洞庭湖洲滩土壤种子库对土壤水分变化的响应

由于三峡大坝及上游水库群的运行,长江中下游水域水文节律随之发生了改变,导致洞庭湖枯水期提前,进而影响洞庭湖洲滩植被及其土壤种子库的分布格局.本研究在洞庭湖4个自然保护区内选取共11个典型洲滩湿地,沿由水到陆方向根据植被类型将洲滩分为泥沙洲滩、泥沙—湖草洲滩过渡带、湖草洲滩、湖草—南荻洲滩过渡带、南荻洲滩5种洲滩类型.通过样带—样方法调查和采样,并结合湿润和水淹两种条件下的土壤种子库萌发实验,分析了土壤水分变化对洲滩种子库萌发特征的影响及土壤种子库与地表植被的关系.结果显示:①土壤含水量沿水到陆方向由泥沙洲滩向南荻洲滩递减;②不同类型洲滩土壤种子库密度没有显著差异;③温室萌发实验中,水淹条件下土壤种子库物种丰富度和种子库密度显著降低,东洞庭湖自然保护区土壤种子库物种丰富度和种子库密度较高;④地表植被物种丰富度高于土壤种子库,泥沙洲滩土壤种子库与地表植被物种组成的Jaccard相似性指数最低.此外,虉草(Phalaris arundinacea)、芦苇(Phragmites communis)、南荻(Miscanthus sacchariflorus)等只在地表植被中存在,而陌上菜(Lindernia procumbens)、通泉草(Mazus japonicus)等只在种子库中存在.结果表明,在进行湿地植被恢复时,不能仅依靠种子库移植技术,还要考虑湖区季节性的水位变化以及个别物种的特异性,配合有针对性的水文调控机制及相关的人工措施恢复其原有植被.     

Factors and interactions controlling infiltration,runoff, and soil loss at the microscale in a patchy Mediterranean semiarid landscape

In semiarid ecosystems, the transfer of water, sediments, and nutrients from bare to vegetated areas is known to be crucial to ecosystem functioning. Rainfall simulation experiments were performed on bare‐soil and vegetated surfaces, on both wet and dry soils, in semiarid shrub‐steppe landscapes of SE Spain to investigate the spatial and temporal factors and interactions that control the fine‐scale variation in water infiltration, runoff and soil loss, and hence the water and sediment flows in these areas. Three types of shrub‐steppe landscapes varying in plant community and physiography, and four types of plant patches (oak shrub, subshrub, tussock grass, and short grass mixed with chamaephytes) were studied. Higher infiltration and lower runoff and soil loss were measured on vegetation patches than on bare soils, for both dry and wet conditions. The oak‐shrub patches produced no runoff, while the subshrub patches showed the highest runoff and soil loss. Despite these differences among patch types, the influence of vegetation patch type on the variables analysed was not significant. The response of bare soil surfaces clearly varied between landscape types, yet the differences were only relevant under dry soil conditions. Stone cover, particularly the cover of embedded stones, and crust cover, were the key explanatory variables for the hydrological behaviour of bare soils. The study documents quantitatively how bare soils and vegetation patches function as runoff sources and runoff sinks, respectively, for a wide range of soil moisture conditions, and illustrates that landscape‐type effects on bare‐soil runoff sources may also exert an important control on the site hydrology, while the role of the vegetation patch type is less important. The effects of the control factors are modulated by antecedent soil moisture, with dry soils showing the most contrasting soil water infiltration between landscapes and surface types. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil moisture temporal stability and spatio-temporal variability about a typical subalpine ecosystem in northwestern China

Knowledge of the spatial–temporal variability of soil water content is critical for water management and restoration of vegetation in semi-arid areas. Using the temporal stability method, we investigated soil water relations and spatial–temporal variability of volumetric soil water content (VSWC) in the grassland–shrubland–forest transect at a typical semi-arid subalpine ecosystem in the Qilian Mountains, northwestern China. The VSWC was measured on 48 occasions to a depth of 70 cm at 50 locations along a 240-m transect during the 2016–2017 growing seasons. Results revealed that temporal variability in VSWC in the same soil layer in the three vegetation types and averaged across vegetation types tended to exhibit similar patterns of a decrease with increasing soil depth. Temporal stability in each vegetation type was stronger with an increase in soil depth. However, the results of temporal stability determined with standard deviation of relative difference (SDRD) disagreed with those based on the Spearman's rank correlation coefficient; the forest site had the highest Spearman rank correlation coefficient while the shrubland—the smallest SDRD in the 0–20 cm soil layer. Correlation analyses of VSWCs between two vegetation types indicated that soil water was related among all three vegetation types at the 0–20, and 0–70 cm soil layer, but in the 20–40 and 40–70 cm soil layers, significant correlation (p < .01) occurred only between adjacent vegetation types. In the upper soil layer (0–20 cm), soil water relations were mainly affected by surface runoff. In the lower soil layer (20–40 and 40–70 cm), soil water relations among the three vegetation types were highly complex, and probably resulting from a combination of root distribution and activity, interflow, and the impact of deep soil freeze–thaw dynamics. These results suggest that the factors affecting soil water are complex, and further research should address the relative importance of and interactions among different determining factors.     

Vertical variations and transport mechanism of soil moisture in response to vegetation restoration on the Loess Plateau of China

Soil moisture is essential for vegetation restoration in arid and semi-arid regions. Ascertaining the vertical distribution and transportation of soil moisture under different vegetation types has a profound effect on the ecological construction. In this study, the soil moisture at a depth of 500 cm for four typical vegetation types, including Robinia pseudoacacia, Caragana korshinskii, Stipa bungeana, and corn, were investigated and compared in the Zhifanggou watershed of the Loess plateau. Additionally, hydrogen and oxygen stable isotopes were detected to identify the transport mechanism of soil moisture. The results showed vertical distribution and transportation of soil moisture were different under different vegetation types. Depth-averaged soil moisture under S. bungeana and corn generally increased along the profile, while C. korshinskii and R. pseudoacacia showed weakly increasing and relatively stable after an obvious decreasing trend (0–40 cm). The soil moisture under R. pseudoacacia was lower than that under other vegetation types, especially in deep layer. However, the effect of R. pseudoacacia on soil moisture in the topsoil (< 30 cm) could be positive. For R. pseudoacacia (160–500 cm), C. korshinskii (0–500 cm), and S. bungeana (0–100 cm), the soil moisture declined with increased in vegetation age. Planting arbor species such as R. pseudoacacia intensified the decline of soil moisture on the Loess Plateau. The capacity of evaporation fractionation of soil moisture followed the sequence: corn > S. bungeana > R. pseudoacacia > C. korshinskii. The δ¹⁸O values in soil water fluctuated across the profile. The δ¹⁸O values changed sharply in upper layer and generally remained stable in deep layer. However, in middle layer, the vertical distribution characteristics of the δ¹⁸O values were different under different vegetation types. We estimated that piston flow was the main mode of precipitation infiltration, and the occurrence of preferential flow was related to vegetation types. These results were helpful to improve the understanding of the response of deep soil moisture to vegetation restoration and inform practices for sustainable water management.     

Breeding habitat selection by houbara bustard(Chlamydotis [undulata] macqueenii) in Mori,Xinjiang, China

The breeding habitat selection by houbara bustards in Mori, Xinjiang, China during the breeding seasons from April to June 1998–2000 was studied. Most of habitats chosen for breeding were short sub-shrubby and open areas close to high bushy patches. The nesting females clearly prefer low covered areas and avoid densely covered and high vegetation sites. The number of herb species was significantly smaller at nest sites than at randomly selected sites. Only the distance to the closest fox den contributed the most to discrimination between successful and predated nests. The average distance to the closest fox den was significantly longer at successful nests than at depredated nests. Vegetative density, plant species richness, topography and distance to the closest fox den are possibly the most important factors that determined the nest sites selection of houbara bustard. The displaying males clearly prefer low covered areas and avoid densely covered and high vegetation sites. The vegetation density and number of plant species at display sites was significantly lower than that at randomly selected sites. The average distance to the closest bushy patch was significantly shorter at display sites than at random sites. Plant species richness, vegetative density, vegetative cover and distance to the bushy patches are possibly the most important factors for the display sites selection of houbara bustard

     

Soil seed bank composition and distribution on eroded slopes in the hill‐gully Loess Plateau region (China): influence on natural vegetation colonization

On the Chinese Loess Plateau, serious slope and gully erosion have caused a decrease in soil water capacity and fertility, which has resulted in vegetation degradation and a reduction in agricultural productivity. Great efforts have been made to restore vegetation to control soil erosion, but the efficiency of artificial revegetation is not satisfactory. Natural revegetation is an alternative. However, while soil seed banks are an essential source for natural revegetation, their composition and distribution on eroded slopes remains unknown. In addition, whether or not seed loss during soil erosion limits vegetation colonization is also unknown. In this work, soil seed bank composition and distribution were studied in three situations. Specifically, three main microsites were selected as sampling plots: fish‐scale pits, as artificial deposited micro‐topography; under tussocks, as trap microsites; and open areas, as eroded areas. Soil samples were collected at depths of 0–2 cm, 2–5 cm and 5–10 cm. The soil seed bank was identified using germination experiments, and a total of 34 species were identified. The dominant species in the soil seed bank were annual/biennial herbs with an average proportion more than 90% and density reaching 19,000 seeds m^‐2. The pioneer species Artemisia scoparia was especially abundant. The dominant later successional species, such as Lespedeza davurica, Artemisia giraldii, Artemisia gmelinii, Stipa bungeana and Bothriochloa ischcemum, were present in the soil at a density that ranged from 38 to 1355 seeds m^‐2. Compared with the eroded open areas, the fish‐scale pits retained a higher density of seeds, and the tussocks retained a larger number of species. However, there was no serious reduction of the soil seed bank in the erosion areas. The present study indicates that, on these eroded slopes, the soil seed bank is not the key factor limiting the colonization of natural vegetation. Copyright © 2011 John Wiley & Sons, Ltd.     

Influences of watershed landscape composition and configuration on lake‐water quality in the Yangtze River basin of China

Lake‐water quality is highly dependent on the landscape characteristics in its respective watershed. In this study, we investigated the relationships between lake‐water quality and landscape composition and configuration within the watershed in the Yangtze River basin of China. Water quality variables, including pH, electrical conductivity (EC), dissolved oxygen (DO), Secchi depth (SD), NO₂^?, NO₃^?, NH₄⁺, TN, TP, chemical oxygen demand (COD_Mn), chlorophyll‐a (Chl‐a), and trophic state index (TSI), were collected from 16 lakes during the period of 2001–2003. Landscape composition (i.e. the percentage of vegetation, agriculture, water, urban, and bare land) and landscape configuration metrics, including number of patches (NP), patch density (PD), largest patch index (LPI), edge density (ED), mean patch area (MPA), mean shape index (MSI), contagion (CONTAG), patch cohesion index (COHESION), Shannon's diversity index (SHDI), and aggregation index (AI), were calculated for each lake's watershed. Results revealed that the percentage of agriculture was negatively related to NO₂^?, TN, TP, Chl‐a concentrations, and TSI, while the percentage of urban was significantly correlated with EC, NH₄⁺, and COD_Mn concentrations. Among landscape‐level configuration metrics, only ED showed significant relationships with TN, TP concentrations, and TSI. However, at the class level, the PD, LPI, ED, and AI of agriculture and urban land uses were significantly correlated with two or more water quality variables. This study suggests that, for a given total area, large and clustered agricultural or urban patches in the watershed may have a greater impact on lake‐water quality than small and scattered ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Characteristics and dynamics of the soil seed bank at the north edge of Taklimakan Desert

In order to understand the potential of revegetation of halophytic community at the north edge of Taklimakan Desert, the species structure, storage capacity, the vertical distribution pattern and seasonal dynamics of soil seed bank and their interrelationship with community structure of above-ground plants were investigated. The results show that (i) 9 species were identified from seed bank in different seasons indicating that plant composition in this area was simple. (ii) The seed density in soil was 222±10.79 grain/m² on average, and showed a seasonal variation range from 132±8.16 grain/m² in summer to 303±12.70 grain/m² in autumn. (iii) The similarity coefficient between soil seed bank and above-ground vegetation was 0.778. (iv) Vertically, seed densities declined with soil depth. 82.4% of total seeds were found in the top 3 cm of soil profile. No active seeds were found in soil profile below 6 cm. It is concluded that the seed bank at the north edge of Taklimakan Desert contains active seeds of all plant species observed on above ground, and is able to supply potential contribution to reconstruction of vegetation.     

A δ18O and δ2H stable water isotope analysis of subalpine forest water sources under seasonal and hydrological stress in the Canadian Rocky Mountains

Subalpine forests are hydrologically important to the function and health of mountain basins. Identifying the specific water sources and the proportions used by subalpine forests is necessary to understand potential impacts to these forests under a changing climate. The recent “Two Water Worlds” hypothesis suggests that trees can favour tightly bound soil water instead of readily available free-flowing soil water. Little is known about the specific sources of water used by subalpine trees Abies lasiocarpa (Subalpine fir) and Picea engelmannii (Engelmann spruce) in the Canadian Rocky Mountains. In this study, stable water isotope (δ¹⁸O and δ²H) samples were obtained from S. fir and Engelmann spruce trees at three points of the growing season in combination with water sources available at time of sampling (snow, vadose zone water, saturated zone water, precipitation). Using the Bayesian Mixing Model, MixSIAR, relative source water proportions were calculated. In the drought summer examined, there was a net loss of water via evapotranspiration from the system. Results highlighted the importance of tightly vadose zone, or bound soil water, to subalpine forests, providing insights of future health under sustained years of drought and net loss in summer growing seasons. This work builds upon concepts from the “Two Water Worlds” hypothesis, showing that subalpine trees can draw from different water sources depending on season and availability. In our case, water use was largely driven by a tension gradient within the soil allowing trees to utilize vadose zone water and saturated zone water at differing points of the growing season.     

澜沧江流域糯扎渡水库消落带植被的物种组成、空间分布特征及地形解释

澜沧江最大梯级水库——糯扎渡水库运行之后,消落带许多原有植被物种被淹消亡,造成大面积次生裸地以及严重水土流失现象.消落带植被亟待生态修复,但缺乏基本数据支撑和参考.2020年7月,基于轻型无人机支持下的3S技术,结合现场调研,采用神经网络模型、空间叠加分析、景观格局指数以及典型相关性分析等方法,提取了糯扎渡水库典型消落带植被分类图及地形数据,定量分析了研究区本土物种组成、面积、覆盖率、分布特征、景观空间格局及地形解释.结果显示,研究区消落带植被覆盖率达74.13%,涵盖18种植物,物种数量仅占蓄水前的18.9%,原生植物仅剩飞机草（Chromolaena odorata）存活,物种组成趋于简单,以一年生草本和多年生草本为主,分别占比55.56%、33.33%,菊科占据优势,苍耳（Xanthium sibiricum）、狗牙根（Cynodon dactylon）、牛筋草（Eleusine indica）和藿香蓟（Ageratum conyzoides）为主要优势物种,分别占比47.41%、29.39%、9.37%和4.56%,可作为生态修复备选物种.地形因子对消落带植被影响大小：高程>地表起伏度>水体距离>坡度>地形湿度指数>坡向.研究区优势植物均呈聚集分布,消落带中下部、上部分别以苍耳和狗牙根斑块为主导,苍耳和狗牙根在斑块优势度、连通性以及形状复杂性方面均远大于牛筋草和藿香蓟,表现出了较强的生存潜力.苍耳在地表起伏度0~1.26 m区段覆盖良好,狗牙根、牛筋草在地表起伏度0.78~2.07 m区段覆盖良好,当地表起伏度>2.07 m,植被生长困难.植被景观格局的破碎化程度、斑块形状复杂性分别与地表起伏度呈正相关、负相关,即地表起伏度越大导致植被景观格局越破碎和斑块形状越简单,进而导致种群生存力减弱.     

鄱阳湖湿地土壤微生物活性对年际水文变化的响应

湿地自然水文节律的改变影响着湿地生态系统的稳定与安全.为探究湿地水文变化对土壤微生物活性的影响,以鄱阳湖洲滩湿地3种典型植被狗牙根（Cynodon dactylon）、南荻（Triarrhena lutarioriparia）和苔草（Carex cinerascens）下表层土壤（0~20 cm）为研究对象,对湿地土壤微生物呼吸、微生物生物量和水解酶等土壤活性特征进行连续3年的实验监测,分析年际水位变化对不同植被湿地土壤微生物活性的影响.结果表明：丰水年显著提高土壤中养分的可利用性（有机质、总磷、速效磷）,提高土壤微生物生物量、微生物熵、水解酶活性,表明丰水年有利于湿地生态系统的物质循环转化.水文条件也能通过影响湿地植被生长改变土壤养分状况,进而对植被下土壤微生物活性产生显著影响.诸多土壤理化因子中,可溶性有机碳是驱动微生物活性变化最关键的因子.进一步分析表明,由植被类型所代表的长期水文累积效应对湿地土壤理化及微生物活性的调节作用大于单纯的年际水文变化.     

Delta size and plant patchiness as controls on channel network organization in experimental deltas

Understanding the feedbacks between water, sediment, and vegetation in deltas is an important part of understanding deltas as ecomorphodynamic systems. We conducted a set of laboratory experiments using alfalfa (Medicago sativa) as a proxy for delta vegetation to investigate: (1) the effects of plants on delta growth and channel network formation; and (2) the timescales controlling delta evolution in the presence of plants. Experiments were conducted with fluctuating discharge (i.e. flood and base flow periods) and variable seeding densities. We found that when deltas were small, channels had no memory across flood cycles, as floods could completely fill the incised channel network. When deltas were large, the larger channel volume could remain underfilled to keep channel memory. Plant patches also helped to increase the number of channels and make a more distributive network. Patchiness increased over time to continually aid in bifurcation, but as vegetation cover and patch sizes increased, patches began to merge. Larger patches blocked the flow to enhance topset deposition and channel filling, even for the case of large deltas with a high channel volume. We conclude that both plant patchiness and delta size affect the development of the channel network, and we hypothesize that their influences are manifested through two competing timescales. The first timescale, T_v, defines the time when the delta is large enough for channels to have memory (i.e. remain underfilled), and the second, T_p, defines the time when vegetation patches merge, amplifying deposition and blocking channels. When run time is between these two timescales, the delta can develop a persistent distributary network of channels aided by bifurcation around plant patches, but once T_p is reached, the channel network can again be destroyed by vegetation. © 2018 John Wiley & Sons, Ltd.     

Using stable isotopes to determine the water sources in alpine ecosystems on the east Qinghai‐Tibet plateau,China

To investigate the water circulation of eastern Qinghai‐Tibet plateau during rainy season, water samples of precipitation, throughfall, fog, soil, litter and xylem were collected for stable isotope analysis. The results showed that precipitation mainly originated as a result of the East Asian Monsoon, and the secondarily evaporated water from subalpine ecosystem was an important part in local atmospheric water cycle. The deuterium excess of rainfall in the alpine meadow was evidently higher than the precipitation in the Dengsheng stations. This suggests that a large part of precipitation in alpine meadow was derived from secondarily evaporated water and the mean contribution was 39·57%, about 3·65 mm produced shortly after rain events. Through the contrast of delta (d)‐excess value in different water samples, it could be concluded that the water in subalpine shrubland and transpiration of subalpine dark coniferous forest were the main source of secondarily evaporated water that transferred to alpine meadow. Hence, the precipitation on the east Qinghai‐Tibet plateau was doubly controlled by monsoon and local water circulation in alpine ecosystems. Copyright © 2010 John Wiley & Sons, Ltd.     

水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响

水位的洪枯变化通过江湖连通影响泛滥平原湖泊鱼类的组成和分布,因而江湖过渡带是反映泛滥平原生态系统鱼类交流和多样性变动的关键区域.尽管如此,针对江湖过渡带鱼类群落随水位洪枯变化的研究十分匮乏.本研究以菜子湖江湖过渡带为例,分别在洪水和枯水期选取包括静水和流水生境的样点对鱼类群落进行系统的调查采样,探讨水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响.共采集到鱼类6目12科37属52种,其中,洪水期和枯水期物种数差异显著,分别采集到鱼类50和42种,而静水生境和流水生境物种数差异不明显,分别采集到鱼类47和48种.与洪水期相比,枯水期山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别减少了7.3%、6.3%、14.4%和12.0%;与静水生境相比,流水生境山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别增加了5.3%、14.6%、18.0%和22.3%.SIMPER分析结果显示,麦穗鱼（Pseudorasbora parva）、蛇鮈（Saurogobio dabryi）、（Hemiculter leucisculus）、鲤（Cyprinus carpio）、鲫（Carassius auratus）、短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）、翘嘴鲌（Culter ilishaeformis）、达氏鲌（Culter dabryi）、光唇蛇鮈（Saurogobio gymnocheilus）和无须鱊（Acheilognathus gracilis）是引起水位洪枯变化以及不同生境类型鱼类群落结构差异的主要物种.优势度分析结果表明枯水期和静水生境的优势种鱼类相似,重要值较高的优势种鱼类为鲤、鲫、和似鳊;而洪水期和流水生境的优势种鱼类同样相似,重要值较高的优势种鱼类为麦穗鱼、蛇鮈、光唇蛇鮈和短颌鲚.通过双因素方差分析解析了水位洪枯变化和不同生境类型对鱼类物种和功能多样性的影响.发现洪枯水位变化仅对物种多样性指数中的物种数（Richness）产生显著差异,而对功能多样性的3个指数（功能丰富度指数（FRic）、功能离散指数（FDiv）和功能分散指数（FDis））均有显著影响.洪水期鱼类的Richness、FRic、FDiv和FDis指数均显著高于枯水期.同时,静水生境条件下的FRic指数要显著高于流水生境.本研究发现,与传统的物种多样性相比,基于功能性状的功能多样性对水位的洪枯变动更为敏感,河流周期性洪泛是泛滥平原生态系统中鱼类功能补充的重要方式.     

Forest water use in the initial stages of reclamation in the Athabasca Oil Sands Region

Following large‐scale surface oil sands mining, large tracts of the boreal forest in the Athabasca Oil Sands Region of Western Canada are legally required to be reclaimed. A greater understanding of how these novel ecosystems function and develop with regard to water use is crucial to aid in the development of regulatory practices and protocols based on information from ecosystem recovery. In this paper, a 12‐year (2003–2014) eddy covariance measurement record of latent and sensible heat fluxes and gross ecosystem productivity of carbon dioxide is analysed to evaluate how a reclaimed boreal forest has developed during its initial growth period. The study site is a reclaimed oil sands saline‐sodic clay shale overburden deposit that was topped with 100 cm of glacial till and 20 cm of peat mineral mix. The site was seeded with barley (Hordeum spp.) in 2001 to reduce erosion of the soil cover whereas aspen (Populus tremuloides Michx.) and spruce (Picea glauca [Moench] Voss) boreal tree species were planted in 2004. Changes in structure and function corresponded to the transition of dominant vegetation cover from early successional species to forest. Leaf area index increased from a growing season peak of 0.9 in 2003 to 4.0 in 2014 and was associated with an increased growing season gross ecosystem productivity (4.9 to 8.9 g C m^?2 day^?1), an increased evapotranspiration (1.6 to 3.4 mm day^?1), and a decreased partitioning of energy to sensible heat (Bowen's ratio decreased from 1.1 to 0.4). Although canopy conductance increased throughout the 12 years, the shift from early successional species to trees with more conservative water use resulted in a decrease in conductance normalized by leaf area. Water use efficiency has increased slightly since 2008 with an average of 10.0 g CO₂ kg^?1 H₂O for the last 6 years. No prolonged dry periods were observed during the study period. The functioning of this novel ecosystem is evolving as expected on the basis of the trends observed for other natural and disturbed boreal forests.     

Breeding habitat selection by houbara bustard (Chlamydotis[undulata] macqueenii) in Mori, Xinjiang, China

The breeding habitat selection by houbara bustards in Mori, Xinjiang, China duringthe breeding seasons from April to June 1998-2000 was studied. Most of habitats chosen forbreeding were short sub-shrubby and open areas close to high bushy patches. The nesting re-males clearly prefer Iow covered areas and avoid densely covered and high vegetation sites. Thenumber of herb species was significantly smaller at nest sites than at randomly selected sites.Only the distance to the closest fox den contributed the most to discrimination between successfuland predated nests. The average distance to the closest fox den was significantly longer at suc-cessful nests than at depredated nests. Vegetative density, plant species richness, topography anddistance to the closest fox den are possibly the most important factors that determined the nestsites selection of houbara bustard. The displaying males clearly prefer Iow covered areas andavoid densely covered and high vegetation sites. The vegetation density and number of plant spe-cies at display sites was significantly lower than that at randomly selected sites. The average dis-tance to the closest bushy patch was significantly shorter at display sites than at random sites.Plant species richness, vegetative density, vegetative cover and distance to the bushy patches arepossibly the most important factors for the display sites selection of houbara bustard.     

The relative contributions of alpine and subalpine ecosystems to the water balance of a mountainous,headwater catchment

Climate change is affecting the hydrology of high‐elevation mountain ecosystems, with implications for ecosystem functioning and water availability to downstream populations. We directly and continuously measured precipitation and evapotranspiration (ET) from both subalpine forest and alpine tundra portions of a single catchment, as well as discharge fluxes at the catchment outlet, to quantify the water balance of a mountainous, headwater catchment in Colorado, USA. Between 2008 and 2012, the water balance closure averaged 90% annually, and the catchment ET was the largest water output at 66% of precipitation. Alpine ET was greatest during the winter, in part because of sublimation from blowing snow, which contributed from 27% to 48% of the alpine, and 6% to 9% of the catchment water balance, respectively. The subalpine ET peaked in summer. Alpine areas generated the majority of the catchment discharge, despite covering only 31% of the catchment area. Although the average annual alpine runoff efficiency (discharge/precipitation; 40%) was greater than the subalpine runoff efficiency (19%), the subalpine runoff efficiency was more sensitive to changes in precipitation. Inter‐annual analysis of the evaporative and dryness indices revealed persistent moisture limitations at the catchment scale, although the alpine alternated between energy‐limited and water‐limited states in wet and dry years. Each ecosystem generally over‐generated discharge relative to that expected from a Budyko‐type model. The alpine and catchment water yields were relatively unaffected by annual meteorological variability, but this interpretation was dependent on the method used to quantify potential ET. Our results indicate that correctly accounting for dissimilar hydrological cycling above and below alpine treeline is critical to quantify the water balance of high‐elevation mountain catchments over periods of meteorological variability. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparing water use patterns of sand-binding species in an alpine semi-arid desert

The processes of species obtaining water resources are crucial to evaluate the adaptability of plantations, which can affect the establishment and survival of restored ecosystems and functions of water-limited ecosystems. However, there are still limitations in understanding water use patterns of different four plantations (Populus sylvestris, Salix cheliophe, Hippophae rhamnoides and Artemisia ordosica) in the Qinghai Lake basin. Stable isotopes of xylem water of four individual species were analysed at different dunes located at the eastern shore of Qinghai Lake in 2018 and 2019. The purpose of this study was to explore potential water sources used by different life form plants, to identify whether the soil moisture content and root distribution determined the plants water use patterns. Results from the Bayesian mixing model MixSIAR showed that all species mainly uses three levels of soil water, but they extracted soil water from different layers in different growing seasons among species. All species primarily depended on water from upper soil layers at the early growing stage, but P. sylvestris and S. cheliophe also absorbed much proportion middle and deep soil layers' water in dry year of 2019. All four species shift to use middle or deep soil layer water rather than shallow water in July with the most rainfall and soil water content (SWC). However, it was only used by P. sylvestris and H. rhamnoides in 2018. In all, seasonal water use pattern of different species was affected by SWC, soil texture and root distribution. Compared with moratorium plantations such as S. cheliophe, mixed afforestation of P. sylvestris and H. rhamnoides maximized of soil water sources absorbed by the plants. The study can shed light on plant–water relationships to facilitate the woody species for afforestation and desertification restoration management in the semi-arid desert ecosystem.     

Effects of Vegetation Restoration on Soil Physical Properties in the Wind–Water Erosion Region of the Northern Loess Plateau of China

In the northern Loess Plateau that has been severely affected by wind–water erosion, shifts from arable land to forest or grasslands have been promoted since 1998, using both native and introduced vegetation. However, there is little knowledge of the ecological consequences and effectiveness of the vegetation restoration in the region. Therefore, relationships between watershed‐scale soil physical properties and plant recovery processes were analyzed. The results show that soil physical properties such as bulk density, hydraulic conductivity, mean weight diameter, and the stability of >1 mm macro‐aggregates have been significantly ameliorated in the 0–20 cm soil layer under secondary natural grasslands. In contrast, re‐vegetation with introduced species such as Caragana korshinskii or Medicago sativa had adversely affected the soil physical properties, probably due to the deterioration of soil water conditions and lower organic matter inputs resulting from severe erosion. Reductions in bulk density and increases in saturated hydraulic conductivity could be used as indicators of soil structure amelioration since they are closely related to most other measured properties. Practical considerations for future re‐vegetation projects are suggested, particularly that native species with lower water consumption rates than the introduced species should be used to avoid further soil degradation.