The influence of Caragana korshinskii shrub on soil and hydrological properties in a revegetation-stabilized desert ecosystem

Abstract

Shrub-induced spatial heterogeneity of soil and hydrological properties are common in arid and semi-arid ecosystems. To examine the influence of shrubs on spatial patterns of soil physical, chemical and hydrological properties, the typical sand-fixation species, Caragana korshinskii, was studied in the Shapotou area of the Tengger Desert, China. Miniature cylinder infiltrometers were used to quantify the spatial variations of infiltration rate in the soils, and were installed at 20-cm intervals around the shrubs. Meanwhile, soil samples were collected at 0–5 cm depth every 10 cm to analyse their physical and chemical properties and soil moisture content. The results indicate that the various measured parameters showed a gradational change from sub-canopy to open space. The establishment of shrubs formed obvious “fertile islands” where more soil nutrients collected. The total nitrogen (TN), soil organic matter (SOM), electrical conductivity (EC) and surface soil moisture content decreased gradually from around shrub stems to the interspace. The sand content around shrub stems was significantly higher (p < 0.05), and decreased gradually from the centre towards the outside microsites. The silt and clay contents showed opposite variability characteristics. The variation of soil bulk density was less within 140 cm distance from the stem, and no abrupt change was found at the shrub’s drip line. No significant tendency was found for the soil pH values. The steady infiltration rates declined with increasing stem distance and then tended to be stable, and no abrupt change occurred at the position of the overhead canopy margin. The increase of infiltration rate was rapid nearer to the stem; the variability trend can be fitted by a log-log (power function) model. This study indicated the gradational change in soil and hydrological properties, which was not consistent with the binary division of shrubs into “canopy” and “interspace” zones.

Editor Z.W. Kundzewicz     

Influence of variation of soil spatial heterogeneity on vegetation restoration

Ecological restoration as a new research field of applied ecology can be traced back to the 1950s, it mainly focuses on the studies of ecological restoration of mine fields, tropical forests, wetlands and indus-try-polluted ecosystems[1-4]. Following the raising of the conception of “restoration ecology”[5], the holding of a series of international conferences and the found-ing of the International Association for Restoration Ecology, the studies of ecological restoration has be-come a quit…     

Effects of surface characteristics on infiltration patterns in an arid shrub desert

Precipitation is often the sole source of water replenishment in arid and semi‐arid areas and, thus, plays a pertinent role in sustaining desert ecosystems. Revegetation over 40 years using mainly Artemisia ordosica and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou, China, has established a dwarf‐shrub and microbiotic soil crust cover on the stabilized sand dunes. The redistribution of infiltrated moisture through percolation, root extraction, and evapotranspiration pathways was investigated. Three sets of time‐domain reflectometry (TDR) probes were inserted horizontally at 5, 10, 15, 20, 30 and 40 cm depths below the ground surface in a soil pit. The three sets of TDR probes were installed in dwarf‐shrub sites of A. ordosica and C. korshinskii community with and without a microbiotic soil crust cover, and an additional set was placed in a bare sand dune area that had neither vegetation nor a microbiotic soil crust present. Volumetric soil moisture content was recorded at hourly intervals and used in the assessment of infiltration for the different surface covers. Infiltration varied greatly, from 7·5 cm to more than 45 cm, depending upon rainfall quantity and soil surface conditions. In the shrub community area without microbiotic soil crust cover, infiltration increased due to preferential flow associated with root tunnels. The microbiotic soil crust cover had a significant negative influence on the infiltration for small rainfall events (～10 mm), restricting the infiltration depth to less than 20 cm and increasing soil moisture content just beneath the soil profile of 10 cm, whereas it was not as strong or clear for larger rainfall events (～60 mm). For small rainfall events, the wetting front depth for the three kinds of surface cover was as follows: shrub community without microbiotic soil crust > bare area > shrub community with microbiotic soil crust. In contrast, for large rainfall events, infiltration was similar in shrub communities with and without microbiotic soil crust cover, but significantly higher than measured in the bare area. Soil water extraction by roots associated with evapotranspiration restricted the wetting front penetration after 1 to 3 h of rainfall. Copyright © 2006 John Wiley & Sons, Ltd.     

Varying water utilization of Haloxylon ammodendron plantations in a desert‐oasis ecotone

Haloxylon ammodendron is a desert shrub used extensively in China for restoring degraded dry lands. An understanding of the water source used by H. ammodendron plantations is critical achieving sustainable vegetation restoration. We measured mortality, shoot size, and rooting depth in 5‐, 10‐, 20‐, and 40‐year‐old H. ammodendron plantations. We examined stable isotopic ratios of oxygen (δ¹⁸O) in precipitation, groundwater, and soil water in different soil layers and seasons, and in plant stem water to determine water sources at different shrub ages. We found that water acquisition patterns in H. ammodendron plantations differed with plantation age and season. Thus, the main water source for 5‐year‐old shrubs was shallow soil water. Water sources of 10‐year‐old shrubs shifted depending on the soil water conditions during the season. Although their tap roots could absorb deep soil water, the plantation main water sources were from soil water, and about 50% of water originated from shallow and mid soil. This pattern might occur because main water sources in these plantations were changeable over time. The 20‐ and 40‐year‐old shrubs acquired water mainly from permanent groundwater. We conclude that the main water source of a young H. ammodendron plantation was soil water recharged by precipitation. However, when roots reached sufficient depth, water originated mainly from the deep soil water, especially in the dry season. The deeply rooted 20‐ and 40‐year‐old shrubs have the ability to exploit a deep and reliable water source. To achieve sustainability in these plantations, we recommend a reduction in the initial density of H. ammodendron in the desert‐oasis ecotone to decelerate the consumption of shallow soil water during plantation establishment.     

Transpiration from three dominant shrub species in a desert‐oasis ecotone of arid regions of Northwestern China

Conservation management for the water dependent desert‐oasis ecotone in arid northwest China requires information on the water use of the dominant species. However, no studies have quantified their combined water use or linked species composition to ecotone transpiration. Here, the water use of three dominant shelterbelt shrubs (Haloxylon ammodendron, Nitraria tangutorum, and Calligonum mongolicum) within an ecotone was measured throughout the full leaf‐out period for three shrub species from 30 May to 16 October 2014, with sap flow gauges using the stem heat balance approach. Species‐specific transpiration was estimated by scaling up sap flow velocities measured in individual stems, to stand area level, using the frequency distribution of stem diameter and assuming a constant proportionality between sap flow velocity and basal cross‐sectional area for all stems. The mean peak sap flux densities (J_sn) for H. ammodendron, N. tangutorum, and C. mongolicum, were 40.12 g cm^?2 h^?1, 71.33 g cm^?2 h^?1, and 60.34 g cm^?2 h^?1, respectively, and the mean estimated daily area‐averaged transpiration rates (T_daily) for the same species were 0.56 mm day^?1, 0.34 mm day^?1, and 0.11 mm day^?1. The accumulative stand transpiration was approximately 140.8 mm throughout the measurement period, exceeding precipitation by as much as 42.1 mm. Furthermore, T_daily of these shrubs appeared to be much less sensitive to soil moisture as compared to atmospheric drivers, and the relationship between J_sn and atmospheric drivers was likely uninfluenced by soil moisture regimes in the whole profile (to 1‐m depth), especially for H. ammodendron and C. mongolicum. Results indicate that these shrubs may use deep soil water recharged by capillary rise, or may directly access shallow groundwater. This study provides quantitative data offering important implications for ecotone conservation and water and land resource management. Copyright © 2016 John Wiley & Sons, Ltd.     

Snowmelt energetics at a shrub tundra site in the western Canadian Arctic

Snow accumulation and melt were observed at shrub tundra and tundra sites in the western Canadian Arctic. End of winter snow water equivalent (SWE) was higher at the shrub tundra site than the tundra site, but lower than total winter snowfall because snow was removed by blowing snow, and a component was also lost to sublimation. Removal of snow from the shrub site was larger than expected because the shrubs were bent over and covered by snow during much of the winter. Although SWE was higher at the shrub site, the snow disappeared at a similar time at both sites, suggesting enhanced melt at the shrub site. The Canadian Land Surface Scheme (CLASS) was used to explore the processes controlling this enhanced melt. The spring‐up of the shrubs during melt had a large effect on snowmelt energetics, with similar turbulent fluxes and radiation above the canopy at both sites before shrub emergence and after the snowmelt. However, when the shrubs were emerging, conditions were considerably different at the two sites. Above the shrub canopy, outgoing shortwave radiation was reduced, outgoing longwave radiation was increased, sensible heat flux was increased and latent flux was similar to that at the tundra site. Above the snow surface at this site, incoming shortwave radiation was reduced, incoming longwave radiation was increased and sensible heat flux was decreased. These differences were caused by the lower albedo of the shrubs, shading of the snow, increased longwave emission by the shrub stems and decreased wind speed below the shrub canopy. The overall result was increased snowmelt at the shrub site. Although this article details the impact of shrubs on snow accumulation and melt, and energy exchanges, additional research is required to consider the effect of shrub proliferation on both regional hydrology and climate. Copyright 2010 John Wiley & Sons Ltd and Crown in the right of Canada.     

Soil water depletion depth by planted vegetation on the Loess Plateau

Evapotranspiration of much planted vegetation exceeds precipitation, and this can deplete soil water and cause a deep dry layer in the soil profile, which is a serious obstacle to sustainable land use on the Loess Plateau, China. This study aimed to determine water depletion depth of planted grassland, shrub, and forest in a semiarid area on the Loess Plateau. Soil moisture of five vegetation types was measured to >20 m in depth. The vegetation types were crop, natural grasse, seven-year-old planted alfalfa (Medicago sativa L.), 23-year-old planted caragana (Caragana microphylla Lam.) shrub, and 23-year-old planted pine (Pinus tabulaeformis L) forest land. Through comparing moisture of planted alfalfa grass, caragana shrub, and pine forest to crop and natural grassland, the depth and amount of soil water consumed by grassland, caragana brush and pine forest was determined. The depth of soil water depleted by alfalfa, caragana brush, and pine forest reached 15.5, 22.4 and 21.5 m, respectively. Supported by National Basic Research Program of China (Grant No. 2007CB407204) and National Natural Science Foundation of China (Grant No. 40471082)     

Seasonal changes in the water use strategies of three co‐occurring desert shrubs

Water is a major limiting factor in desert ecosystems. In order to learn how plants cope with changes in water resources over time and space, it is important to understand plant–water relations in desert region. Using the oxygen isotopic tracing method, our study clarified the seasonal changes in the water use strategies of three co‐occurring desert shrubs. During the 2012 growing season, δ¹⁸O values were measured for xylem sap, the soil water in different soil layers between 0 and 300 cm depth and groundwater. Based on the similarities in δ¹⁸O values for the soil water in each layer, three potential water sources were identified: shallow soil water, middle soil water and deep soil water. Then we calculated the percentage utilization of potential water sources by each species in each season using the linear mixing model. The results showed that the δ¹⁸O values of the three species showed a clear seasonal pattern. Reaumuria songarica used shallow soil water when shallow layer was relatively wet in spring, but mostly took up middle soil water in summer and autumn. Nitraria tangutorum mainly utilized shallow and middle soil water in spring, but mostly absorbed deep soil water in summer and autumn. Tamarix ramosissima utilized the three water sources evenly in spring and primarily relied on deep soil water in summer and autumn. R. songarica and N. tangutorum responded quickly to large rainfall pulses during droughts. Differential root systems of the three species resulted in different seasonal water use strategies when the three competed for water. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of root water uptake functions to simulate surface energy fluxes within a deep‐rooted desert shrub ecosystem

Root water uptake (RWU) is a unique process whereby plants obtain water from soil, and it is essential for plant survival. The mechanisms of RWU are well understood, but their parameterization and simulation in current Land Surface Models (LSMs) fall short of the requirements of modern hydrological and climatic modelling research. Though various RWU functions have been proposed for potential use in LSMs, none was proven to be applicable for dryland ecosystems where drought was generally the limiting factor for ecosystem functioning. This study investigates the effect of root distribution on the simulated surface energy fluxes by incorporating the observed vertical root distribution. In addition, three different RWU functions were integrated into the Common Land Model (CLM) in place of the default RWU function. A comparison of the modified model's results with the measured surface energy fluxes measured by eddy covariance techniques in a Central Asian desert shrub ecosystem showed that both RWU function and vertical root distribution were able to significantly impact turbulent fluxes. Parameterizing the root distribution based on in‐situ measurement and replacing the default RWU function with a revised version significantly improved the CLM's performance in simulating the latent and sensible heat fluxes. Sensitivity analysis showed that varying the parameter values of the revised RWU function did not significantly impact the CLM's performance, and therefore, this function is recommended for use in the CLM in Central Asian desert ecosystems and, possibly, other similar dryland ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Disposition of rainwater under creosotebush

In desert shrubland ecosystems water and nutrients are concentrated beneath shrub canopies in ‘resource islands’. Rain falling on to these islands reaches the ground as either stemflow or throughfall and then either infiltrates into the soil or runs off as overland flow. This study investigates the partitioning of rainwater between stemflow and throughfall in the first instance and between infiltration and runoff in the second. Two series of 40 rainfall simulation experiments were performed on 16 creosotebush shrubs in the Jornada Basin, New Mexico. The first series of experiments was designed to measure the surface runoff and was performed with each shrub in its growth position. The second series was designed to measure stemflow reaching the shrub base and was conducted with the shrub suspended above the ground. The experimental data show that once equilibrium is achieved, 16% of the rainfall intercepted by the canopy or 6·7% of the rain falling inside the shrub area (i.e. the area inside the shrub's circumscribing ellipse) is funnelled to the shrub base as stemflow. This redistribution of the rainfall by stemflow is a function of the ratio of canopy area (i.e. the area covered by the shrub canopy) to collar area (i.e. a circular area centred on the shrub base), with stemflow rate being positively correlated and throughfall rate being negatively correlated with this ratio. The surface runoff rate expressed as a proportion of the rate at which rainwater arrives at a point (i.e. stemflow rate plus throughfall rate) is the runoff coefficient. A multiple regression reveals that 75% of the variance in the runoff coefficient can be explained by three independent variables: the rainfall rate, the ratio of the canopy area to the collar area, and the presence or absence of subcanopy vegetation. Although the last variable is a dummy variable, it accounts for 66·4% of the variance in the runoff coefficient. This suggests that the density and extent of the subcanopy vegetation is the single most important control of the partitioning of rainwater between runoff and infiltration beneath creosotebush. Although these findings pertain to creosotebush, similar findings might be expected for other desert shrubs that generate significant stemflow and have subcanopy vegetation. Copyright © 2003 John Wiley & Sons, Ltd.     

Do biological soil crusts determine vegetation changes in sandy deserts? Implications for managing artificial vegetation

Biological soil crusts (BSCs), which are widespread in arid and semiarid regions, such as sandy deserts, strongly influence terrestrial ecosystems. Once sand‐binding vegetation has been established on sand dunes, BSCs are colonized and gradually develop from cyanobacteria dominated crusts to lichen and moss dominated crusts on dune surfaces. We conducted this study to determine if the occurrence and development of BSCs in the Tengger Desert could be used to determine sand‐binding vegetation changes via altering soil moisture and water cycling using long‐term monitoring data and field experimental observation. BSCs changed the spatiotemporal pattern of soil moisture and re‐allocation by decreasing rainfall infiltration, increasing topsoil water‐holding capacity and altering evaporation. Changes in the soil moisture pattern induced shifting of sand‐binding vegetation from xerophytic shrub communities with higher coverage (35%) to complex communities dominated by shallow‐rooted herbaceous species with low shrub coverage (9%). These results imply that BSCs can be a major factor controlling floristic and structural changes in sand‐binding vegetation and suggest that the hydrological effects of BSCs must be considered when implementing large‐scale revegetation projects in sandy deserts. Copyright © 2010 John Wiley & Sons, Ltd.     

Long-term research catchments to investigate shrub encroachment in the Sonoran and Chihuahuan deserts: Santa Rita and Jornada experimental ranges

Woody plant encroachment is a global phenomenon whereby shrubs or trees replace grasses. The hydrological consequences of this ecological shift are of broad interest in ecohydrology, yet little is known of how plant and intercanopy patch dynamics, distributions, and connectivity influence catchment-scale responses. To address this gap, we established research catchments in the Sonoran and Chihuahuan Deserts (near Green Valley, Arizona and near Las Cruces, New Mexico, respectively) that represent shrub encroachment in contrasting arid climates. Our main goals in the coordinated observations were to: (a) independently measure the components of the catchment water balance, (b) deploy sensors to quantify the spatial patterns of ecohydrological processes, (c) use novel methods for characterizing catchment properties, and (d) assess shrub encroachment impacts on ecohydrological processes through modelling studies. Datasets on meteorological variables; energy, radiation, and CO₂ fluxes; evapotranspiration; soil moisture and temperature; and runoff at various scales now extend to nearly 10 years of observations at each site, including both wet and dry periods. Here, we provide a brief overview of data collection efforts and offer suggestions for how the coordinated datasets can be exploited for ecohydrological inferences and modelling studies. Given the representative nature of the catchments, the available databases can be used to generalize findings to other catchments in desert landscapes.     

Water balance change for a re-vegetated xerophyte shrub area/Changement du bilan hydrique d’une zone replantée d’arbustes xérophiles

Abstract

Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.     

Using stable isotopes to quantify water sources for trees and shrubs in a riparian cottonwood ecosystem in flood and drought years

Riparian cottonwood forests in dry regions of western North America do not typically receive sufficient growing season precipitation to completely support their relatively high transpiration requirements. Water used in transpiration by riparian ecosystems must include alluvial groundwater or water stored in the potentially large reservoir of the unsaturated soil zone. We used the stable oxygen and hydrogen isotope composition of stem xylem water to evaluate water sources used by the dominant riparian cottonwood (Populus spp.) trees and shrubs (Shepherdia argentea and Symphoricarpos occidentalis) in Lethbridge, Alberta, during 3 years of contrasting environmental conditions. Cottonwoods did not exclusively take up alluvial groundwater but made extensive use of water sourced from the unsaturated soil zone. The oxygen and hydrogen isotope compositions of cottonwood stem water did not strongly overlap with those of alluvial groundwater, which were closely associated with the local meteoric water line. Instead, cottonwood stem water δ¹⁸O and δ²H values were located below the local meteoric water line, forming a line with a low slope that was indicative of water exposed to evaporative enrichment of heavy isotopes. In addition, cottonwood xylem water isotope compositions had negative values of deuterium excess (d‐excess) and line‐conditioned (deuterium) excess (lc‐excess), both of which provided evidence that water taken up by the cottonwoods had been exposed to fractionation during evaporation. The shrub species had lower values of d‐excess and lc‐excess than had the cottonwood trees due to shallower rooting depths, and the d‐excess values declined during the growing season, as shallow soil water that was taken up by the plants was exposed to increasing, cumulative evaporative enrichment. The apparent differences in functional rooting pattern between cottonwoods and the shrub species, strongly influenced the ratio of net photosynthesis to stomatal conductance (intrinsic water‐use efficiency), as shown by variation among species in the δ¹³C values of leaf tissue.     

Water use characteristics of coexisting sand-binding vegetation in two typical soil habitats in the desert steppe of China

Understanding the water use characteristics and water relationship of coexisting vegetation in a mixed-species plantation of trees and shrubs is crucial for the sustainable restoration of degraded arid areas. This study investigated the water use characteristic of coexisting sand-binding vegetation combinations in the sierozem habitat (Populus przewalskii Maxim namely Populus-S and Caragana liouana) and aeolian sandy soil habitats (Populus przewalskii Maxim namely Populus-A and Salix psammophila) of the desert steppe. By analysing the δ²H and δ¹⁸O isotopes in xylem, soil water, groundwater and precipitation, a Bayesian MixSIAR model was employed to quantitatively assess the water utilization characteristics of plants. Throughout the growing season, in the sierozem habitat, C. liouana exhibits the highest efficiency in utilizing soil moisture above 60 cm (53.45%) and displays adaptable water use strategies. In contrast, Populus-A predominantly relies on deep soil moisture below 60 cm plus groundwater (63.89%). In the aeolian sandy soil habitat, both Populus-A and S. psammophila similarly favour deep soil moisture below the 60 cm soil plus groundwater (66.77% and 67.60%, respectively). During the transition period from the dry to the wet seasons, although both Populus-A and S. psammophila in the aeolian sandy soil habitat shifted their water sources from deeper to shallower ones, there was considerable overlap in the water sources used by Populus-A and S. psammophila. This overlap led to competition for water resources and exacerbated the depletion of deep soil moisture in both seasons. Conversely, in the sierozem habitat, the partitioning of water sources between Populus-S and C. liouana facilitated the allocation and utilization of water resources between the two species. The findings highlight the need for species-specific consideration in water resource allocation within mixed-species plantations of trees and shrubs, which is crucial for sustainable vegetation restoration in sand-binding ecosystems.     

Assessment of the impact of different vegetation patterns on soil erosion processes on semiarid loess slopes

Soil erosion hinders the recovery and development of ecosystems in semiarid regions. Rainstorms, coupled with the absence of vegetation and improper land management, are important causes of soil erosion in such areas. Greater effort should be made to quantify the initial erosion processes and try to find better solutions for soil and water conservation. In this research, 54 rainfall simulations were performed to assess the impacts of vegetation patterns on soil erosion in a semiarid area of the Loess Plateau, China. Three rainfall intensities (15 mm h^‐1, 30 mm h^‐1 and 60 mm h^‐1) and six vegetation patterns (arbors‐shrubs‐grass ‐A‐S‐G‐, arbors‐grass‐shrubs ‐A‐G‐S‐, shrubs‐arbors‐grass ‐S‐A‐G‐, shrubs‐grass‐arbors ‐S‐G‐A‐, grass‐shrubs‐arbors ‐G‐S‐A‐ and grass‐arbors‐shrubs ‐G‐A‐S‐) were examined at different slope positions (summits, backslopes and footslopes) in the plots (33.3%, 33.3%, 33.3%), respectively. Results showed that the response of soil erosion to rainfall intensity differed under different vegetation patterns. On average, increasing rainfall intensity by 2 to 4 times induced increases of 3.1 to 12.5 times in total runoff and 6.9 to 46.4 times in total sediment yield, respectively. Moreover, if total biomass was held constant across the slope, the patterns of A‐G‐S and A‐S‐G (planting arbor at the summit position) had the highest runoff (18.34 L m^‐2 h^‐1) and soil losses (197.98 g m^‐2 h^‐1), while S‐A‐G had the lowest runoff (5.51 L m^‐2 h^‐1) and soil loss (21.77 g m^‐2 h^‐1). As indicated by redundancy analysis (RDA) and Pearson correlation results, a greater volume of vegetation located on the back‐ and footslopes acted as effective buffers to prevent runoff generation and sediment yield. Our findings indicated that adjusting vegetation position along slopes can be a crucial tool to control water erosion and benefit ecosystem restoration on the Loess Plateau and other similar regions of the world. Copyright © 2018 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.     

云贵高原湖泊夏季浮游植物组成及多样性

浮游植物是水生生态系统中重要的初级生产者,对维持水生态系统的平衡起着十分重要的作用.根据2008年云贵高原湖泊丰水期浮游植物调查数据,系统地分析了云贵高原13个湖泊中浮游植物的种群密度、生物量、组成及其多样性.云贵高原13个湖泊中共鉴定出浮游植物7门109种(绿藻52种、蓝藻23种、硅藻20种、其他14种).13个湖泊浮游植物Shannon-Wiener指数在0.5-2.2之间,其值大小与单个环境因子无显著相关.相关分析发现浮游植物总量与总氮、总磷、CODMn、硝态氮含量显著正相关,物种丰富度与总氮、总磷(0.1mg/L范围内)、CODMn含量亦显著正相关.另外,研究也发现各湖泊间浮游植物组成的相似性与各湖泊间营养状态差异显著负相关.由此可见,湖泊的营养状态不仅影响浮游植物的总量、组成以及物种丰富度,而且也影响各湖泊物种组成的相似性.