisms of vegetation evolution and community maintenance. A sand-binding vegetation system without irrigation has been implemented in the oasis–desert transitional zone since the 1970 s, where the annual precipitation has been approximately 120 mm. While the mobile dunes have been effectively stabilized, a patchy pattern of sand-binding vegetation has been observed. However, we do not understand why the pattern of sand-binding vegetation changed from the initial uniform distribution to the current patchy pattern. In this study, low-altitude UAV remote sensing technology and imaging-based quantification techniques were used to explore the effects of biotic and abiotic factors on the spatial patterns of sand-binding vegetation over 50 years. The spatial pattern of Haloxylon ammodendron changed gradually from a uniform distribution to an aggregated distribution, and the degree of patch fragmentation of H. ammodendron at the landscape scale gradually increased with the age of the sand-binding vegetation. The artificial sand-binding vegetation composed of H. ammodendron showed discontinuous change in which the system state reached a transition point after 30 years and changed to another state after 40 years. There were no significant correlations between the landscape indices and soil water content in the shallow layers (0–10 cm, 10–50 cm), while the soil water content in the 50–100 cm layers was significantly negatively correlated with the class area, percentage of landscape, largest patch index, percentage of like adjacencies and aggregation index and was positively correlated with the normalized landscape shape index. The soil water content in the 100–200 cm layers was positively correlated with the number of patches and patch density. Competition intensity at the individual level had a more significant effect on the area-type indices, and competition intensity at the population level had a more significant effect on the clustering-type indices. Finally, we found that the soil water content in deep layers and competition are the main drivers of the H. ammodendron spatial pattern change from a uniform pattern to a patchy pattern. These findings enrich theory on the self-organization of vegetation in arid and semiarid environments and have important theoretical and practical significance for the establishment and management of artificial vegetation in arid areas.

新疆三种独尾草的适宜分布及其对未来气候变化的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 新疆三种独尾草的适宜分布及其对未来气候变化的响应 DOI: 10.5846/stxb202110152910 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41561007，41261011）；新疆维吾尔自治区草原总站草原生态修复治理补助项目（XJCYZZ202007） Suitable distributions of three species of Eremurus in Xinjiang and their responses to future climatic changes Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:研究国内仅分布于新疆的3种短命植物阿尔泰独尾草（Eremurus altaicus）、粗柄独尾草（Eremurus inderiensis）和异翅独尾草（Eremurus anisopterus）的适宜分布及其对未来气候的可能响应，对新疆短命植物资源的分布、利用与科学保护具有重要意义。共收集了64个自然分布点，筛选了6个气候因子和2个地形因子数据，利用MaxEnt模型和地理信息系统ArcGIS软件模拟了当前气候情景下3种独尾草的生态适宜性，探讨影响3种植物分布的主导因子及其数值范围，预测3种独尾草的适宜分布对未来气候变化（2001-2040年、2041-2080年，基于温室气体中等排放情景：SSP2-4.5共享社会经济路径）的可能响应。结果表明：（1）基准气候下，3种独尾草在新疆的适宜分布存在较大差异：阿尔泰独尾草主要分布于伊犁河谷、天山北麓、阿尔泰山中段和准噶尔西部山地；两种沙生独尾草均分布于天山中段的绿洲-荒漠区过渡带，古尔班通古特沙漠西南部沙地；（2）最干月降水量（1-25mm）主要限制了阿尔泰独尾草的适宜分布；温度季节性变动指数（1150-1672）主要限制了两种沙生独尾草的适宜分布；（3）2001-2040年和2041-2080年，3种独尾草的适宜分布整体均呈缩减趋势：阿尔泰独尾草向天山北麓和准噶尔西部山地略微缩减；粗柄独尾草和异翅独尾草向古尔班通古特沙漠南缘略微缩减。 Abstract:In China,Eremurus altaicus,Eremurus inderiensis and Eremurus anisopterus are only distributed in Xinjiang.It is of great significance to the distribution, utilization and scientific protection of ephemeral plant resources in Xinjiang to study the suitable distributions of Eremurus altaicus, Eremurus inderiensis and Eremurus anisopterus and their possible responses to future climatic changes. A total of 64 natural distribution sites, 6 climate factors and 2 topographic factors were collected in this study. MaxEnt model and ArcGIS software were used to simulate the ecological suitability of the three species of Eremurus under current climate scenario. To investigate the dominant factors influencing the distribution of the three species and their numerical ranges, and to predict the possible responses of the suitable distribution of the three species to future climatic changes (2001-2040、2041-2080,the society is a medium greenhouse gas emission scenario:based on SSP2-4.5 shard socio-economic path).The research results show that:(1) Under the basic climate, there is great differences in the suitable distribution of the three species in Xinjiang:Eremurus altaicus is mainly distributed in Ili River Valley, northern foot of the Tianshan Mountain, middle of the Altai Mountain and the Western Junggar Mountains. Both of psammophytes are distributed in the oasis-desert transition zone in the central Tianshan Mountains and the sandy land in the southwest of Gurbantunggut Desert; (2) The maximum monthly precipitation (1-25mm) mainly limited the suitable distribution of Eremurus altaicus, the temperature seasonal variation index (1150-1672) mainly limited the suitable distribution of Eremurus inderiensis and Eremurus anisopterus; (3) During 2001-2040 and 2041-2080, the suitable distribution of the three species of Eremurus show a decreasing trend as a whole:the Eremurus altaicus is reduced slightly towards the northern foot of the Tianshan Mountain and the Western Junggar Mountains; Eremurus inderiensis and Eremurus anisopterus shrink slightly towards the southern edge of the Gurbantunggut Desert. 参考文献 相似文献 引证文献

Impacts of ecological restoration projects on the ecosystem carbon storage of inland river basin in arid area, China

As an important means to cope with global climate change, ecological restoration projects have a huge impact on ecosystem carbon storage functions. Scientifically evaluating the response process and mechanism of basin ecosystem carbon storage functions in ecological restoration projects is beneficial to the improvement of regional ecosystems. Taking Shiyang River Basin (SRB) as an example, and based on the perspective of “carbon sink–carbon source” mutual transformation, the current study utilized the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model to analyze the spatio-temporal dynamics of carbon storage in SRB, quantified the effect of ecological restoration projects on the ecosystem carbon fixation capacity, and identified sensitive and vulnerable areas of carbon loss against the background of climate and land use/cover change (LUCC). The results show that the ecosystem carbon storage in SRB changed significantly before and after the ecological project implementation, with a decrease of 5.71 Tg in 1986–2000 and an increase of 14.11 Tg in 2000–2016. The proportion of carbon sink enhancement areas was only 7.46% in 1986–2000, which increased to 15.04% in 2000–2016, indicating that the ecological restoration effect of the watershed was obvious as a result of the ecological management. The contribution of LUCC brought about by the ecological restoration project to the increase in ecosystem carbon storage was as high as 103.71%, for which the increase in woodland and grassland was the key. However, in 2000–2016, low carbon optimization areas accounted for 4.17% and carbon emission control areas for 6.16% of the total area of SRB. The carbon fixation capacity of these areas declined, and carbon emissions were elevated, especially in carbon emission control areas. These were mainly distributed in the oasis–desert transition zone in the mid-lower reaches, which are sensitive and vulnerable areas for carbon loss. Therefore, in future ecological restoration and protection processes, these areas should be given more attention and protection.

Width identification of transition zone between desert and oasis based on NDVI and TCI

The oasis-desert transition zone, the boundary between the desert and oasis, has special significance in maintaining oasis stability and indicating ecosystem health. The width of the boundary is one of the critical indicators to determine the sampling design and restrict findings scaling in the study of the desert oasis transition zone. Buffer analyze and focal analyze were conducted to determine the width among oasis-desert transition zone and oasis artificial sand fixation zone in Hexi corridor China. Focal analyses indicate that TCImax and TCImin can constrain NDVI of trend variation, and the effect increases with the analysis scale. On the same spatial scale, NDVI and TCI have opposite trends and have intersections. The intersection of the sandy desert transition zone is between 30–90 m, and the oasis artificial sand-fixaion zone is between 90–150 m. The width of the sandy desert transition zone is between 220–300 m, and the width increases with the increase of analysis scale. The oasis artificial sand-fixation zone is between 420 and 540 m, which decreases with the increase of the analysis scale. NDVI shows a trend of decreasing from the oasis boundary to the desert, the trend of TCI is different from that of NDVI, showing an increase from the edge of oasis to the interior of desert. The differences in the spatial distribution of NDVI and TCI can be clearly expressed, and different types of transition zones and analysis scales have their own characteristics.

Numerical Simulations of the Impacts of Mountain on Oasis Effects in Arid Central Asia

The oases in the mountain-basin systems of Central Asia are extremely fragile. Investigating oasis effects and oasis-desert interactions is important for understanding the ecological stability of oases. However, previous studies have been performed only in oasis-desert environments and have not considered the impacts of mountains. In this study, oasis effects were explored in the context of mountain effects in the northern Tianshan Mountains (NTM) using the Weather Research and Forecasting (WRF) model. Four numerical simulations are performed. The def simulation uses the default terrestrial datasets provided by the WRF model. The mod simulation uses actual terrestrial datasets from satellite products. The non-oasis simulation is a scenario simulation in which oasis areas are replaced by desert conditions, while all other conditions are the same as the mod simulation. Finally, the non-mountain simulation is a scenario simulation in which the elevation values of all grids are set to a constant value of 300 m, while all other conditions are the same as in the mod simulation. The mod simulation agrees well with near-surface measurements of temperature, relative humidity and latent heat flux. The Tianshan Mountains exert a cooling and wetting effects in the NTM region. The oasis breeze circulation (OBC) between oases and the deserts is counteracted by the stronger background circulation. Thus, the self-supporting mechanism of oases originating from the OBC plays a limited role in maintaining the ecological stability of oases in this mountain-basin system. However, the mountain wind causes the “cold-wet’’ island effects of the oases to extend into the oasis-desert transition zone at night, which is beneficial for plants in the transition region.

Human settlement and its influencing factors during the historical period in an oasis-desert transition zone of Dunhuang, Hexi Corridor, northwest China

Many ancient cities and settlement sites have been found in Lucaogou, an ancient oasis near Dunhuang city in northwest China. These settlements indicate that humans inhabited this area during the historical period. However, the chronology and subsistence practices of this area remain unclear. Based on new data from radiocarbon dating, macrobotanical analysis, and the synthesis of historical documents and high-resolution paleoclimatic records, we discuss the inter-relationship between human settlements and plant resource utilization strategies at Lucaogou ancient oasis during historical period. Our results indicate that these ancient sites in Lucaogou area were built between the Han dynasty (202 BC-AD 220) and the Ming dynasty (AD 1368-AD 1644). People mainly used foxtail millet, broomcorn millet, barley and three types of wood (Tamarix, Salix, Populus), probably as fuel for cooking. Human settlement intensity in the area during the historical period was primarily influenced by political situations, which might also have been affected by fluctuations in precipitation.

Impact of phloem girdling on water status in desert plants Alhagi sparsifolia Shap. (Fabaceae) and Karelinia Caspica (Pall.) Less. (Asteraceae)

The removal of a ring of phloem, named girdling, is used for manipulating carbohydrate content above and below the girdle. To investigate the impact of girdling on leaf water status, an experiment was carried out in Alhagi sparsifolia Shap. and Karelinia caspica (Pall.) Less., which grew in the Cele oasis-desert transitional zone with the treatment of control, semi-girdling (SG), and full-girdling (FG). The results showed that after 30 days of girdling, stomatal conductance (Gs), transpiration rate (Tr), root carbohydrate content, root respiration rate, leaf water content and leaf water potential decreased, and leaf carbohydrate content increased under the treatment of FG in two species. On the 1st day, almost all of the treatments showed no change in these parameters, except the full-girdled leaves in A. sparsifolia, which exhibited a reduction in Gs and Tr, and an increase in midday water potential. The treatment of SG showed a similar change to FG on the 30th day in A. sparsifolia; however, in K. caspica, there was no change on the 30th day of treatment. The result of the present work indicated that girdling decreases water status over a long time. Within a short time, however, girdling decreases the Gs and Tr, which lead to an increase in leaf water status in A. sparsifolia Shap. SG also decreased leaf water status over a long time in A. sparsifolia, but not in K. caspica. Most treatments of girdling decreased leaf water status over a long time, but not within a short time. Overall, girdling affects leaf water status, but it depends on time, species, and degree of girdling.

Impact of girdling and leaf removal on Alhagi sparsifolia leaf senescence

Leaf senescence can be described as the dismantling of cellular components during the terminal stage in the development of plant organs and tissues. In order to determine the leaf senescence process when stem girdling and leaf removal both exist. An experiment was carried out in Alhagi sparsifolia, which grew in the Cele oasis-desert transitional zone with the treatment of control (CK), phloem girdling (PG), leaf removal (LR), and combined girdling and removal (GR). Some parameters related to leaf senescence were measured at the 1st and 30th day post-girdling. The results showed that after PG and GR, leaf soluble sugar content, starch content, abscisic acid content, proline content, and malondialdehyde content increased substantially and leaf photosynthetic rate, stomatal conductance, transpiration rate, photosynthetic pigment content, and water potential decreased substantially compared with CK. It also changed much more in PG leaves than in GR leaves. The change in LR leaves was opposite to that of PG and GR leaves, but the change was rather slight. The result of the present work implied that senescence of leaves treated with PG greatly accelerates, and the accumulation of carbohydrates and ABA in leaves is probably the main reason for this. Separate LR could play a role in delaying leaf senescence in plants; however, this delay effect was not obvious. Nevertheless, partial removal of leaves led to a significant compensation of girdling effects, i.e., senescence will be delayed significantly in girdled leaves when treated with partial LR.

Effects of human activities on the eco-environment in the middle Heihe River Basin based on an extended environmental Kuznets curve model

With rapid socio-economic development over the past three decades in China, adverse effects of human activities on the natural ecosystem are particularly serious in arid regions where landscape ecology is fragile due to limited water resources and considerable interannual climate variability. Data on land use, surface and ground water, climate, gross domestic product (GDP) per capita from the middle Heihe River Basin were used to (i) examine changes in water consumption, land use composition, and vegetation cover; (ii) evaluate the effectiveness of short-term management strategies for environmental protection and improvement, and (iii) apply and extend the environmental Kuznets curve (EKC) framework to describe the relationship between economic development and environmental quality in terms of the normalized difference vegetation index (NDVI). The results showed that with rapid development of agriculture and economy, land use change for the period 1986–2000 was characterized by the expansion of constructed oases, considerable contraction of oasis-desert transitional zone and natural oases. This has led to a decrease in ecosystem stability. Since 2001, effective basin management has brought about improved environment conditions, with a more optimal hierarchical structure of vegetation cover. The original EKC model could not explain most of the observed variation in NDVI (R2=0.37). Including additional climate variables, the extended EKC model to explain the observed NDVI was much improved (R2=0.78), suggesting that inclusion of biophysical factors is a necessary additional dimension in the relationship between economic development and environmental quality for arid regions with great climate variability. The relationship between GDP per capita and NDVI, with the effect of precipitation and temperature taken into consideration, was adequately described by an N-shaped curve, suggesting that the relationship between society and the environment followed a process of promotion, contradiction, and coordination.

Evapotranspiration of an oasis-desert transition zone in the middle stream of Heihe River, Northwest China

As a main component in water balance, evapotranspiration is of great importance for water saving and irrigation-measure making, especially in arid or semiarid regions. Although studies of evapotranspiration have been conducted for a long time, studies concentrated on oasis-desert transition zone are very limited. On the basis of the meteorological data and other parameters (e.g. leaf area index (LAI)) of an oasis-desert transition zone in the middle stream of Heihe River from 2005 to 2011, this paper calculated both reference (ET 0) and actual evapotranspiration (ET c) using FAO56 Penman-Monteith and Penman-Monteith models, respectively. In combination with pan evaporation (E p) measured by E601 pan evaporator, four aspects were analyzed: (1) ET 0 was firstly verified by E p; (2) Characteristics of ET 0 and ET c were compared, while the influencing factors were also analyzed; (3) Since meteorological data are often unavailable for estimating ET 0 through FAO56 Penman-Monteith model in this region, pan evaporation coefficient (K p) is very important when using observed E p to predict ET 0. Under this circumstance, an empirical formula of K p was put forward for this region; (4) Crop coefficient (K c), an important index to reflect evapotranspiration, was also analyzed. Results show that mean annual values of ET 0 and ET c were 840 and 221 mm, respectively. On the daily bases, ET 0 and ET c were 2.3 and 0.6 mm/d, respectively. The annual tendency of ET 0 and ET c was very similar, but their amplitude was obviously different. The differences among ET 0 and ET c were mainly attributed to the different meteorological variables and leaf area index. The calculated K c was about 0.25 and showed little variation during the growing season, indicating that available water (e.g. precipitation and irrigation) of about 221 mm/a was required to keep the water balance in this region. The results provide an comprehensive analysis of evapotranspiration for an oasis-desert transition zone in the middle stream of Heihe River, which was seldom reported before.

Assimilative branches and leaves of the desert plant Alhagi sparsifolia Shap. possesses a different adaptation mechanism to shade

Leaves and assimilative branches are crucial to the life cycle of Alhagi sparsifolia Shap. (Fabaceae), which grows in high-irradiance environments and is the main vegetation in the forelands of the Taklamakan Desert. This plant has an important role in wind protection and sand fixation at the oasis–desert transition zone. The morphology, physiology, and photosynthesis of A. sparsifolia leaves growing under low-light conditions have been extensively investigated. However, whether the plant's assimilative branches adapt similarly to low light levels is unclear, as are its specific light adaptation mechanisms. In this report, we characterized the biomass allocation, morphology, and chlorophyll a fluorescence of leaves and assimilative branches of A. sparsifolia. The results indicated that low-light conditions limited the normal growth of A. sparsifolia. The fraction of biomass allocated to leaves increased, whereas that to assimilative branches decreased. In addition, leaf thickness and assimilative branch diameter decreased, resulting in higher specific leaf area, specific assimilative branch length, and area for higher light absorbing and higher efficiency of light-usage. The assimilative branches and leaves were responded oppositely under low-light conditions in that leaves had lower photosystem II activity and assimilative branches had higher light-use efficiency to maximize light energy absorption for growth of A. sparsifolia.

Leaf anatomy and photosynthetic carbon metabolic characteristics in Phragmites communis in different soil water availability

To investigate the variations of anatomical and photosynthetic carbon metabolic characteristics within one species in response to increasing soil water stress, leaf anatomical characteristics, gas exchange and the activity of key enzymes in photosynthesis and photorespiration were compared in different ecotypes of Phragmitescommunis growing in an oasis-desert transitional zone (ODTZ) from swamp habitat (plot 1–3) via heavy salt meadow (plot 4–7) and light salt meadow habitat (plot 8–9) to dune habitat (plot 10–13) in Northwest China. The results showed that interveinal distance (ID) decreased with increasing water stress except that in plots of dune reed (DR). Vein mean diameter (VMD) in plot 10, 11 and 12 of the DR was significantly larger than that in other ecotypes. Leaf specific porosity (LSP) enhanced from plot 4 to plot 13 from heave salt meadow reed (HSMR) to light salt meadow reed (LSMR) and to DR. Chlorophyll fluorescence in bundle sheath cells were microscopically found in four ecotypes, especially significantly in the DR. Net CO2 assimilation rate (An) dropped rapidly from the swamp reed (SR) to the HSMR and then increased progressively from the LSMR to the DR. Stomatal conductance (gs) decreased and the water use efficiency (WUE) rose from the wet to the dry ecotypes. Sensitivity of gs to intercellular CO2 concentration (Ci) increased, but glycolate oxidase (GO) activity gradually reduced with increasing soil water deficiency. The RuBPCase activity did not reduce in four ecotypes even in DR, but, the PEPCase and NAD-ME activities as well as the ratio of PEPCase/RuBPCase were gradually enhanced with increasing soil water stress. We concluded that anatomical and photosynthetic carbon assimilating characteristics in P. communis were developing to the direction of C4 metabolism in response to the increasing drought stress in desert areas. The DR enduring severe water stress had more C4 like photosynthetic features than the HSMR and LSMR as well as SR, according to significantly increased VMD and LSP and higher gs sensitivity to Ci as well as higher PEPCase activity and lower GO activity in the DR.

Production of Perennial Vegetation in an Oasis-desert Transition Zone in NW China - Allometric Estimation, and Assessment of Flooding and Use Effects

River oases at the southern fringe of the Taklamakan desert in NW China are surrounded by belts of spontaneous vegetation that protect the oases from sand drift. As an important source of forage, fuel and construction wood, this foreland vegetation is also a component part of the agricultural system of the oases but has been, and still is, destroyed through overuse. Within a broader study that aimed to provide a basis for a sustainable management of this foreland vegetation, biomass and production were studied in four vegetation types dominated either by Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica, or Tamarix ramosissima that were thought to occur under different regimes of natural flooding in the foreland of Qira (Cele) oasis, Xinjiang, NW China. Shoot biomass components were closely correlated to basal area (Calligonum, Populus, Tamarix) or shrub volume and projection area (Alhagi), enabling non-destructive estimation of stand biomass from shoot diameters or shrub dimensions with sufficient precision using allometric regression equations. Relationships between shoot basal area and biomass of the woody species (Calligonum, Populus and Tamarix) agreed with predictions by a theoretical model of plant vascular systems, suggesting that they are determined by hydraulic and mechanical requirements for shoot architecture. Average aboveground biomass densities of typical stands in late summer were 2.97 Mg/ha in Alhagi, 3.6 Mg/ha in a row plantation and 10.9 Mg/ha in homogenous stands of Calligonum, 22–29 Mg/ha in 22 year-old Populus forests and 1.9–3.1 Mg/ha in Tamarix-dominated vegetation. Annual aboveground production including wood and assimilation organs ranged from 2.11 to 11.3 Mg/ha in plantations of Calligonum, 3.17 to 6.12 Mg/ha in Populus, and 1.55 to 1.74 Mg/ha (based on total ground area) or 3.10 to 7.15 Mg/ha (in homogenous stands) in Tamarix. Production of Alhagi is equal to peak biomass. A thinning treatment simulating use by the local population enhanced productivity of Calligonum, Populus and Tamarix. A complete harvest of Alhagi in late August decreased production in the following year. An artificial flood irrigation treatment did not sufficiently increase soil water content except in the uppermost layer and had no clear beneficial effect on growth of the four species and even a negative effect on Alhagi, which was due to increased competition from annual species. As biomass and production with or without artificial irrigation were much higher than values expected for rain-fed desert vegetation at a mean annual precipitation of 35 mm, it is concluded that the existence of all vegetation types studied is probably based on permanent access to groundwater and that natural floods or precipitation do not contribute to their water supply. The effects of agricultural groundwater use in the oasis on groundwater in the foreland of the oasis need further study. Sustainable use of this productive vegetation is possible but requires proper management.