Semi-fixed Dunes Research Articles

Soil respiration dynamics in a semi-fixed sand dune under the pioneer shrub Artemisia halodendron Turcz. ex Bess. in the Horqin sandy land, northeastern China

Soil respiration is a major pathway by which carbon dioxide (CO2) fixed by terrestrial plants returns to the atmosphere. Studies of the dynamics of soil respiration in sandy land are rare and the contribution (Rc) of plant root respiration to the total soil respiration (Rt) is not well known. In this study, Rt in a semi-fixed dune planted with Artemisia halodendron was separated into autotrophic (root) respiration (Ra) and heterotrophic respiration (Rh) by the root-exclusion method. Rt and its two components were measured or calculated during 2013 on seven dates during the growing season when variation during the day was measured. Both Ra and Rh showed similar dynamics, with the maximum rates observed in July and with large daily variability observed on the earlier dates. Rc ranged from 39.3% to 53.1% during the growing season and exhibited a single peak in early August. Soil temperature at a depth of 20 cm was significantly correlated with soil respiration. Ra was more sensitive to soil temperature than Rh and the temperature sensitivity coefficients (Q10) were 3.39, 2.52, and 2.79 for Ra, Rh, and Rt, respectively. In summary, A. halodendron roots contributed an average of 46% to the total soil respiration, although this contribution varied during the growing season.

Response of soil microbial biomass and microbial entropy to desertification in desert grassland

Using an approach of spatial sequence instead of temporal succession, we investigated the variation and driving factors of soil microbial biomass and microbial entropy in desert grasslands across four different desertification stages (grassland, fixed dune, semi-fixed dune and mobile dune) in Yanchi County, Ningxia, China. The results showed that soil microbial biomass carbon, nitrogen and phosphorus reduced by 46.1%, 80.8% and 30.0% from grassland to mobile dunes, respectively. The soil microbial entropy (qMBC, qMBN, and qMBP) decreased but soil-microbial stoichiometry imbalance (C:Nimb, C:Pimb and N:Pimb) generally increased with the development of desertification. There were significantly positive relationship between soil microbial biomass nitrogen and C:Nimb, soil microbial biomass phosphorus and C:Pimb, while negative relationship between soil microbial biomass nitrogen and N:Pimb. The RDA result showed that soil ecological stoichiometry (C:N, C:P) had the strongest negative effect on soil microbial entropy carbon (qMBC). Soil microbial biomass and microbial entropy were significantly affected by desertification in desert grassland.

Responses of different herb life-history groups to a dominant shrub species along a dune stabilization gradient

Shrubs play a pivotal role in reversing desertification and in promoting ecological rehabilitation in severe environments. However, how the interactions between shrubs and their understorey species change during restoration remains unclear. Here, we report the results of an observational study conducted in the Mu Us Desert of northern China. This study explored how dune stabilization and the size of individual shrubs affect shrub–herb interactions. In particular, we aimed to determine how different life-history groups and performance indicators (e.g., biomass and richness) of subordinate species respond to shrub–herb interactions during dune stabilization. The shrub Artemisia ordosica had positive effects on understorey species in this dune system. The ability of the shrub to promote the growth of understorey species increased with dune stabilization, but decreased from small to large shrubs. This effect was due to an increase in the relative abundance and biomass of perennials and their higher sensitivity to the positive effects of the shrubs. In contrast, the ability of shrubs to improve the richness of understorey species decreased with dune stabilization, but increased from small to large shrubs. This effect occurred because perennials suffered high strain during recruitment in disturbed open patches of the semi-fixed dunes, particularly below small shrubs. Our results support the theory claiming that communities are sets of hidden interaction groups that have contrasting responses (neutral for annuals, but facilitative for perennials) to dominant neighbors in a single community, depending on their functional strategies. Furthermore, our study highlights the high efficiency of A. ordosica in facilitating ecological restoration of dry and disturbed sandy communities.

EMERGING TECHNOLOGIES IN TRANSLATIONAL PSYCHIATRY

Shrubs play a pivotal role in reversing desertification and in promoting ecological rehabilitation in severe environments. However, how the interactions between shrubs and their understorey species change during restoration remains unclear. Here, we report the results of an observational study conducted in the Mu Us Desert of northern China. This study explored how dune stabilization and the size of individual shrubs affect shrub–herb interactions. In particular, we aimed to determine how different life-history groups and performance indicators (e.g., biomass and richness) of subordinate species respond to shrub–herb interactions during dune stabilization. The shrub Artemisia ordosica had positive effects on understorey species in this dune system. The ability of the shrub to promote the growth of understorey species increased with dune stabilization, but decreased from small to large shrubs. This effect was due to an increase in the relative abundance and biomass of perennials and their higher sensitivity to the positive effects of the shrubs. In contrast, the ability of shrubs to improve the richness of understorey species decreased with dune stabilization, but increased from small to large shrubs. This effect occurred because perennials suffered high strain during recruitment in disturbed open patches of the semi-fixed dunes, particularly below small shrubs. Our results support the theory claiming that communities are sets of hidden interaction groups that have contrasting responses (neutral for annuals, but facilitative for perennials) to dominant neighbors in a single community, depending on their functional strategies. Furthermore, our study highlights the high efficiency of A. ordosica in facilitating ecological restoration of dry and disturbed sandy communities.

Characteristics of Sand Dune Pattern and Fluvial-aeolian Interaction in Horqin Sandy Land, Northeast Plain of China

The interaction between fluvial and aeolian processes can significantly change surface morphology of the Earth. Taking the Horqin Sandy Land as the research area and using Landsat series satellite remote sensing images, this study utilizes geomorphology and landscape ecology to monitor and analyze the aeolian geomorphology characteristics of the Horqin Sandy Land. Results show that the sand dunes of the Horqin Sandy Land are mainly distributed on alluvial plains along the banks of the mainstream and tributaries of the Western Liao River, and the sand dune types tend to simplify from west to east and from south to north. The aeolian geomorphology coverage tend to be decreasing in the past 40 years, with an average annual change rate of 0.31%. While the area of traveling dunes decreased, the area of fixed and semi-fixed dunes increased. The fractal dimensions of various types of sand dune have all remained relatively constant between 1.07 and 1.10, suggesting that they are experiencing a relatively stable evolutionary process. There is a complex interaction between fluvial and aeolian processes of the Horqin Sandy Land, which plays a central role in surface landscape molding. Sand dunes on both sides of different rivers on the Horqin Sandy Land present certain regularity and different characteristics in terms of morphology, developmental scale, and spatial pattern. There are six fluvial-aeolian interaction modes in this area: supply of sand sources by rivers for sand dune development, complete obstruction of dune migration by rivers, partial obstruction of dune migration by rivers, influence of river valleys on dune developmental types on both sides, influence of river valleys on dune developmental scale on both sides, and river diversion due to obstruction and forcing by sand dunes. This study deepens our understanding of the surface process mechanism of the interaction between fluvial and aeolian processes in semi-arid regions, and provides a basis for researches on regional landscape responses in the context of global environmental change.

土壤非保护性有机碳对荒漠草原沙漠化的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 土壤非保护性有机碳对荒漠草原沙漠化的响应 DOI: 10.5846/stxb201705130884 作者: 作者单位: 宁夏大学,宁夏大学 作者简介: 通讯作者: 中图分类号: 基金项目: 宁夏高等学校科学研究项目（NGY2017006） Response of unprotected soil organic carbon to desertification in desert grassland Author: Affiliation: Ningxia university,Ningxia university 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:沙化草地的恢复与重建是干旱半干旱区生态建设的重要内容，分析荒漠草原沙漠化过程中土壤非保护性有机碳分配比例的变异规律对于探讨沙化草地恢复机制具有重要的理论价值。以干旱、半干旱地区荒漠草原不同沙化阶段的土壤为研究对象，分析土壤粗颗粒有机碳、细颗粒有机碳、轻组有机碳含量和分配比例的分布特征、土壤非保护性有机碳转化为保护性有机碳的速率。结果表明：荒漠草原发生逆向演替后，土壤细颗粒有碳含量和分配比例表现为固定沙地 > 荒漠草地 > 半固定沙地 > 流动沙地；粗颗粒有机碳含量表现为荒漠草地 > 半固定沙地 > 流动沙地 > 固定沙地，粗颗粒有机碳分配比例表现为流动沙地 > 半固定沙地 > 荒漠草地 > 固定沙地；轻组有机碳含量和分配比例递减。颗粒有机碳、轻组有机碳、土壤有机碳对草地沙漠化的敏感性不同，颗粒有机碳较轻组有机碳和土壤有机碳敏感性强，其中细颗粒有机碳较粗颗粒有机碳敏感性强。随着草地沙漠化程度的增强土壤非保护性有机碳分配比例呈下降趋势，表明草地沙漠化降低土壤质量。荒漠草地退化至流动沙地土壤非保护性有机碳转化为保护性有机碳的速率整体呈上升趋势。 Abstract:The restoration and reconstruction of desertification grassland in arid and semiarid region are critical constituents of regional ecological construction. Changes of unprotected soil organic carbon in different desertification stages of desert grassland is important in discussing the mechanism of desertification grassland. The characteristics of the content and proportion of coarse particulate organic carbon (CPOC), fine particulate organic carbon (FPOC), light-fraction organic carbon (LFOC) and the rate constant for C transferring from the unprotected to the protected soil pool (k) in different desertification stages of desert grassland in arid and semiarid region were studied. The results demonstrated that during the desertification process of desert grassland, the rank of the content and proportion of FPOC was fixed dunes >grasslands > semi-fixed dunes > mobile dunes, the rank of the CPOC content was grasslands > semi-fixed dunes > mobile dunes > fixed dunes; and the rank of the CPOC proportion was mobile dunes > semi-fixed dunes > grasslands > fixed dunes. The LFOC content and proportion decreased gradually during the desertification process of desert grassland. Particulate organic carbon (POC) was more sensitive to desertification grassland than LFOC and SOC, and FPOC was more sensitive than CPOC, LFOC and SOC. The proportion of unprotected soil organic carbon decreased gradually during the desertification process in desert grassland, which indicated that there was a decrease in soil quality. The rate constant for C transferring from the unprotected to the protected soil pool (k) increased gradually during the desertification process in desert grassland (from grasslands to mobile dunes). 参考文献 相似文献 引证文献

Increased pollinator service and reduced pollen limitation in the fixed dune populations of a desert shrub

Evaluations of restoration success usually focus on the structural aspects of ecosystems. Pollination, as an important functional aspect, is often overlooked. Here, the shifts in pollinator assemblage and pollen limitation in the desert shrub Caragana microphylla were examined along a restoration gradient in Horqin Sand Land, northern China. We identified seven species of bees; however, only four bee species were found to be effective pollinators, with Xanthosaurus remota dominating in the fixed dunes, and with no bee species or only a single species, X. remota, being observed in the semi-fixed and mobile dunes. Flower visitation rate was nearly ten times higher in the fixed dunes than in the mobile and semi-fixed dunes. Experimental floral manipulations revealed that the fixed dune populations experienced less pollen limitation, along with the increase in pollinator availability. Between the mobile and semi-fixed dune populations, pollen limitation was severe and at similar levels. The intensity of pollen limitation was negatively related to pollinator abundance and richness. Overall, the dependence on pollinators for reproduction may be an important constraint that limits persistence in this system. Increased pollinator service during the restoration process may ameliorate pollen limitation, benefiting the restoration of vegetation in this semiarid sandy area.

Effects of foliage litter of a pioneer shrub (Artemisia halodendron) on germination from the soil seedbank in a semi-arid sandy grassland in China.

Vegetation recovery during succession is an important process for ecological restoration of the soil, especially in degraded sandy land. However, the driving mechanisms, such as how a pioneer species competes with other species, is uncertain. In China's Horqin Sandy Land, Artemisia halodendron is an important shrub that is common on semi-fixed dunes, where it replaces Agriophyllum squarrosum during succession, and is an important indicator species of the second stage of dune stabilization. However, how it outcompetes other species is still unclear. In this study, we conducted a seed bank germination experiment using soil from the native habitats of A. halodendron on semi-fixed dunes. We covered the soil with foliage litter of A. halodendron at a range of concentrations. Seed germination and seedling growth were strongly affected by the foliage litter. Seed germination and seedling growth were not harmed by a low concentration (≤50gm-2) of the foliage litter but severely inhibited by high concentrations (≥100gm-2). Strong allelopathy, indicated by decreased germination, increased seedling loss, and decreased plant biomass, appeared during the later stages of germination (after about 20days of incubation). Our results suggest that as a pioneer shrub during the vegetation succession that occurs during dune stabilization, A. halodendron outcompeted other species through the allelopathic effect of its foliage litter. This helps to explain the patchy distribution and heterogeneity of vegetation communities in the Horqin Sandy Land.

Relationships between Artemisia ordosica communities and environmental factors following sand-dune stabilization in the Mu Us desert, northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis (CCA) to examine the relationships between A. ordosica communities and environmental factors at three habitats: semi-fixed dune (SF), fixed dune with low-coverage biological soil crust (F), and fixed dune with high-coverage biological soil crust (FC) in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vegetation–environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0–20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.

Species composition and population structure of plant communities on semi-fixed dunes of the Gurbantongut Desert, China.

The objective of this study was to investigate species composition, and predict future development of dominant species on semi-fixed sand dunes in the Gurbantongut Desert. Using the plant height, crown area and volume instead of age structure, the growth and development condition of dominant shrub populations were analyzed. The results showed that totally 23 species were observed, of which Chenopodiaceae occurred the most with 6 genera 8 species, followed by Asteraceae with 5 genera 6 species. The vegetation community of Gurbantunggut Desert was characterized by few species, and simple structure. As a dominant species, Haloxylon persicum was distributed mainly on the top of the dunes and was a stable increasing population. However, the number of H. ammodendron was small. Artemisia ordosica, as an exotic species introduced by vegetation restoration after construction, covered mainly in the windward and the top of dunes. The po-pulation of A. ordosica had an increasing age structure with a strongly increasing potential, which has affected local species composition. The populations of Calligonum leucocladum and Ephedra distachya were lack of seedlings and had few saplings, resulting in the declining age structure. Due to the same distribution habitat, C. leucocladum might be replaced by A. ordosica in the future.

Testing Associations of Plant Functional Diversity with Carbon and Nitrogen Storage along a Restoration Gradient of Sandy Grassland.

The trait-based approach shows that ecosystem function is strongly affected by plant functional diversity as reflected by the traits of the most abundant species (community-weighted mean, CWM) and functional dispersion (FDis). Effects of CWM and FDis individually support the biomass ratio hypothesis and the niche complementarity hypothesis. However, there is little empirical evidence on the relative roles of CWM traits and FDis in explaining the carbon (C) and nitrogen (N) storage in grassland ecosystems. We measured plant functional traits in the 34 most abundant species across 24 sites along a restoration gradient of sandy grassland (mobile dune, semi-fixed dune, fixed dune, and grassland) in Horqin Sand Land, northern China. Thereafter, we calculated the CWM traits, the functional divergence of each single trait (FDvar) and the trait dispersion of multiple traits (FDis). We also measured the C and N storage in plant, litter, root, and soil. Using a stepwise multiple regression analysis, we further assessed which of the functional diversity components best explained C and N storage in the sandy grassland restoration. We found consistent links between C or N storage and leaf traits related to plant resource use strategy. However, the CWM of plant height was retained as an important predictor of C and N storage in plant, litter, soil, and total ecosystem in the final multiple models. CWMs of specific leaf area and plant height best predicted soil C and N storage and total ecosystem N storage. FDis was one of good predictors of litter C and N storage as well as total ecosystem C storage. These results suggest that ecosystem C and N pools in the sandy grassland restoration are primarily associated with the traits of the most abundant species in communities, thereby supporting the biomass ratio hypothesis. The positive associations of FDis with C storage in litter and total ecosystem provide evidence to support the niche complementarity hypothesis. Both functional traits of dominant species and traits’ dispersion in plant communities could contribute to explaining total ecosystem C storage. Thus, single- and multi-trait indices of functional composition play a crucial role in predicting C storage in sandy grasslands.

Plant functional diversity mediates the effects of vegetation and soil properties on community-level plant nitrogen use in the restoration of semiarid sandy grassland

Species-rich plant communities use nitrogen (N) more efficiently in grassland ecosystems; however, the role of plant functional diversity in affecting community level plant N-use has received little attention. We examined plant N content, stock and N-use efficiency at community-level along a restoration gradient of sandy grassland (mobile dune, semi-fixed dune, fixed dune and grassland) in Horqin Sand Land, northern China. We used the functional trait-based approach to examine how plant functional diversity, reflected by the most abundant species’ traits (community-weighted mean, CWM) and the dispersion of functional trait values (FDis), affected N-use efficiency in sandy grassland restoration. We further used the structure equation model (SEM) to evaluate the direct or indirect effects of plant species richness, biomass, functional diversity and soil properties on community-level plant N-use efficiency. We found that plant biomass and its N stock increased following sandy grassland restoration, and there were lower plant N content and higher N-use efficiency in semi-fixed dune, fixed dune and grassland as compared with mobile dune. N-use efficiency was positively associated with plant species richness, biomass, CWM plant height, CWM leaf C:N, FDis and soil gradient, but SEM results showed that species richness, CWM leaf C:N, plant biomass and FDis controlled by soil properties were the main factors exerting direct effects. CWM plant height also had a positive effect on N-use efficiency through its indirect effect on plant biomass. Soil gradient increased N-use efficiency through an indirect effect on vegetation rather than a direct effect. Final SEM models based on different plant functional diversity explained over 74% of variances in N-use efficiency. Effects of plant functional diversity on N-use efficiency supported both the mass ratio hypothesis and the complementarity hypothesis. Our results clearly highlight the important role of plant functional diversity in mediating the effects of vegetation and soil properties on community level plant N-use in sandy grassland ecosystems.

Responses of soil fungal community to the sandy grassland restoration in Horqin Sandy Land, northern China.

Sandy grassland restoration is a vital process including re-structure of soils, restoration of vegetation, and soil functioning in arid and semi-arid regions. Soil fungal community is a complex and critical component of soil functioning and ecological balance due to its roles in organic matter decomposition and nutrient cycling following sandy grassland restoration. In this study, soil fungal community and its relationship with environmental factors were examined along a habitat gradient of sandy grassland restoration: mobile dunes (MD), semi-fixed dunes (SFD), fixed dunes (FD), and grassland (G). It was found that species abundance, richness, and diversity of fungal community increased along with the sandy grassland restoration. The sequences analysis suggested that most of the fungal species (68.4 %) belonged to the phylum of Ascomycota. The three predominant fungal species were Pleospora herbarum, Wickerhamomyces anomalus, and Deconica Montana, accounting for more than one fourth of all the 38 species. Geranomyces variabilis was the subdominant species in MD, Pseudogymnoascus destructans and Mortierella alpine were the subdominant species in SFD, and P. destructans and Fungi incertae sedis were the dominant species in FD and G. The result from redundancy analysis (RDA) and stepwise regression analysis indicated that the vegetation characteristics and soil properties explain a significant proportion of the variation in the fungal community, and aboveground biomass and C:N ratio are the key factors to determine soil fungal community composition during sandy grassland restoration. It was suggested that the restoration of sandy grassland combined with vegetation and soil properties improved the soil fungal diversity. Also, the dominant species was found to be alternative following the restoration of sandy grassland ecosystems.

Soil N retention and nitrate leaching in three types of dunes in the Mu Us desert of China.

A large reservoir of soil nitrate in desert subsoil zones has been demonstrated in previous studies; however, information on the subsoil nitrate reservoir and its distribution characteristics in the deserts of China is still limited. This study investigated the distribution patterns of soil total nitrogen (N), nitrate, ammonium, and stable isotopic ratios of 15N (δ15N) in shallow (1 m) and subsoil (5 m) profiles in three types of dunes in the Mu Us desert of China. We found that soil N retention of the fixed and semi-fixed dunes followed a progressive nutrient depletion pattern in shallow soil profiles, whereas the subsoil nitrate of the fixed, semi-fixed and mobile dunes maintained a conservative accumulation pattern. The results indicate that the subsoil of the Mu Us desert may act as a reservoir of available nitrate. Furthermore, a soil δ15N analysis indicate that the nitrate content of the fixed dune is likely derived from soil nitrification, whereas the nitrate content in the mobile dune is derived from atmospheric nitrate deposition. Within the context of looming climate change and intensifying human activities, the subsoil nitrate content in the deserts of northern China could become mobilized and increase environmental risks to groundwater.

Changes in carbon and nitrogen storage along a restoration gradient in a semiarid sandy grassland

Understanding carbon (C) and nitrogen (N) pools in degraded ecosystems is useful to predict future C and N sequestration potential during restoration. Here we examined the distribution of C and N pools in plant–soil system at four successional stages: mobile dune, semi-fixed dune, fixed dune and grassland. The four stages reflect the successional sequence during sandy grassland restoration in Horqin Sandy Land, Northern China. C and N storage in plant biomass, litter and soil increased significantly with advancing sandy grassland restoration. With the conversion from mobile dune to semi-fixed dune, fixed dune and grassland, total ecosystem C and N storage increased by 1.9, 4.8, 7.1 and 3.3, 15.7, 20.6 times, respectively. More than 80% of C and N storage were stored in soil in sandy grassland restoration. C or N storage in plant and root biomass, litter and soil was positively correlated to species richness. Soil C and N storage was positively correlated to the C and N in plant and root biomass. These results suggest that sandy grassland restoration has a high potential to sequester C and N in the soil. Increasing plant production and species diversity via restoration likely enhance the C and N sequestration in sandy grassland ecosystems.

The measurement of wind erosion through field survey and remote sensing: a case study of the Mu Us Desert, China

The measurement of wind erosion is not only important to understand wind erosion itself, but also an important scientific step in efforts to reverse the process of desertification. This study develops a model that predicts sand transport flux at pixel level based on the quantitative relationship between remotely sensed vegetation coverage and observed sand transport rate data. The data were collected from field surveys in the sandy area of Yuyang County, which is located in the Mu Us Desert. The study found that the sand transport flux was 9,643 kilograms per meter annually (kga−1 m−1) for a mobile dune, 6,394 kga−1 m−1 for a semi-mobile dune, 2,634.5 kga−1 m−1 for bare cultivated land, and 127.7 kga−1 m−1 for a semi-fixed dune. Using the sand flux derived by our model, the wind erosion modulus in the Yuyang sandy area was found to be 1,673.18 tons per square kilometer annually [ta−1 (km2)−1] in 1986, 1,568.10 in 1996, and 1,685.04 in 2005. Mean vegetation coverage in the sandy area of Yuyang in 1986, 1996, and 2005 was 42.39, 48.07, and 48.03 %, respectively, indicating that overall, vegetation coverage increased in the region, while decreasing in some areas, and that the vegetation coverage incensement failed to reduce the quantity of regional wind erosion. This sand flux retrieval method has the potential for successful application in other, similar areas.

The sabulicolous therophytic associations in Sicily: new insights through the statistical approach, stressing the continuum versus discrete model of plant communities

This study presents an updated syntaxonomic review of the annual psammophilous plant communities from coastal dunes and inland territories of Sicily. A total of 301 relevés were collected. The relevés data were analysed using classification (WPGMA, similarity ratio) and ordination methods (detrended correspondence analysis and principal component analysis). Eighteen plant communities were recognized, four of which are described here for the first time (Rostrario littoreae-Tuberarietum villosissimae, Filigini asterisciflorae-Loeflingietum hispanicae, Astragalo kamarinensis-Coronilletum repandae, Sileno coloratae-Ononidetum variegatae cutandietosum maritimae). The surveyed associations are ascribed to the following orders: Cutandietalia maritimae (annual associations of semi-fixed dunes) and Malcolmietalia (inland sandy soil communities). Moreover, for this latter order, a new alliance, Filagini asterisciflorae-Linarion humilis, that groups the therophytic communities from fossil dunes and deep sandy soils of the inland of the Sicily, is proposed. Another aim of this study is to check and compare the discrete model of plant community against the continuum model along environmental gradients.

Characteristics of aeolian sediment transport over different land surfaces in northern China

Differences among regions in the meteorological, surface, and vegetation cover characteristics lead to differences in sediment transport. In this paper, field data were measured above five surface types in the arid zone of northern China to analyze the vertical distribution of sediments in the near-surface transport layer (0–50cm) and total sediment transport. We were able to express the sediment flux in this zone as an exponential function for all surface types. Sediment transport differed among the surfaces, with the greatest transport above mobile dunes, followed by cultivated land, semi-fixed dunes, fixed dunes, and a shrub community. Vegetation coverage is important for reducing wind erosion and increasing the proportion of the creep sediment transport. With increasing vegetation cover, the soil erosion decreased; the amount for the mobile dunes was 659 times that of the shrub community, and 8 times for fixed dunes. The proportion of sediment transported by creeping differed among the five surface types, with a minimum of 33% for the mobile dunes, and maximum of 44% for the shrub community.

Survival Mechanism of Psammophytes in arid desert

Species traits, environmental gradients, and distribution pattern could be three main tools providing mechanistic understanding of ecosystems, predicting the key issues in ecological stability, balance, and succession orientation. Present study is focused on a desert-oasis area, characterized by possible two abiotic environmental gradients and the distribution of seven plant species dominating four types of sand dunes. Aim of this study is to find the desert survival mechanisms for sand-binding application. Within the accessions of this transitional belt, three major types of water use characteristics could be defined. Dominant species including shrubs and herbs were significantly negatively correlated with their diurnal transpiration at rhizosphere moisture (P<0.01,R2=0.94). The results indicate pioneer species surviving arid desert by lavish water use strategies, with less cover, high Pr, high Tr, high WUE and preceding cresting of WUE. Soil property gradient played an important role in affecting the fixed and semi-fixed dunes, while soil moisture gradient was more important in shifting and semi-shifting dunes.

Scale dependence of plant species richness and vegetation-environment relationship along a gradient of dune stabilization in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still lacking. In this study, we measured the plant species richness, soil properties and altitude across four spatial scales (1, 10, 100 and 1,000 m2) at three different dune stabilization stages (mobile dune, semi-fixed dune and fixed dune) in Horqin Sandy Land, Northern China. We also examined the relationships between plant species richness, community composition and environmental factors along the gradient of dune stabilization. Our results showed that plant species richness increased with the increase of spatial scales in each dune stabilization stage, as well as with the increase of dune stabilization degrees. Canonical correspondence analysis (CCA) showed that plant distributions in the processes of dune stabilization were determined by the combined environmental gradient in relation to soil organic carbon (SOC), total nitrogen (TN), carbon/nitrogen (C/N), pH, electrical conductivity (EC), soil water content (SWC), fine sand (FS), very fine sand (VFS), silt and clay (SC), and altitude. Plant species richness was significantly and positively correlated to SOC and TN in mobile dune, and significantly and positively correlated to SOC, TN, C/N, VFS and SC in semi-fixed dune. However, no significant correlation between plant species richness and environmental factors was observed in fixed dune. In addition, plant species richness in different dune stabilization stages was also determined by the combined gradient of soil properties and altitude. These results suggest that plant species richness has obvious scale dependence along the gradient of dune stabilization. Soil resources depending on dune habitats and environmental gradients caused by dune stabilization are important factors to determine the scale dependence of species diversity in sand dune ecosystems.