Steppe Degradation Research Articles

Interaction Effects of Vegetation and Soil Factors on Microbial Communities in Alpine Steppe Under Degradation

To clarify the regulating effect of vegetation and soil factors on microbial communities in the alpine steppe under degradation on the Qinghai-Xizang Plateau, the alpine steppe in the Sanjiangyuan area of the Qinghai-Tibet Plateau was chosen. We analyzed the differences in vegetation and soil factors in different stages of degradation （non-degradation, moderate degradation, and severe degradation） and detected the variations in microbial community characteristics in the alpine steppe under different degradation stages using high-throughput sequencing technology. Eventually, redundancy analysis （RDA） and multiple regression matrixes （MRM） based on the similarity or dissimilarity matrix were used to identify key environmental factors regulating microbial （bacterial and fungal） community changes under degradation. The results showed that the degradation of the alpine steppe significantly changed the community coverage, height, biomass, and important value of graminae； significantly reduced the contents of soil organic matter, total nitrogen, total phosphorus, and silt； and increased the soil bulk density and sand content. Degradation did not change the composition of bacteria and fungi, but their composition proportions changed and also resulted in the loss of microbial richness （Chao1 index and Richness index） but did not significantly change the microbial diversity （Shannon index）. With the occurrence of degradation, the vegetation characteristics, soil physicochemical properties, and microbial diversity showed a consistent change trend. Combined with the characteristics of the network topology changes （the number of nodes and clustering coefficient significantly decreased）, it was found that degradation of the alpine steppe led to the decline of interspecies interactions, decentralization of network, and homogenization of microorganisms, but the cooperation relations among the species were maintained （positive correlation connections accounted for more than 90% in all degradation stages）. Under the alpine steppe degradation, the vegetation-soil interaction had the greatest effect on soil bacterial community, whereas soil physicochemical properties had the greatest influence on soil fungal community. Specifically, vegetation community height, biomass, and soil bulk density were the mutual factors regulating soil microorganisms, whereas the vegetation Simpson index, important value of graminae, soil total phosphorus, total potassium, and silt content were the unique factors affecting the soil bacterial community, and soil pH and total nitrogen content were the particular factors affecting the soil fungal community.

Plant species diversity and functional diversity relations in the degradation process of desert steppe in an arid area of northwest China

Species and functional diversity play a major role in the stability and sustainability of grassland ecosystems. However, changes in species and functional diversity during grassland degradation in arid areas as well as the underlying mechanisms remain unclear. In this study, we surveyed the vegetation and soil properties of arid regions across a degradation gradient to explore the shifts in species and functional diversity in plant communities, their relationships and key determinants during desert steppe degradation. Our results found significant variability in species diversity and functional diversity across degradation stages. Species diversity (Shannon-Wiener index (H), and Pielou index) and functional diversity (functional evenness (FEve) index, and Rao's quadratic entropy (RaoQ) index) tended to increase initially and then decrease with increasing grassland degradation. The Patrick index, Simpson index, functional richness (FRic) index, functional divergence (FDiv) index, and functional dispersion (FDis) index declined as grassland degradation increased. The relationships between species diversity and functional diversity indices at different stages of degradation in the desert steppe were inconsistent. From no to heavy degradation grasslands, the correlation between species diversity and functional diversity gradually weakened. Specifically, there was a significant correlation between Patrick (R) and FRic indices (R2 > 0.7) on both non-degraded and light degraded grasslands, but there was no significant correlation between R and FRic indices in moderately and heavily degraded grasslands (R2 < 0.7), and R2 gradually decreased. Redundancy analysis and partial least squares path modeling showed that grassland degradation has a significant direct effect on the species diversity and functional diversity. In addition grassland degradation has direct and indirect effects on the species diversity through soil available nitrogen, organic matter and total nitrogen. Functional diversity is directly or indirectly affected by species diversity, soil available nitrogen, organic matter and total nitrogen, soil moisture content, soil bulk density, and pH value. In summary, the relationship between species and functional diversity indices gradually weakened from areas with no degradation to heavy degradation in arid desert grasslands. Our study reveals the patterns and relationships between species diversity and functional diversity throughout the process of grassland degradation, demonstrating a gradual decrease in ecosystem stability and sustainability as degradation advances. Our results have significant implications for the restoration of grassland degradation and the management of ecosystem services in arid steppe regions.

Bacterial diversity of herbal rhizospheric soils in Ordos desert steppes under different degradation gradients

Objectives This study explored the effects of different degradation gradients on bacterial diversity in the rhizospheric soils of herb plants. Methods The alpha diversity, species composition and correlations of bacterial communities in the rhizospheric soils of herb plants were studied using metagenomics 16SrDNA gene high-throughput sequencing. Results The diversity of bacterial communities in the rhizospheric soils of herb plants differed during the degradation of desert steppes. An analysis of bacterial community alpha diversity indices showed the bacterial diversity and species evenness of rhizospheric soils were best in moderately degraded desert steppes. Among all samples, a total of 43 phyla, 133 classes, 261 orders, 421 families, 802 genera and 1,129 species were detected. At the phylum level, the predominant bacterial phyla were: Actinobacteria, Proteobacteria, Acidobacteria, Gemmatimonadetes, Chloroflexi, Planctomycetes and Bacteroidetes. At the genus level, the predominant bacterial genera were: RB41, Sphingomonas, WD2101_soil_group_unclassified, Pseudomonas and Actinomyces. The relative abundance of unknown genera was very large, which deserves further research. At the phylum and genus levels, the species abundance levels under slight and moderate degradation were significantly higher than those under extreme degradation. Correlation network diagrams showed there were many nodes in both slightly deteriorated and moderately deteriorated soils, and the node proportions were large and mostly positively correlated. These results indicate the bacterial communities in rhizospheric soils under slight or moderate deterioration are relatively stable. The rhizospheric soil microbes of desert steppes can form a stable network structure, allowing them to adequately respond to environmental conditions. Conclusions The bacterial communities in the rhizospheric soils of herb plants differ between different degradation gradients. The species number, abundance and diversity of bacterial communities in rhizospheric soils are not directly correlated with degree of degradation. The abundance, species diversity and species abundance of bacterial communities in the rhizospheric soils of moderately degraded desert steppes are the highest and most stable. The soil bacterial diversity is lowest in severely degraded desert steppes.

Arid Rangeland Degradation and Its Driving Forces in Southern Hodna, Algeria

Abstract The Algerian steppes frequently experience droughts and significant anthropogenic activities than harm its natural resources, endangering the fragile arid ecosystem’s balance. Hence, an analysis of steppe degradation can be instrumental in initiating remedial measures in the region. This study aims to assess the level of rangeland degradation in the southern Hodna region, a crucial component of the steppe landscape, and analyse the factors driving this degradation. The methodology employed a supervised classification technique, using multi-temporal remote sensing imagery from 1987 to 2016 to analyse land cover distribution. Furthermore, land cover dynamics were combined with carefully selected climatic and anthropogenic data, which were then subjected to canonical correspondece analysis to identify the primary drivers of rangeland degradation. The results reveal a sustained change in land cover dynamics, with a no table 48.65 % reduction in the rangeland class. Simultaneously, there has been a continuous expansion in sand dunes, rangeland degradation, and agriculture classes. It is worth noting that canonical correspondence analysis reveals stronger associations between rangeland degradation and anthropogenic factors than climatic factors. Finally, the study offers crucial insights into rangeland degradation in southern Hodna, aiding policymakers and land managers in developing sustainable development strategies for the region.

Short-term land degradation driven by livestock grazing does not affect soil properties in semiarid steppe rangelands

The soil–vegetation relationships are reciprocal and fundamental for terrestrial ecosystem integrity. However, the long-term degradation of vegetation cover alters edaphic conditions, which can lead to degradation of habitats, and obstructs proper ecosystem functioning. This study aimed to assess the effects of the degradation of perennial steppe vegetation due to overgrazing (i.e., continuous and free grazing) on the physicochemical characteristics and soil fertility in the steppe rangelands of Halfa (Macrochloa tenacissima syn. Stipa tenacissima) of semi-arid areas in Algeria. The edaphic parameters of the superficial horizons of degraded steppes and other undegraded steppes were compared in order to suggest adequate strategies for rangeland management and remedy the degradation of vegetation and thereby ensure the sustainability of these agro-pastoral systems. The soil, collected from the surface horizons (A1 and A2) of pedological profiles, was analyzed according to standard methods of soil physicochemical analyses to determine the particle size fractions (clay, silt, and sands), pH, electrical conductivity (EC), total and active CaCO3, organic matter (SOM), organic carbon, total nitrogen, and the C:N ratio. The distribution and variation of soil parameters between horizons and the two types of steppes were examined using generalized linear mixed models and redundancy analysis. Findings of this study revealed that the degradation of steppe vegetation cover by short-term overgrazing did not cause a significant variability in soil physicochemical parameters between degraded and undegraded steppes and the horizons A1 and A2. The sites studied have clayey–silty textures in non-degraded steppes and coarse textures dominated by sands in degraded steppes. The edaphic environment of the Halfa grass steppes was characterized by a calcareous substratum with high carbonate content (total CaCO3 = 36.8–41%, active CaCO3 = 17.5–18.5%), with an alkaline pH (8.09–8.19) and EC averaging 0.99 ± 1.24 dS/m. Soils had low SOM contents (1.42–2.93%), organic carbon (0.82–1.64%), and nitrogen (0.1–0.15%). The strong positive correlations recorded between the fine-size fractions, SOM, total CaCO3, nitrogen, and EC indicated good soil structural stability in undegraded steppes, while the negative correlations between these same variables with sand and pH substantiate the structural degradation of the soil. The negative correlation between C:N ratio and SOM indicated that the rate of SOM mineralization was rapid in semiarid steppes, with a higher fertility state in the undegraded steppe. Our findings suggest and urge to implement a restoration plan against the degradation of semi-arid Halfa steppes in order to avoid the irreversible state of soil and habitat destruction in the future because even the degradation of rangeland plant cover due to livestock overgrazing—in the short term—has not affected the edaphic characteristics of steppe rangelands.

Different remote sensing indicators reveal the transitions of two states along elevation gradients within the Xinjiang Tianshan Bogda Natural World Heritage Site

In mountainous regions, steppe degradation and desertification, which are transition processes between temperate deserts and montane steppes, are considerably affected by climate change and human disturbance. Consequently, the study of the transition ranges along the elevation gradient is particularly important for the protection, restoration, and sustainable development of natural heritage sites in arid areas. In this study, frequency analysis and the Akaike information criterion (AIC) were used to reveal the existence of two distinct potential states based on three remote sensing indicators (NDVI, normalized difference vegetation index; FVC, fractional vegetation cover; and LST, land surface temperature). The transition ranges of the two ecosystem states along altitudinal zonation were then quantitatively identified using potential energy analysis with a combination of multiple indicators. The results showed that the frequency distribution exhibited two conspicuous modes, the AIC exhibited a sharp decline from modes 1 to 2 and then remained stable with slight fluctuations from modes 2 to 5. Both features of the three indicators indicated the existence of two distinct potential states: temperate deserts and montane steppes. The two states and their transitions along the elevation gradient were detected using a potential analysis model for all three indicators. The results showed that the three indicators revealed the existence of two states, and the state with high NDVI/FVC values or low LST values began to show more attraction than the state with low NDVI/FVC values or high LST values at approximately an elevation of 1066 m. Temperate deserts below an elevation of 1060 m with montane steppes occurring above 1094 m, and two states coexisted between them. Furthermore, the distribution characteristics of local indicators of spatial association high-high, low-low, and not significant with elevation were analyzed, and the transition range (NDVI/FVC, 1040–1100 m; LST, 1040–1150 m) between different modes was consistent with those of the potential analysis, indicating the reliability of the results. This study successfully introduced the theory of multi-stable states and shifts between ecosystem states, and the potential energy analysis model into the study of natural altitudinal zones for mountainous natural world heritage sites, which will provide a scientific basis for the protection and restoration of steppe degradation in alpine regions.

Soil characteristic changes and quality evaluation of degraded desert steppe in arid windy sandy areas.

Grassland degradation has become a serious problem in some areas, making it necessary to quantitatively evaluate this process and its related factors. The study area was the arid windy sandy area in eastern Ningxia. The purpose of this study was to explore how soil properties and quality change during the process of grassland degradation in arid windy sandy areas. We looked at undegraded, lightly degraded, moderately degraded, and severely degraded desert steppe to study the physical, chemical, and biological changes at 0–5 cm, 5–15 cm, and 15–30 cm soil depths at different degradation degrees. We also analyzed the correlations across soil factors, established the minimum data set, and used the soil quality index (SQI) to evaluate the soil quality of grassland at different degradation degrees. The results showed that with grassland degradation, the soil bulk density increased; the soil clay, moisture, organic matter, total nitrogen, and available potassium content decreased; and the number of soil bacteria, actinomycetes, and fungi, as well as the activity of urease, polyphenol oxidase, protease, phosphatase, and sucrase, decreased. As soil depth increased, soil bulk density increased; the soil moisture, organic matter, available potassium, and available phosphorus content decreased; and soil microorganisms accumulated in the upper soil of undegraded, lightly, and moderately degraded grassland. There was also a positive correlation among the soil clay content, moisture content, organic matter content, total nitrogen content, available potassium content, microorganism quantity, and enzyme activity, while soil bulk density was negatively correlated with the above factors. The minimum data set for the soil quality evaluation of the degraded desert steppe was comprised of soil organic matter content, soil total nitrogen content, soil available phosphorus content, and phosphatase activity. Based on the minimum data set, we calculated the SQI of the grassland at different degradation degrees and found that the ranking based on overall soil quality was undegraded >lightly degraded >moderately degraded >severely degraded grassland. The results showed that the degradation of desert steppe in arid windy sandy areas had relatively consistent effects on the physical, chemical, and biological traits of the soil. The minimum data set can be used to replace the total data set when evaluating the soil quality of the desert steppe at different degrees of degradation.

ISSR analysis of Tulipa suaveolens (Liliaceae) populations from throughout the European part of the species range reveal genetic patterns shaped by Pleistocene transgressions of the Caspian Sea

Tulipa suaveolens Roth is a decorative bulbous, polycarpic species in the Liliaceae family. Currently, the species populations are declining due to the degradation of natural steppes. In the present article, we evaluated the genetic diversity of 216 specimens from 22 natural T. suaveolens localities in the European part of the species range using 10 inter simple sequence repeat (ISSR) markers. The polymerase chain reaction (PCR) yielded 250 unambiguous and reproducible polymorphic bands with a mean polymorphism information content (PIC) value of 0.27. Neither the principal component analysis nor the clustering method split the dataset. However, the Bayesian model‐based STRUCTURE analysis detected two genetic clusters of T. suaveolens. The analysis of the biogeographical distributional pattern of the revealed genetic groups confirmed our hypothesis that the evolution and distribution of T. suaveolens were likely affected by the Early Khvalynian transgression of the Caspian Sea and the following Enotayevsk regression. Furthermore, this hypothesis was supported by the results of the NEW HYBRIDS analysis identifying the specimens from the populations located outside the Early Khvalynian flooding limit as pure parents, while the specimens of the populations within the flooding limit were classified as backcrosses and second generation hybrids.

放牧强度对内蒙古荒漠草原土壤有机碳及其空间异质性的影响

放牧是内蒙古荒漠草原主要利用方式之一，研究不同放牧强度下土壤有机碳分布规律对退化草原恢复以及推广精准放牧技术具有重要的指导意义。基于不同放牧强度长期放牧样地（0、0.93、1.82、2.71羊单位hm^-2（a/2）^-1），采用高样本数量的取样设计并结合地统计学分析方法，研究荒漠草原土壤有机碳及其空间异质性。结果表明：中度放牧会显著降低0-30 cm土层全氮含量（P<0.05），全磷含量随放牧强度增强出现先降低后升高趋势；放牧样地土壤有机碳含量均显著低于对照样地（P<0.05），不同放牧强度处理土壤有机碳含量没有显著差异；土壤有机碳密度受放牧影响在0-20 cm土层出现显著下降（P<0.05），变化趋势同有机碳含量相似，碳氮比在重度放牧区0-10 cm土层显著降低（P<0.05）。土壤有机碳空间异质性和异质性斑块的破碎程度随放牧强度增加而增大；土壤有机碳含量与海拔高度在对照、轻度放牧和中度放牧区均呈极显著负相关（P<0.01），在重度放牧区土壤有机碳含量和海拔无显著相关性；土壤有机碳含量与土壤全氮、全磷含量均呈极显著正相关（P<0.01）。综上所述，放牧降低土壤有机碳含量，提高土壤有机碳空间异质性，土壤有机碳含量的空间变异受海拔和土壤养分含量等因素的共同影响。;Grazing is the main utilization method of desert steppe in Inner Mongolia. It is also one of the main anthropic disturbances contributing to desert steppe degradation. Studying the distribution pattern of soil organic carbon under different grazing intensity has important guiding significance for restoration of the degraded grassland and promotion of precision grazing technology. This experiment was based on long-term grazing plots with different grazing intensities (0, 0.93, 1.82, 2.71 sheep units/hm²/half year), using high-density sampling combined with geostatistics to study soil organic carbon and its spatial heterogeneity in desert steppe. The results showed that the total nitrogen content of 0-30 cm soil layer decreased significantly in moderate grazing (P<0.05), and the soil total phosphorus content firstly decreased and then increased with the increase of grazing intensity. Soil total nitrogen content decreased significantly with the deepening of soil depth in 0-30 cm soil layer of four treatments (P<0.05), but soil total phosphorus did not change significantly. Soil organic carbon content of the control plots was significantly higher than that of other treatments, and there was no significant difference in soil organic carbon content among different grazing treatments. Soil organic carbon content in every treatment decreased gradually with the deepening of the soil layer. The data distribution of organic carbon content in the four treatments was symmetrical, and the degree of data dispersion decreased with the deepening of soil layer. Soil organic carbon density decreased significantly in 0-20 cm soil layer under grazing (P<0.05), and the change trend was similar to that of organic carbon content. The C/N ratio in the 0-10 cm soil layer in heavy grazing area decreased significantly, but there was no significant change in 20-30 cm soil layer. In vertical distribution, the C/N ratio decreased significantly with the deepening of soil layer (P<0.05). The spatial heterogeneity of soil organic carbon and the degree of fragmentation of heterogeneous plaques increased with the increase of grazing intensity, but heavy grazing would change this trend, especially in moderate grazing to achieve a strong class of structural dependence. The nugget values of control and heavy grazing were higher, and the control had the largest base values among the four treatments. Elevation was negatively correlated with soil organic carbon content in control (P<0.01), lightly grazed and moderately grazed, but not with heavily grazed. Soil organic carbon content was positively correlated with soil total nitrogen content (P<0.01). Soil organic carbon content was positively correlated with soil total phosphorus content, and the correlation increased with the grazing intensity (P<0.01). In general, grazing reduced soil organic carbon content and storage, and improved spatial heterogeneity of soil organic carbon. Spatial variability of soil organic carbon content was affected by altitude and soil nutrients.

Post-Fire Vegetation Response in a Repeatedly Burned Low-Elevation Sagebrush Steppe Protected Area Provides Insights About Resilience and Invasion Resistance

Sagebrush steppe ecosystems are threatened by human land-use legacies, biological invasions, and altered fire and climate dynamics. Steppe protected areas are therefore of heightened conservation importance but are few and vulnerable to the same impacts broadly affecting sagebrush steppe. To address this problem, sagebrush steppe conservation science is increasingly emphasizing a focus on resilience to fire and resistance to non-native annual grass invasion as a decision framework. It is well-established that the positive feedback loop between fire and annual grass invasion is the driving process of most contemporary steppe degradation. We use a newly developed ordinal zero-augmented beta regression model fit to large-sample vegetation monitoring data from John Day Fossil Beds National Monument, USA, spanning 7 years to evaluate fire responses of two native perennial foundation bunchgrasses and two non-native invasive annual grasses in a repeatedly burned, historically grazed, and inherently low-resilient protected area. We structured our model hierarchically to support inferences about variation among ecological site types and over time after also accounting for growing-season water deficit, fine-scale topographic variation, and burn severity. We use a state-and-transition conceptual diagram and abundances of plants listed in ecological site reference conditions to formalize our hypothesis of fire-accelerated transition to ecologically novel annual grassland. Notably, big sagebrush (Artemisia tridentata) and other woody species were entirely removed by fire. The two perennial grasses, bluebunch wheatgrass (Pseudoroegneria spicata) and Thurber's needlegrass (Achnatherum thurberianum) exhibited fire resiliency, with no apparent trend after fire. The two annual grasses, cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae), increased in response to burn severity, most notably medusahead. Surprisingly, we found no variation in grass cover among ecological sites, suggesting fire-driven homogenization as shrubs were removed and annual grasses became dominant. We found contrasting responses among all four grass species along gradients of topography and water deficit, informative to protected-area conservation strategies. The fine-grained influence of topography was particularly important to variation in cover among species and provides a foothold for conservation in low-resilient, aridic steppe. Broadly, our study demonstrates how to operationalize resilience and resistance concepts for protected areas by integrating empirical data with conceptual and statistical models.

INFLUENCE OF REGIONAL CLIMATE CHANGE ON THE STRUCTURE AND COMPOSITION OF AGRICULTURAL LANDSCAPES OF THE SOUTHERN STEPPE OF UKRAINE

The results of scientific research on the current state of agricultural landscapes of the southern Steppe, their ploughing, physical and chemical degradation of soils and the main directions of agro technologicalevents to reduce the manifestation of these negative phenomena are presented. The latter is achieved bycreating highly productive single-species agrophytocenoses of perennial legumes and legume grass mixturesthat are resistant to regional climate change, which has been observed in the southern region in recent years.The systematic expansion of sown areas of grain and industrial crops, which are in demand on the international market, has led to an unstable state of agricultural land in the steppe zone of Ukraine, ploughingwhich at the beginning of the XXI century began to reach the highest rates in the world: Kherson region —90.2%, Kirovohrad — 86.4; Mykolaiv — 84.5; Zaporizhzhia — 84.8; Dnipropetrovsk — 84.5; Donetsk — 81.0; Odesa — 79.7%. Total in the Steppe zone — 81.2%. Established that the plowed areas significantly exceedsecologically acceptable limits, which has helped to increase rapidly the physical and chemical soil degradation, which leads to a considerable reduction of the formation of high yields of crops. The consequences of these changes were extremely unfavorable for the development of agriculture in all areas of the southern Steppe of Ukraine, which is associated with both high ploughing of agricultural landscapes, and with the violation of the structure of crops sown areas. The main direction of ensuring the reduction of physicaland chemical degradation of soils when growing crops in conditions of natural moisture is the creation of high-performance single-species agrophytocenoses of perennial legumes and multi-species legumelaced grass mixtures, resistant to extreme weather conditions that have been observed in recent years inthe southern Steppe zone.

Recognition of Landscape Key Areas in a Coal Mine Area of a Semi-Arid Steppe in China: A Case Study of Yimin Open-Pit Coal Mine

The ecological integrity and biodiversity of steppes were destroyed under the long-term and high-intensity development of open-pit coal mines in China, causing desertification, steppe degradation, landscape function defect, and so on. As a source of species maintenance and dispersal, an ecological source is a key area for preservation in order to restore the ecological security pattern of the larger landscape. The purpose of this study was to establish a landscape key area recognition model to identify the landscape key areas (LKA) surrounding an open pit coalmine located in semi-arid steppe. This study takes the Yimin open pit mining area as a case study. We assessed Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager (OLI) remote sensing images taken during the peak season of vegetation growth from July to August in 1999, 2006, 2011, and 2017. From these images, we identified the main landscape types and vegetation coverage grades in order to identify the ecological land. Next, we applied the three indices of Importance of Patch Connectivity, Habitat Quality, and Ecosystem Service Value to calculate the comprehensive results that identify ecological land. Finally, the ecological land quality results of different years are superimposed and averaged, and then Very Important Patch (VIMP), Important Patch (IMP), and General Patch (GEP) areas were used for LKA extraction. Our results showed LKA to cover 177.35 km2, accounting for 20.01% of the total study area. The landscape types identified as LKA are primarily grassland (47.37%), wetland (40.27%), and shrubland (11.88%), indicating that landscape type correlates strongly with its value as a landscape key area. The proposed landscape key area recognition model could enrich the foundations for ecological planning and ecological security pattern construction in order to support ecological protection and restoration in semi-arid steppe areas affected by coal mining.

青藏高原典型草地植被退化与土壤退化研究

PDF HTML阅读 XML下载 导出引用 引用提醒 青藏高原典型草地植被退化与土壤退化研究 DOI: 10.5846/stxb201809162019 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41771233） Different vegetation and soil degradation characteristics of a typical grassland in the Qinghai-Tibetan Plateau Author: Affiliation: Fund Project: The National Natural Science Foundation of China (General Program) 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:采用野外样方调查和室内分析法，探讨了青藏高原不同退化程度高寒草原和高寒草甸植被群落结构、植物多样性、地上-地下生物量、根系分配及土壤理化特性差异。研究表明：（1）随着退化程度加剧，高寒草原禾草优势地位未改变，高寒草甸优势种莎草逐渐被杂类草取代。（2）随着退化程度加剧，高寒草原地上生物量显著降低（P<0.05），高寒草甸地上生物量先保持稳定再下降。高寒草甸地下生物量较高寒草原地下生物量对退化响应更敏感。（3）高寒草原退化过程中，莎草地上物生量变化不明显（P>0.05），禾草地上生物量贡献率由88.12%减少至53.54%，杂类草地上生物量贡献率由0.08%增加至42.81%；高寒草甸退化过程中，禾草和杂类草地上生物量先增加后减小，莎草地上生物量占比由69.15%减少至0.04%，杂类草地上生物量占比由12.56%增加至92.61%。（4）随着退化程度加剧，高寒草原根系向浅层迁移，高寒草甸根系向深层迁移。（5）退化对高寒草甸土壤含水量（θ）、土壤有机碳（SOC）、总氮（TN）及土壤容重（BD）影响均比高寒草原更强烈。本研究对青藏高原退化草地恢复治理具有重要的参考价值。 Abstract:This study used a field sampling survey and laboratory analysis to investigate the different characteristics of community structure, above/belowground biomass, plant composition and diversity, root proportions in different soil layers, and soil physiochemical properties between alpine steppes and alpine meadows in the Qinghai-Tibetan Plateau. Five degradation stages were identified including non-degradation (ND), light degradation (LD), moderate degradation (MD), severe degradation (SD), and extreme degradation (ED). The results are as follows:(1) as degradation level increased, graminoid dominance in alpine steppes remained unchanged, but sedges in alpine meadows were gradually replaced by the subdominant forb species. (2) With increased alpine steppe degradation, there was a significant decrease in aboveground biomass (P<0.05). The grassland degradation did not affect significantly aboveground biomass with the exception of ED alpine meadows (P<0.05). The response of underground biomass to degradation in alpine meadows was more sensitive compared with alpine steppes. (3) The aboveground sedge biomass exhibited invisible trends with the increase of alpine steppe degradation. The proportion of aboveground graminoid biomass decreased from 88.12% (ND) to 53.54% (ED), while that of forbs increased from 0.08% (ND) to 42.81% (ED). In the process of the ecological succession of alpine meadow degradation, the aboveground graminoid and forb biomass significantly increased except a decrease in ED areas. The contribution of aboveground sedge biomass decreased from 69.15% (ND) to 0.04% (ED), while that of forbs increased from 12.56% (ND) to 92.61% (ED). (4) The alpine steppe root systems showed the increased shallowness as degradation levels increased. However, the alpine meadows showed an opposite trend. (5) The study determined that soil water content (θ), soil organic carbon (SOC), total nitrogen (TN), and bulk density (BD) of alpine meadows were more intensively influenced by degradation compared to those of alpine steppes. The results could provide a valuable reference for the restoration of the degraded grassland in the Qinghai-Tibetan Plateau. 参考文献 相似文献 引证文献

Hepatic transcriptome profile of sheep (Ovis aries) in response to overgrazing: novel genes and pathways revealed

BackgroundOvergrazing is a major factor that causes steppe degradation in Inner Mongolian, resulting in extensive ecosystem damage. Scarcity of grass means sheep are smaller and therefore mutton and cashmere production is greatly reduced, which has resulted in massive annual economic losses. Liver is the primary metabolic organ in mammals. It is also the key source of energy supply and detoxification of metabolites in animals, has a close relationship with animal growth. However, investigations on the responses of sheep induced by consequence of overgrazing, particularly those relating to liver-related molecular mechanisms and related metabolic pathways, remain elusive.ResultsThe body weight daily gain of sheep, immune organ indices (liver and spleen), and serum parameters related to immune response, protein synthesis and energy supply (IgG, albumin, glucose and non-esterified fatty acid) were significantly lower in the overgrazing group. Other serum parameters including alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, blood urea nitrogen and interleukin-6 were significantly higher in the overgrazing group. For the RNA-Seq results, we identified approximately 50 differentially expressed genes, of which half of were up-regulated and the other half were down-regulated (overgrazing group versus light grazing group). Bioinformatics analysis identified two enriched KEGG pathways including peroxisome proliferator-activated receptor (PPAR) signaling pathway (related to lipolysis) and ECM-receptor interaction (related to liver injury and apoptosis). Additionally, several of the down-regulated genes were related to detoxification and immune response.ConclusionsOverall, based on the high-throughput RNA sequencing profile integrated with the results of serum biochemical analyses, consequences of lower forage availability and quality under overgrazing condition induced altered expression levels of genes participating in energy metabolism (particularly lipid metabolism) and detoxification and immune responses, causing lipolysis and impaired health status, which might be key reasons for the reduced growth performance of sheep. This investigation provides a novel foundation for the development of sheep hepatic gene interactive networks that are a response to the degraded forage availability under overgrazing condition.

Changes in the soil microbial communities of alpine steppe at Qinghai-Tibetan Plateau under different degradation levels

The alpine steppe at Qinghai-Tibetan Plateau is an important area for conserving water source and grassland productivity; however, knowledge about the microbial community structure and function and the risk to human health due to alpine plant-soil ecosystems is limited. Thus, we used prediction methods, such as Tax4Fun, and performed a metagenome pre-study using 16S rRNA sequencing reads for a small scale survey of the microbial communities at degraded alpine steppes (i.e., non-degraded (ND), lightly degraded (LD), moderately degraded (MD), heavily degraded (HD), and extremely degraded (ED) steppes) by Illumina high-throughput sequencing technology. Although there were no significant differences in the microbial alpha diversity among the different degraded alpine steppes and the dominant phyla at the different degraded alpine steppes, including Actinobacteria, Proteobacterial, Acidobacteria and Chloroflexi, were similar, the beta-diversity significantly differed, indicating that alpine steppe degradation might result in variation in microbial community compositions. The linear discriminate analysis (LDA) effect size (LEfSe) analysis found twenty-one biomarkers, most of which belonged to Actinobacteria, suggesting that microbes with a special function (such as the decomposition soil organic matter) might survive in alpine steppes. In addition, the functional profiles of the bacterial populations revealed an association with many human diseases, including infectious diseases. In addition, the microbial communities were mainly correlated with the populations of Gramineae and soil total phosphorous. These results suggested that alpine steppe degradation could result in variations in the microbial community composition, structure and function at Qinghai-Tibetan Plateau. Further studies investigating the degraded alpine steppe environment are needed to isolate these potential pathogenic microbes and help protect livestock using these alpine steppes.

The spatial distribution and accumulation characteristics of heavy metals in steppe soils around three mining areas in Xilinhot in Inner Mongolia, China

Metal deposition has become a major environmental problem in China due to its adverse effects on human and ecosystem health, particularly in Inner Mongolia, where frequent dust storms (due to steppe degradation and desertification) and soil pollution (associated with the increasing mining activities) have occurred in recent decades. To assess spatial distribution of heavy metals and the influences of mining activities on geochemical behavior of heavy metals in soils, soil samples with depth of 0-10, 10-20, and 20-30cm at each site were collected from different directions in the vicinity of three mines (coal mine, gold mine, and fluorite mine) in a typical steppe zone of Inner Mongolia, China. Six elements (Cd, Pb, Zn, Cr, Cu, and Ni) in the soils were analyzed using inductively coupled plasma emission spectrometer (ICP-OES). The results indicated that the average concentrations of Cd, Pb, Zn, Cr, Cu, and Ni in the soil of the study area around three mines were lower than the second class level of the National Soil Environment Safety Standard, but mostly were higher than the background value of soil in the Inner Mongolia. Northwest, southwest, and northeast wind directions have a great influence on the distribution of metals in coal, gold, and fluorite mine area, respectively. The concentration of heavy metals in coal, gold, and fluorite increased with the distance from the center of the mine, then reached a peak, then decreased gradually. The vertical mobility of metals in soil profiles was slightly significant for Cd>Cr>Zn>Ni in coal mine area and was not significant in gold and fluorite mines. Multivariate statistical methods such as principal component analysis and cluster analysis, coupled with correlation coefficient analysis, showed that Cd, Cu, Cr, and Ni in the mining area came from the same source, while Zn and Pb came from the other source. That the sources of heavy metals in the mining area were discussed would not only enhance our knowledge regarding the soil pollution status in the study area but would also provide us information to manage the sources of these elements in the study area.

Microbial Nitrogen-Cycle Gene Abundance in Soil of Cropland Abandoned for Different Periods.

In Inner Mongolia, steppe grasslands face desertification or degradation because of human overuse and abandonment after inappropriate agricultural management. The soils in these abandoned croplands exist in heterogeneous environments characterized by widely fluctuating microbial growth. Quantitative polymerase chain reaction analysis of microbial genes encoding proteins involved in the nitrogen cycle was used to study Azotobacter species, nitrifiers, and denitrifiers in the soils from steppe grasslands and croplands abandoned for 2, 6, and 26 years. Except for nitrifying archaea and nitrous oxide-reducing bacteria, the relative genotypic abundance of microbial communities involved in nitrogen metabolism differed by approximately 2- to 10-fold between abandoned cropland and steppe grassland soils. Although nitrogen-cycle gene abundances varied with abandonment time, the abundance patterns of nitrogen-cycle genes separated distinctly into abandoned cropland versus light-grazing steppe grassland, despite the lack of any cultivation for over a quarter-century. Plant biomass and plant diversity exerted a significant effect on the abundance of microbial communities that mediate the nitrogen cycle (P < 0.002 and P < 0.03, respectively). The present study elucidates the ecology of bacteria that mediate the nitrogen cycle in recently abandoned croplands.

Effects of habitat alteration on lizard community and food web structure in a desert steppe ecosystem

Habitat alteration has major impacts on biodiversity, but we do not fully understand how changes in vegetation structure alter community interactions among vertebrate predators and their prey. Desertification is a major threat to degraded steppe habitats, prompting re-vegetation efforts to slow wind erosion. These processes alter both the structure and composition of the vegetation, and thus could influence predator and prey abundances, and their interactions. We investigated how habitat structure (degraded [sparse], natural [intermediate], or re-vegetated [dense]) influences lizard species richness, abundance, and diversity, and the interactions between these predators and invertebrate prey in the arid desert steppe. Structurally sparse and dense vegetation supported higher lizard abundances than natural habitats, with Phrynocephalus frontalis and Eremias argus dominating sparse and dense habitats respectively, and P. frontalis and E. multiocellata co-dominating natural habitats. Habitats that were structurally dense also supported the most complex trophic interactions among predators and prey, whereas structurally sparse habitats had low interaction diversity and interaction evenness, with most energy flowing along few trophic pathways. Steppe degradation therefore simplifies community trophic interactions, and restoration through enhanced protection of natural steppe habitat structure may play an important role in the conservation of healthy predator–prey communities. Desertification is a pressing issue throughout most of the arid steppe; revegetation efforts resulted in robust communities, in addition to promoting persistence of E. argus, which is endemic and threatened. Maintaining a heterogenous structural landscape thus may be the most promising way to combat desertification while at the same time restoring predator–prey community composition.

Simulation of soil nitrogen storage of the typical steppe with the DNDC model: A case study in Inner Mongolia, China

Soil nutrient depletion is one of the characteristics of steppe degradation. Soil nitrogen (N) storage is an indicator of ecosystem productivity, and its simulation is necessary to monitor steppe degradation and for recovery measures. The study presents a simulation framework of soil N storage by integrating a denitrification–decomposition (DNDC) ecosystem model-based simulation and multi-source remote sensing data-based inversion. The DNDC model is a key player in the framework, whereas remote sensing prepares the input parameters and verification data. To run a DNDC model spatially, climate, soil, and vegetation databases were built, and land use, slop, grazing, and mowing parameters were formulated by remote sensing inversion. A soil N storage prediction model was established with the maximum of normalized difference vegetation index (NDVI) to provide comparable results with the simulation of soil N storage with the DNDC model. The results indicate that soil N storage declined from east to west throughout the study area. From 1990 to 2011, no change in the spatial distribution of soil N storage was determined, and the spatial heterogeneity of soil N storage decreased with its increase in the low-N area and decrease in the high-N area. A significant correlation (P<0.01) was determined between soil N storage data detected by remote sensing inversion and that simulated with DNDC, and both estimation results of soil N storage matched well. Soil N storage simulated with the DNDC model was more sensitive to soil organic carbon (SOC), bulk density, pH and N fixation index than other parameters, and using the most sensitive factor (MSF) method, the range of annual mean soil N storage was determined to be between 2339.61 and 5484.61kgha−1. The variation in regional soil N storage in a typical steppe in Inner Mongolia, China can therefore be simulated using the DNDC model with support from remote sensing.

Population status, habitat associations, and distribution of the steppe polecat Mustela eversmanii in Europe

The steppe polecat Mustela eversmanii is a medium-sized mustelid species whose European population has significantly declined over the past century. However, due to the lack of systematic surveys, little is known about its status and distribution. In this paper, we review the current distribution, habitat associations, and population trends of steppe polecats in Europe and assess the main factors associated with these trends. Our results reveal ongoing population declines in most of the studied countries, which led to fragmentation and local population extinctions at the beginning of the twenty-first century. The species was assessed as rapidly declining in Austria, Czech Republic, Moldova, Slovakia, and Ukraine; declining in Bulgaria; and stable in Hungary. Due to insufficient data, its status was not evaluated for Romania, Poland, and Serbia. M. eversmanii naturally occurs in steppe habitats, but recently seems to have adopted open agricultural landscapes consisting of a mosaic of grasslands, small fields with hedges, and dry embankments. Its distribution often coincides with populations of ground squirrels and hamsters. However, in intensively used agricultural landscapes, smaller rodents (especially voles) could also be an important dietary component. Intensive agricultural production, habitat loss, the degradation of steppe and grassland habitats, and significant declines in the availability of its main prey are the crucial factors for the species’ current population decline. Further research is urgently needed to fill the gaps in our knowledge of its distribution, population densities, feeding ecology, habitat associations, and population genetics. This would enable first steps towards its effective conservation and management strategies.