Grandis Steppe Research Articles

The trade-offs of ecological functions during community restoration in Stipa grandis steppe

The trade-offs of ecological functions during community restoration in Stipa grandis steppe

放牧和刈割对大针茅草原土壤微生物群落结构及多样性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 放牧和刈割对大针茅草原土壤微生物群落结构及多样性的影响 DOI: 10.5846/stxb202103290818 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 内蒙古自治区科技计划项目（2019ZD008）；内蒙古自治区自然科学基金项目（2020ZD03）；国家自然科学基金项目（31861143001，32160332） Effects of management regime on soil microbial community structure and diversity of Stipa grandis grassland Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:放牧和刈割是内蒙古草原的两种主要利用方式，然而，长期放牧和刈割对大针茅草原土壤微生物群落的影响知之甚少，因此，以内蒙古大针茅草原为研究对象，设置放牧和刈割两种利用方式，以围封不利用为对照，基于高通量测序技术，研究大针茅草原在不同利用方式下土壤微生物组成及多样性的变化，并结合土壤理化因子进一步探究土壤微生物群落组成的主要影响因素。研究结果表明：不同利用方式下土壤细菌α多样性指数无显著差异，而刈割显著提高了土壤真菌Observed_species、Chao1和ACE指数；土壤细菌群落的优势菌门是变形菌门（Proteobacteria）和放线菌门（Actinobacteria），土壤真菌群落的优势菌门是子囊菌门（Ascomycota）和被孢霉门（Mortierellomycota），不同利用方式下部分微生物类群的相对丰度差异显著，放牧显著提高了细菌群落的变形菌门、疣微菌门（Verrucomicrobia）和芽单胞菌门（Gemmatimonadetes）的相对丰度，刈割显著提高了真菌群落的担子菌门（Basidiomycota）相对丰度，此外，放牧和刈割均显著降低了厚壁菌门（Firmicutes）的相对丰度；冗余分析表明，土壤细菌主要受硝态氮和铵态氮影响，二者均与酸杆菌门（Acidobacteria）呈正相关，与变形菌门（Proteobacteria）呈负相关，土壤真菌主要受有效磷和硝态氮影响。综上所述，草地利用方式的改变通过土壤理化因子改变了土壤微生群落组成及多样性，其中土壤铵态氮、硝态氮和有效磷是微生物群落形成和演化的主要驱动因素。研究揭示了不同利用方式下大针茅草原土壤微生物群落结构特征及多样性的变化及其与土壤理化性质的关系，可为大针茅草原合理利用提供理论依据。 Abstract:Grazing and mowing are two dominant management regimes in the Inner Mongolia grassland, both of which have a profound impact on grassland ecosystem, and most of the previous studies have primarily focused on the effects on plant and soil. Soil microbial communities are the most abundant and diverse groups of organisms on earth and are responsible for numerous key ecosystem processes. They play an important role in the circulation of materials and nutrients between plants and soil ecosystems. However, their response to these management regimes has not been comprehensively explored in Stipa grandis grassland. In this study, two management regimes of grazing and mowing were set up in a typical S. grandis area, and enclosure was used as the control. Based on high-throughput sequencing technology, the changes of soil microbial composition and diversity under different management regimes was examined, Redundancy analysis was used to analysis soil physical and chemical characteristics influencing on it. The results showed that there was no significant difference in soil bacterial α diversity index under different management regimes, but mowing significantly increased soil fungal Observed_species, Chao1 and ACE index. Amplicon sequencing revealed Proteobacteria and Actinobacteria were the dominant bacterial phylum under different grassland management regimes, and the dominant phyla of soil fungal communities were Ascomycota and Mortierellomycota. Grazing significantly increased the relative abundance of Proteobacteria, Verrucomicrobia and Gemmatimonadetes of the bacterial community, and mowing significantly increased the relative abundance of Basidiomycota of fungal community. In addition, grazing and mowing significantly reduced the relative abundance of Firmicutes. Redundancy analysis showed that soil bacteria were mainly affected by nitrate nitrogen and ammonium nitrogen, which were positively correlated with Acidobacteria and negatively correlated with Proteobacteria. Soil fungi were mainly affected by available phosphorus and nitrate nitrogen. In conclusion, changes in grassland usage methods altered the composition and diversity of soil microflora through soil physicochemical factors, and soil ammonium nitrogen, nitrate nitrogen and available phosphorus were the main driving factors on microbial community formation and evolution. This study revealed the structural characteristics and diversity of soil microbial communities in the S. grandis steppe under different management regimes and their relationship with soil physicochemical properties, which may provide a theoretical basis for the rational utilization of S. grandis steppe. 参考文献 相似文献 引证文献

The composition of antibiotic resistance genes is not affected by grazing but is determined by microorganisms in grassland soils

Grazing is expected to exert a substantial influence on antibiotic resistance genes (ARGs) in grassland ecosystems. However, the precise effects of grazing on the composition of ARGs in grassland soils remain unclear. This is especially the case for grassland soils subject to long-term grazing. Here, we investigated ARGs and bacterial community composition in soils subject to long-term historic grazing (13–39 years) and corresponding ungrazed samples. Using a combination of shotgun metagenomics, amplicon analyses and associated soil physicochemical data, we provide novel insights regarding the structure of ARGs in grassland soils. Interestingly, our analysis revealed that long-term historic grazing had no impacts on the composition of ARGs in grassland soils. An average of 378 ARGs, conferring resistance to 14 major categories of antibiotics (80%), were identified in both grazing and ungrazed sites. Actinobacteria, Proteobacteria and Acidobacteria were the most prevalent predicted hosts in these soils and were also shown to harbour genetic capacity for multiple-resistant ARGs. Our results suggested that positive effects of bacterial community composition on ARGs could potentially be controlled by affecting MGEs. Soil properties had direct effects on the composition of ARGs through affecting the frequency of horizontal gene transfer among bacteria. Twelve novel ARGs were found in S. grandis steppe grasslands, indicating that different vegetation types might induce shifts in soil ARGs. Collectively, these findings suggest that soil properties, plants and microorganisms play critical roles in shaping ARG patterns in grasslands. Together, these data establish a solid baseline for understanding environmental antibiotic resistance in grasslands.

Effects of mowing height on community structure and stability in Stipa grandis steppe

We examined the effects of mowing height on community structure and stability in August from 2014 to 2018 in a Stipa grandis steppe of Xilingol, Inner Mongolia, China. Three mowing height treatments (2, 5 and 8 cm) were manipulated, with enclosure as the control. Results showed that 27 species from 23 genera of 15 families were recorded in the community. The community was dominated by S. grandis, Anemarrhena asphodeloides, Leymus chinensis and Cleistogenes squarrosa. The cumulative relative importance value of those four species was 76.1%. Of all species, there were 15 perennial forbs, 5 annuals biennials, 3 perennial bunch grasses, 3 shrubs semi-shrubs, and 1 perennial rhizome grasses. S. grandis was in the upper layer of the community, L. chinensis and A. asphodeloides were in the middle layer, C. squarrosa, Chenopodium aristatum and Salsola collina were at the bottom layer. Mowing decreased the relative importance value (RIV) of S. grandis and perennial bunch grasses, but increased that of C. squarrosa, C. aristatum, S. collina and annuals biennials. The RIV of L. chinensis was decreased in the 2 cm treatment but increased in the 5 cm and 8 cm treatments. The RIV of A. asphodeloides was increased in the 5 cm treatment but decreased in both the 2 cm and 8 cm treatments. The RIV of perennial forbs was decreased in the 8 cm treatment but increased in both the 2 cm and 5 cm treatments. Species and functional groups diversity showed significant interannual variation. Generally, species richness and diversity were little affected by mowing, while functional groups diversity was significantly impacted, indicating that compensation between different functional groups would stabilize the community under mowing. Mowing increased community stability. Community stability was higher in the 5 cm and 8 cm treatments, with the variability being larger in the 5 cm than in the 8 cm treatment. Therefore, the 8 cm treatment was beneficial for the stability and sustainable utilization of grassland community.

The shift in the abundance of two Stipa species in response to land use change is associated with their divergent reproductive strategies

The divergent changes of plant species under land use changes are key mechanisms underlying vegetation succession. Stipa grandis steppe and Stipa krylovii steppe are two plant communities widely distributed on the Mongolian Plateau. They have been speculated to be able to succeed into each other under different land use types and intensities based on the observations on their presence and abundance at the sites with different land use history. However, no direct evidence, neither the underlying mechanisms, have been reported for this speculation. Here, we verified this speculation and explored the underlying mechanisms in the typical steppe region of Inner Mongolia. We investigated the abundance and reproductive behavior of S. krylovii and S. grandis under different land use types and intensities. We used 18 grassland paddocks to run a 6-year experiment with 6 management treatments (T0—unused, T1—grazing monthly in plant growing season, T2, T4, T6—grazing in different months in plant growing season, and T8—mowing) replicated three times. We measured the relative density and cover of S. krylovii and S. grandis using line sampling method and examined their number and biomass of vegetative and reproductive tillers using quadrat method in each paddock after treatments for 4 and 6 years. We also determined these plant attributes in 14 pairs of heavily versus lightly used grassland plots in a wide area (150 km × 200 km) of the typical steppe region. 1. Grazing largely and mowing moderately decreased the density ratio and coverage ratio of S. grandis to S. krylovii in grasslands (P < 0.05), and the differences in these ratios between grazed and unused grasslands increased with time. 2. Grazing, but not mowing, significantly enhanced the relative density (Nᵣₑₚ = reproductive tiller number/total tiller number) of, and biomass allocation (Bᵣₑₚ = reproductive tiller biomass/total biomass) to, reproductive tillers of S. krylovii (P < 0.05), but not S. grandis. This grazing enhancement to sexual reproduction of S. krylovii, and additionally inhibition to Nᵣₑₚ of S. grandis (P < 0.05), were found across the 14 pairs of heavily versus lightly used plots. 3. Seasonal pattern of grazing affected sexual reproduction of S. krylovii. The Nᵣₑₚ and Bᵣₑₚ was higher under grazing in July and September (T4) than in July and August (T6) or in May and July (T2) (P < 0.05), suggesting a relatively positive effect of grazing on sexual reproduction in July (tasseling phenophase) than in May or August. Our results provide direct evidence to the reciprocal change of S. grandis and S. krylovii in steppe communities under different management and indicate that gazing or mowing enhancement of sexual reproduction of S. krylovii relative to S. grandis is one of the mechanisms for the change.

放牧对大针茅草原建群种与优势种空间分布关系的影响

放牧对大针茅草原建群种与优势种空间分布关系的影响

Soil bacterial community shifts driven by restoration time and steppe types in the degraded steppe of Inner Mongolia

Degraded grassland can be restored through management practices such as fencing to protect land from overgrazing. However, little is known about the dynamics of underground microbial communities and their associated ecological function during the restoration process. In this study, we investigated changes in the soil bacterial community composition with varying restoration time in the Leymus chinensis steppe. We also studied the differences in the soil bacterial community composition between a Leymus chinensis steppe and a Stipa grandis steppe at the same restoration time in the Inner Mongolia of China. Results showed that restoration of the degraded steppe through fencing significantly changed the bacterial community composition through the restoration time. The relative abundances of Chloroflexi and Cyanobacteria decreased significantly with restoration. However, the relative abundances of copiotrophic Proteobacteria and Bacteriodetes increased. Significant changes for many dominant taxa occurred between 7 and 13 years of restoration time in the Leymus chinensis steppe. Shifts in the composition of bacterial communities with fencing and grazing were driven by multiple factors, including soil moisture, pH, nutrients (organic carbon and nitrogen, etc.). Network analysis of soil bacterial community compositions showed that the three largest modules in co-occurrence networks were separated by fencing, grazing and steppe type. This study revealed the successions of underground microbial communities associated with steppe restoration management over time.

Influence of Different Mowing Systems on Community Characteristics and the Compensatory Growth of Important Species of the Stipa grandis Steppe in Inner Mongolia

The Stipa grandis steppe is a type of steppe in the Central Asian sub-region, and it is an important resource for livestock production in China. Mowing is one of the main management methods for this steppe. Verifying the response of the Stipa grandis steppe communities to different mowing frequencies is essential for the rational utilization of pastures and the protection and recovery of natural steppe. In this study, we investigated the community characteristics and compensatory growth of important species of the Stipa grandis steppe community under four mowing frequencies (TAY: twice a year; OAY: once a year; OTY: once every other year; NM: no mowing/enclosure), and found that different frequencies of mowing significantly influenced the community characteristics and the compensatory growth of dominant plant species. In the enclosure, species density was significantly lower, and height and biomass were significantly greater than in the mowing treatments. At the beginning of the growing season, mowing had a significant impact on the individual miniaturization of Stipa grandis, Leymus chinensis, and Anemarrhena asphodeloides. Mowing also had a significant impact on the diversity of the community. The Shannon diversity index, the Pielou evenness index, and the richness index were higher under OTY than other mowing frequencies. Under different mowing frequencies, growth rates were significantly different after the aboveground portions were cut, while the levels of biomass were not significantly different. Stipa grandis, Leymus chinensis, and Anemarrhena asphodeloides had less compensatory height growth under OAY compared to the other treatments; however, there were no significant differences in the relative growth rates of the three species under different treatments. Stipa grandis exhibited equivalent compensatory height growth; both Leymus chinensis and Anemarrhena asphodeloides exhibited over-compensatory growth. Based on the results of community characteristics and the compensatory growth of the dominant species, mowing every other year is currently the most practical mowing system.

不同刈割频度对大针茅草原群落特征及土壤元素含量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同刈割频度对大针茅草原群落特征及土壤元素含量的影响 DOI: 10.5846/stxb201507121473 作者: 作者单位: 内蒙古大学生命科学学院，中国农业科学院农业环境与可持续发展研究所,内蒙古大学生命科学学院,中国农业科学院农业环境与可持续发展研究所,内蒙古大学，中国农业科学院农业环境与可持续发展研究所,内蒙古大学，中国农业科学院农业环境与可持续发展研究所,内蒙古大学,中国农业科学院农业环境与可持续发展研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 内蒙古自然科学基金项目（2014ZD02）；农业部资助项目（国家牧草现代产业技术体系，CARS-35）；国家科技支撑计划专题项目（2013BAC09B03-2） Effects of different mowing frequency on the community characteristics and soil element contents in a Stipa grandis steppe ecosystem Author: Affiliation: School of Life Sciences, Inner Mongolia University,School of Life Sciences, Inner Mongolia 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:在草原生态系统中，土壤是植物生长发育最重要的基质，对植物群落动态有显著的影响。刈割是内蒙古典型草原区除放牧外最重要的利用方式。研究不同刈割频度对典型草原区群落特征和若干土壤性质的影响及土壤因子与群落特征的相关性，旨在得出对群落多样性最有利并最适宜生产利用的刈割频度。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原；在2009-2013年进行不同频度的刈割处理，共设置处理，一年两次刈割、一年一次刈割、两年一次（割一年休一年）刈割、围封，在2013年8月采集测定土壤养分的样品。刈割对群落多样性影响显著，割一年休一年Shannon-Wiener多样性指数、Pielou均匀度指数、丰富度指数均高于其他刈割处理（P<0.05）；不同频度刈割下，一年两次刈割处理下土壤20-30cm和30-40cm的有机质含量显著高于其他处理（P<0.05）；不同频度刈割处理下土壤中的速效磷和速效氮的含量没有显著差异；一年两次处理的土壤全氮含量显著高于其他处理（P<0.05）。Shannon-Wiener多样性指数与有机质含量、全氮含量呈显著负相关；Pielou均匀度指数与土壤元素间无显著相关关系；Richness指数与有机质含量呈显著负相关，与全氮含量为极显著负相关关系。割一年休一年刈割处理下土壤元素含量呈现更好的状态，结合群落物种多样性及生产利用的角度，割一年休一年为最合理的刈割频度。 Abstract:In grassland ecosystems, soil is the most important substrate for plant growth and has a significant impact on Plant community dynamics. Mowing is the most important way to use steppes in Inner Mongolia, except for grazing. In the present study, the impact of different mowing frequencies on the community characteristics and soil properties, and the correlation between soil factors and community characteristics were studied. The aim was to determine the most efficient and suitable mowing system for enhanced productivity and community diversity. The study area is a typical steppe primarily based on Stipa grandis, located in the Maodeng pasture of eastern Xilinhaote City, Inner Mongolia, the mowing frequency were set four gradient(TAY:Twice a year;OAY:Once a year; OTY:Once two year; NM:No mowing). Different mowing treatments were conducted in 2009-2013, soil samples were collected and analyzed in August 2013. The results indicated that the mowing treatments significantly affected plant community diversity(P<0.05). The Shannon-Wiener diversity index, Pielou evenness index, and species richness index for the mowing once-in-two-years treatment were higher than those for the other treatments. The organic matter contents of 20-30 cm and 30-40 cm soil in the mowing twice-in-one-year treatment were significantly higher than those in other treatments(P<0.05). There were no significant differences in the available nitrogen and phosphorus contents of soil between the different treatments. In addition, the soil total nitrogen in the mowing twice-in-one-year treatment was significantly higher than that in other treatments(P<0.05). The correlation analysis showed the Shannon-Wiener diversity and species richness indices were significantly negatively correlated with organic matter and total nitrogen contents, where as the Pielou evenness index had no correlation with soil element content, Richness index was significantly negatively correlated with total nitrogen content and organic matter content. Fencing was significantly beneficial to soil nutrients, but not conducive to the growth of dominant species, plant community species diversity, and increasing the plant community density. Combining the results for species diversity and production, an annual mowing interval was the most efficient mowing method for the steppe ecosystem. 参考文献 相似文献 引证文献

Simulated water fluxes during the growing season in semiarid grassland ecosystems under severe drought conditions

summary To help improve understanding of how changes in climate and land cover affect water fluxes, water budgets, and the structure and function of regional grassland ecosystems, the Grassland Landscape Productivity Model (GLPM) was used to simulate spatiotemporal variation in primary water fluxes. The study area was a semiarid region in Inner Mongolia, China, in 2002, when severe drought was experienced. For Stipa grandis steppe, Leymus chinensis steppe, shrubland, and croplands, the modeled total, daily and monthly averaged, and maximum evapotranspiration during the growing season and the modeled water deficits were similar to those measured in Inner Mongolia under similar precipitation conditions. The modeled temporal variations in daily evaporation rate, transpiration rate, and evapotranspiration rate for the typical steppes also agreed reasonably well with measured trends. The results demonstrate that water fluxes varied in response to spatiotemporal variations in environmental factors and associated changes in the phenological and physiological characteristics of plants. It was also found that transpiration and evapotranspiration (rather than precipitation) were the primary factors controlling differences in water deficit among land cover types. The results also demonstrate that specific phenomena occur under severe drought conditions; these phenomena are considerably different to those occurring under normal or well-watered conditions. The findings of the present study will be useful for evaluating day-scale water fluxes and their relationships with climate change, hydrology, land cover, and vegetation dynamics. 2014 Published by Elsevier B.V.

Effects of Rest Grazing on Organic Carbon Storage in Stipa grandis Steppe in Inner Mongolia, China

This study was aimed to evaluate the potential effects of rest grazing on organic carbon storage in Stipa grandis steppe of Inner Mongolia, China. Using potassium dichromate heating method, we analyzed the organic carbon storage of plant and soil in Stipa grandis steppe after rest grazing for 3, 6, and 9 yr. The results indicated that as the rest grazing ages prolonged, the biomass of aboveground parts, litter and belowground plant parts (roots) of the plant communities all increased, meanwhile the C content of the biomass increased with the rest grazing ages prolonging. For RG0, RG3a, RG6a, and RG9a, C storage in aboveground vegetation were 60.7, 76.9, 82.8 and 122.2 g C m−2, respectively; C storage of litter were 5.1, 5.8, 20.4 and 25.5 g C m−2, respectively; C storage of belowground roots (0–100 cm) were 475.2, 663.0, 1 115.0 and 1 867.3 g C m−2, respectively; C storage in 0–100 cm soil were 13.97, 15.76, 18.60 and 32.41 kg C m−2, respectively. As the rest grazing ages prolonged, the organic C storage in plant communities and soil increased. The C storage of belowground roots and soil organic C was mainly concentrated in 0–40 cm soil body. The increased soil organic C for RG3a accounted for 89.8% of the increased carbon in vegetation-soil system, 87.2% for RG6a, and 92.6% for RG9a. From the perspective of C sequestration cost, total cost for RG3a, RG6a, and RG9a were 2 903.4, 5 806.8 and 8 710.2 CNY ha−1, respectively. The cost reduced with the extension of rest grazing ages, 0.15 CNY kg−1 C for RG3a, 0.11 CNY kg−1 C for RG6a and 0.04 CNY kg−1 C for RG9a. From the growth characteristics of grassland plants, the spring was one of the two avoided grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. Organic C storage for RG9a was the highest, while the cost of C sequestration was the lowest. Therefore, spring rest grazing should be encouraged because it was proved to be a very efficient grassland use pattern.

Traits related to carbon sequestration of common plant species in a Stipa grandis steppe in Nei Mongol under different land-uses

Traits related to carbon sequestration of common plant species in a Stipa grandis steppe in Nei Mongol under different land-uses

Point pattern analysis of dominant populations in a degraded community in &lt;I&gt;Leymus chinensis&lt;/I&gt; + &lt;I&gt;Stipa grandis&lt;/I&gt; steppe in Inner Mongolia, China

Point pattern analysis of dominant populations in a degraded community in &lt;I&gt;Leymus chinensis&lt;/I&gt; + &lt;I&gt;Stipa grandis&lt;/I&gt; steppe in Inner Mongolia, China

Annual methane uptake by temperate semiarid steppes as regulated by stocking rates, aboveground plant biomass and topsoil air permeability

AbstractOvergrazing‐induced degradation of temperate semiarid steppes may affect the soil sink for atmospheric methane (CH4). However, previous studies have primarily focused on the growing season and on single grazing patterns. Thus, the response of annual CH4 uptake by steppes compared with various grazing practices is uncertain. In this study, we investigated the effects of grazing on the annual CH4 uptake by two typical Eurasian semiarid steppes (the Stipa grandis steppe and the Leymus chinensis steppe) located in Inner Mongolia, China. The CH4 fluxes were measured year‐round using static chambers and gas chromatography at 12 field sites that differed primarily in grazing intensities. Our results indicated that steppe soils were CH4 sinks throughout the year. The annual CH4 uptake correlated with stocking rates, whereas the seasonality of CH4 uptake was primarily dominated by temperature. The annual CH4 uptake at all sites averaged 3.7±0.7 kg C ha−1 yr−1 (range: 2.3–4.5), where approximately 35% (range: 23–40%) occurred during the nongrowing season. Light‐to‐moderate grazing (stocking rate≤1 sheep ha−1 yr−1) did not significantly change the annual CH4 uptake compared with ungrazed steppes, but heavy grazing reduced annual CH4 uptake significantly (by 24–31%, P&lt;0.05). These findings imply that easing the pressure of heavily grazed steppes (e.g. moving to light or moderate stocking rates) would help restore steppe soil sinks for atmospheric CH4. The empirical equations based on the significant relationships between annual CH4 uptake and stocking rates, aboveground plant biomass and topsoil air permeability (P&lt;0.01) could provide simple approaches for the estimation of regional CH4 uptake by temperate semiarid steppes.

Grazing Effects on Compressibility of Kastanozems in Inner Mongolian Steppe Ecosystem

In Inner Mongolia, animal trampling is one of the main factors causing soil degradation manifested by altered mechanical strength or changes in water and gas fluxes. Soil samples were collected at two depths (4–8 and 18–22 cm) on the Stipa grandis steppe ecosystem in Inner Mongolia from two treatments characterized by different grazing intensities: ungrazed since 1979 (UG) and continuously grazed (CG). The following mechanical soil properties were determined under static and repeated loading conditions: precompression stress, Pc; coefficient of cyclic compressibility, cn, and compression index, Cc Air conductivity measurements were used to quantify the changes in soil functions due to application of repeated loading. The CG site showed significantly higher precompression stress values (111 kPa) than the UG site (64 kPa) at the first soil depth. The highest cn values were found in the topsoil of the UG site, while the CG site had significantly lower cn values. Repeated loading caused higher soil deformation compared to the static loading test. It was also found that the strain of soil samples from the UG site was higher than the CG site. We found a good fit between cn and precompression stress. The Cc values of the cyclically loaded samples were significantly lower at the CG site than the statically loaded ones. The air conductivity of the UG site remained constant for a wider stress range of repeatedly applied stress compared with the CG site, which reflects higher stability of the soil pore network at the UG site.

Spatial-temporal variation in soil respiration and its controlling factors in three steppes of Stipa L. in Inner Mongolia, China

Grassland is the largest terrestrial ecosystem in China. It is of great significance to measure accurately the soil respiration of different grassland types for the contribution evaluation of the Chinese terrestrial ecosystem’s carbon emission to the atmospheric CO2 concentration. A three-year (2005–2007) field experiment was carried out on three steppes of Stipa L. in the Xilin River Basin, Inner Mongolia, China, using a static opaque chamber technique. The seasonal and interannual variations of soil respiration rates were analyzed, and the annual total soil respiration of the three steppes was estimated. The numerical models between soil respiration and water-heat factors were established respectively. Similar seasonal dynamic and high annual and interannual variations of soil respiration were found in all of the three steppes. In the growing season, the fluctuation of soil respiration was particularly evident. The coefficients of variation (CVs) for soil respiration in different growing seasons ranged from 54% to 93%, and the annual CVs were all above 115%. The interannual CV of soil respiration progressively decreased in the order of Stipa grandis (S. grandis) steppe > Stipa baicalensis (S. baicalensis) steppe > Stipa krylovii (S. krylovii) steppe. The annual total soil respiration for the S. baicalensis steppe was 223.62–299.24 gC m−2 a−1, 150.62–226.99 gC m−2 a−1 for the S. grandis steppe, and 111.31–131.55 gC m−2 a−1 for the S. krylovii steppe, which were consistent with the precipitation gradient. The variation in the best fitting temperature factor explained the 63.5%, 73.0%, and 73.2% change in soil respiration in the three steppes at an annual time scale, and the corresponding Q10 values were 2.16, 2.98, and 2.40, respectively. Moreover, the Q10 values that were calculated by soil temperature at different depths all expressed a 10 cm > 5 cm > surface in the three sampling sites. In the growing season, the soil respiration rates were related mostly to the surface soil moisture, and the 95.2%, 97.4%, and 93.2% variations in soil respiration in the three steppes were explained by the change in soil moisture at a depth of 0–10 cm, respectively.

Vegetation of the Stipa loess steppe in Ningxia (northern China) in relation to grazing intensity

AbstractLarge areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650–1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species (A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity (r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity.

Examining the genetic diversity of Stipa grandis under various grazing pressures

The Stipa grandis steppe in the Inner Mongolia Autonomous Region occupies an area of 2798081 hm 2. On the basis of the genetic variation, it was found that its adaptability to the environmental conditions under grazing pressure was significant. Using the Inter-Simple Sequence Repeat (ISSR) procedure, the changes to the genetic diversity of the Stipa grandis population under different grazing pressures were observed. Plant samples were collected from a series of grazing gradients of the Stipa grandis steppe in Dalinuoer National Nature Reserve in the Inner Mongolia (located at 116°38′–116°41′E and 43°25′–43°27′N.), which has the following vegetation types in abundance: Leymus chinensis is the constructive species; the dominant species include Stipa grandis, Cleistogenes squarrosa, and Artemisia frigida; the companion species is Potentilla acaulis and others. According to the grazing pressure, the following four grazing gradients were identified from the dwellings of the herdsmen to the enclosure site: (1) no grazing (CK enclosure site); (2) light grazing (LG); (3) moderate grazing (MG); (4) heavy grazing (HG). Young leaves of each Stipa grandis were collected during the growing season. The results showed that the Stipa grandis showed abundant genetic diversity despite the fact that certain polymorphic loci were lost; at the same time, new polymorphic loci emerged when grazing pressure increased; a total of 10 primers were used, and 74 bands were produced in total, of which 65 bands were polymorphic; the total percentage of polymorphism was 89%; the percentage of polymorphic loci of the Stipa grandis population decreased with the increase of grazing pressure; the percentage of polymorphic loci was 62.2% in the no-grazing (CK) population, 64.9% in the light-grazing (LG) population, 58.1% in the moderate-grazing (MG) population, and 56.8% in the heavy-grazing (HG) population; the genetic diversity of the population in the descending order using the Shannon's information index is as follows: (1) light grazing (0.3486); (2) no grazing (0.3339); (3) moderate grazing (0.3249); (4) heavy grazing (0.2735) with the same distributional pattern as the Nei's genetic diversity index. The test showed the following: As the grazing pressures increased, the change of genetic diversity decreased; the genetic differentiation coefficient among the population ( Gst) was 0.1984, which showed the presence of small partial genetic diversity (19.8%) among populations; gene flow ( Nm *) between primers varied from 0.9806 to 3.4463, and the mean gene flow ( Nm *) was 2.0202; the UPGMA cluster figure that was constructed on the basis of the genetic distance matrix showed four populations that became genetically closer at each step: (1) The first group was the moderate-grazing (MG) population and the heavy- grazing (HG) population; (2) The second group consisted of the no-grazing (CK) population and the light-grazing (LG) population; (3) The two groups gathered together.

Interannual variation in the climate and above-ground biomass of Leymus chinense steppe and Stipa grandis steppe in the Xilin river basin, Inner Mongolia, China

We evaluated the relationship between variability in climate and variability in primary production and efficiencies of water use of Leymus chinense steppe and Stipa grandis steppe during 1980–89. On average, annual precipitation was 313·3 mm, while peak above-ground live biomass (PALB) and peak standing crop (PSC) were 182·68 g.m −2 and 193·48 g.m −2 for L. chinense steppe, 144·43 g.m −2 and 152·12 g.m −2 for S. grandis steppe. The coefficient of variation (CV) in annual precipitation was 22%, while the CV in PALB and PSC were 29% and 26% for L. chinense steppe, 24% and 25% for S. grandis steppe. Rain-use efficiency was 6·3 kgDM.ha −1 mm −1 year −1 for L. chinense steppe and 4·9 for S. grandis steppe, using PSC as the estimate of ANPP. Monthly and seasonal patterns of precipitation were as important as annual precipitation in determining responses of these two steppes.

Sensitivity of Inner Mongolia Grasslands to Climate Change

We investigated the effects of global climate change and doubled atmospheric CO2 concentration to plant primary production and soil organic matter of typical steppe (Leymus chinense steppe and Stipa grandis steppe) and meadow steppe (Filifolium sibiricum steppe, S. baicalensis steppe and L. chinense steppe) at individual sites in Inner Mongolia, using the CENTURY ecosystem model. In the simulation of climate change, loss of soil organic C ranges from 783 gC.m-2 in meadow steppe to 1485 gC.m-2 in typical steppe, and annual above-ground net primary production (ANPP) decreases by 17.6 gC.m-2 in meadow steppe to 29.5 gC.m-2 in typical steppe under CCC (Canadian Climate Center). While under GFDL (Geophysical Fluid Dynamics Laboratory), loss of soil organic C varies from 584 gC.m-2 in typical steppe to 1164 gC.m-2 in meadow steppe, and ANPP decreases in the range of 18.3 gC.m-2 in typical steppe to 32.1 gC.m-2 in meadow steppe. In the simulations of climate change plus elevated CO2 (from 350 p.p.m. to 700 p.p.m.), ANPP decreases by 5.4 gC.m-2 in meadow steppe to 11.3 gC.m-2 in typical steppe under CCC +CO2, while ANPP varies from an increase of 1.8 gC.m-2 in S. grandis steppe to a decrease of 20.6 gC.m-2 in meadow steppe under GFDL + CO2. Losses of soil organic C are slightly lower (in the range of 42 gC.m 2 to 248 gC.m -2) than losses of soil organic C under climate