Alpine Meadow Steppe Research Articles

Photo-protective mechanisms in reed canary grass to alleviate photo-inhibition of PSII on the Qinghai-Tibet Plateau

Due to its characteristic of high biomass yield potential, there is considerable interest in cultivating Phalaris arundinacea L. cv. ‘chuancaoyin No.3' (reed canary grass) on the Qinghai-Tibet Plateau where there is an abundance of alpine steppe meadow and a potential large market for animal husbandry. In this study, we 1) investigate whether reed canary grass exhibits superior productive capacity to Elymus nutans ‘Aba' (E. nutans), ordinary common pasture, during the long warm days of summer at high-altitude; and 2) compare the cold tolerance between reed canary grass and E. nutans, including photosynthesis, photo-inhibition, and photo-protection. The results suggest that reed canary grass exhibits higher photosynthetic capacity compared to E. nutans at latitudes of the cool temperate zone. Meanwhile, cold-induced photo-inhibition and photo-damage at high altitudes in reed canary grass were due to both stomatal and non-stomatal limitation, and the enhancement in photo-respiration, thermal dissipation, and Mehler reaction are important processes to minimize the negative effects of high elevation and a cold environment.

Relationships between plateau pika (Ochotona curzoniae) densities and biomass and biodiversity indices of alpine meadow steppe on the Qinghai–Tibet Plateau China

Variations of plant biomass and plant species diversity in relation to plateau pika densities in alpine meadow steppe of the Qinghai-Tibet Plateau China were investigated. Peak above- and below-ground biomass, botanical composition, and soil moisture were measured and from these species and functional diversity indices were calculated with reference to pika burrow densities, biomass and soil moisture. Biomass components generally decreased with increased pika burrow density. Biomass of sedges and forbs increased whereas aboveground biomass of grasses first increased and then decreased as burrow density increased. There were positive linear relationships between aboveground biomass and both species and functional group richness and diversity, and also between soil moisture and these indices. These results are relevant to considerations of whether plateau pika is a pest or is a key species in maintaining the ecological stability and biodiversity of its indigenous habitat.

The role of permafrost and soil water in distribution of alpine grassland and its NDVI dynamics on the Qinghai-Tibetan Plateau

Soil temperature and soil water are two important factors controlling vegetation growth. Climate warming and associated permafrost degradation might change these soil conditions and affect alpine grassland on the Qinghai-Tibetan Plateau. However, our current understanding of the role of soil temperature and water at the plateau scale is inadequate. In this study, we used plateau scale soil water content, frozen soil type, vegetation index and land surface temperature datasets to investigate the spatial distribution, limiting factors of vegetation growth and normalized difference vegetation index (NDVI) changing trends in two major alpine grasslands, alpine meadow and alpine steppe, in relation to soil temperature and soil water conditions. Our results showed that: 1) alpine meadow is mainly distributed in seasonal frozen soil areas (55.90% of alpine meadow) with a soil water content between 0.15 and 0.25m3/m3 and alpine steppe is mainly found in seasonal frozen and sub-stable permafrost areas (69.38% of alpine steppe) with a soil water content between 0.05 and 0.20m3/m3; 2) at the plateau scale, there were 35.6% (more in colder regions) of alpine meadow pixels and 33.6% (more in wetter regions) of alpine steppe pixels having increase NDVI changing trends during 1982–2012, respectively; and the values having decrease NDVI changing trends are 7.3% and 9.7%, respectively; and 3) the vegetation growth of alpine meadow is mainly limited by soil temperature, while that of alpine steppe is limited by both soil temperature and soil water. We also find the limiting factors of temperature or water can only explain <50% variation of vegetation growth trends in alpine grasslands. Our findings warrant the use of process-based ecosystem models to consider other factors, such as grazing, erosion and soil texture, among others, in addition to soil temperature and water to make proper projections when simulating the responses of vegetation growth to climate warming in alpine grasslands with different hydro-thermal conditions.

Effects of grazing exclusion on carbon sequestration and plant diversity in grasslands of China—A meta-analysis

Widespread land degradation has strengthened the urgent need to restore overgrazing grasslands. China has implemented the program ‘Returning Grazing Land to Grassland’ (RGLG) through grazing exclusion by fence since 2003. Despite a lot of field experiments, there is still controversy on the effects of grazing exclusion on rangeland restoration, highlighting the need for synthetic analysis. We conducted a meta-analysis of 447 entries from 78 papers to analyze the spatiotemporal effects of grazing exclusion on plant diversity, productivity and soil carbon sequestration in the major RGLG-implemented provinces of China. Our results showed that, compared with the grazed sites, grazing exclusion significantly increased carbon stored in aboveground biomass, litter mass, belowground biomass and soils by 84.7%, 111.6%, 25.5% and 14.4%, respectively. Plant coverage, soil available nitrogen, soil available phosphorus and soil microbial biomass carbon increased by 52.0%, 21.7% 22.8% and 26.3%, respectively. However, grazing exclusion had little effects on recovering plant diversity in China’s grasslands. Of the factors examined, climatic factors strongly modified the effects of grazing exclusion on ecosystem carbon stocks, for example, precipitation significantly amplified the positive effects. Grazing exclusion played a positive role in soil carbon sequestration in most grassland types except in temperate desert-steppe. But annual soil carbon sequestration rates decayed rapidly over time in both alpine meadow and temperate steppe. Short-term (≤5years) grazing exclusion remarkably increased species richness, but not significantly in the long run. The threshold from neutral to negative effects of grazing exclusion on species evenness occurs after approximately ten years. Our findings provide evidence that grazing exclusion is an effective way to restore vegetation and sequestrate carbon in degraded grasslands, but not beneficial to plant diversity maintenance. The benefits of grazing exclusion are more effective in humid area than arid area. We suggest that grazing exclusion should be ceased after about six to ten years. Additionally, grazing exclusion should integrate with other appropriate management practices instead of operating on a stand-alone basis.

西藏高原草地生态系统丛枝菌根真菌的地理分布

PDF HTML阅读 XML下载 导出引用 引用提醒 西藏高原草地生态系统丛枝菌根真菌的地理分布 DOI: 10.5846/stxb201411192291 作者: 作者单位: 西藏大学农牧学院,西藏大学农牧学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41161043,41461054) Geographical distribution of arbuscular mycorrhizal fungi in the grassland ecosystems of the Tibetan Plateau Author: Affiliation: Agricultural and Animal Husbandry College,Tibet University,Agricultural and Animal Husbandry College,Tibet 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:西藏高原是地球上极具特色的地理单元,对生物物种的形成与演化具有重要影响。基于孢子形态学鉴定,对从藏东南到藏西北(海拔高差 > 3500 m,年均温、年均降水量差异分别 > 20 ℃、 > 800 mm)高原热带、亚热带、温带、亚寒带和寒带环境下发育而成的热性草丛、暖性草丛、温性草原、温性荒漠、高寒草甸草原、高寒草原、高寒荒漠和高寒荒漠草原中的AM真菌群落进行研究,结果表明,不同类型草地间AM真菌的群落相似度普遍较低,环境对AM真菌群落具有重要影响。从藏东南到藏西北,不同类型草地间AM真菌的群落相似度呈下降趋势(Jaccard相似性系数从0.52降至0.20),AM真菌群落组成及结构变化渐趋加大,不同草地中的同种植物(包括广谱种、青藏高原特有种)AM真菌群落相似度亦不同。沿藏东南到藏西北环境梯度,随草地寒旱程度的逐步加剧,AM真菌种的丰度,特别是种数、Shannon-Weiner指数在总体上趋于显著(P < 0.05)下降,孢子密度则在总体上趋于显著提高,优势种比例、Shannon-Weiner指数亦表现出增加的趋势,表明AM真菌物种多样性虽趋于下降,但生存及对环境的适应能力趋于提高。海拔、土壤pH、有效磷和有机碳含量对AM真菌群落组成均具显著影响,但海拔对水热环境的影响决定着土壤环境的变化。因此,海拔和寒旱程度不断上升所导致的pH显著提高、土壤有机碳和有效磷含量显著下降的综合作用影响并决定着AM真菌的群落组成。研究结果对进一步理解西藏高原生物多样性的产生和维持机制等具有重要的参考价值。 Abstract:The Tibetan plateau is a unique geographical unit that plays important roles in the formation and evolution of biological species. On the basis of spore morphology, we preliminarily investigated arbuscular mycorrhizal (AM) fungal communities in tropical tussock (TT), warm tussock (WT), temperate desert steppe (TDS), temperate desert (TD), alpine meadow steppe (AMS), alpine steppe (AS), alpine desert (AD), and alpine desert steppe (ADS) environments in southeastern to northwestern Tibet (altitude > 3500 m; mean annual temperature difference > 20 ℃; mean annual amount of precipitation difference > 800 mm), including plateau tropic, subtropic, temperate, subfrigid, and frigid zones. The results showed that the community similarity of AM fungi in different types of grasslands was generally low, and the type of environment had an important effect on the AM fungal community. Community similarity of AM fungi in different types of grassland demonstrated a decreasing trend from southeastern to northwestern Tibet (Jaccard similarity coefficient decreased from 0.52 to 0.20). Changes in the composition and structure of the AM fungal community increased gradually. AM fungal community similarity for the same plant species (including a broad spectrum of species and species endemic to the Qinghai-Tibetan Plateau) in different grasslands was also different. With a gradually aggravated degree of cold and drought in the grasslands along the environmental gradient from southeastern to northwestern Tibet, the abundance of AM fungi species, especially the number of species, showed significantly decreasing trends, according to the Shannon-Weiner index (P < 0.05). At the same time, spore density demonstrated dramatically increasing trends, and the proportion of dominant species in relation to the Shannon-Weiner index also showed a tendency to increase. This indicated that although the diversity of AM fungi showed decreasing trends, their survival and adaptability to the environment tended to improve. The effects of altitude, soil pH, effective phosphorus, and organic carbon content on AM fungal communities were significant, whereas the effects of altitude on the hydrothermal environment determined the changes in the soil environment. Therefore, AM fungal community composition was determined by the comprehensive effects of a dramatic increase in pH and soil organic carbon and a dramatic decrease in effective phosphorus content due to the gradually increasing altitude and degree of cold and drought. Our results have an important reference value for the further understanding of the production and maintenance of organism diversity in the Tibetan Plateau. 参考文献 相似文献 引证文献

Soil nitrogen and carbon determine the trade-off of the above- and below-ground biomass across alpine grasslands, Tibetan Plateau

The objective of this study is to gain a deeper understanding of the trade-offs between the aboveground biomass (AGB) and belowground biomass (BGB) due to environmental factors in alpine grasslands, including alpine steppes and alpine meadows, on the Tibetan Plateau. We assessed transect surveys to determine the response threshold and critical determinant of trade-offs. Additionally, a non-significant relationship was observed between trade-offs and climate factors and soil properties when the data for the alpine meadow and alpine steppe were analyzed separately. However, the trade-off between AGB and BGB were increased with soil nitrogen and organic carbon gradients across the alpine grassland. The results demonstrate the trade-off effects of AGB and BGB in alpine grasslands, emphasizing the need for an understanding of how the trade-off is affected by drivers of critical environmental factors at the regional scale. Consequently, trade-offs are an ecological indicator and tool for ecological management and decision-making.

A remote sensing model to estimate ecosystem respiration in Northern China and the Tibetan Plateau

Ecosystem respiration (Re) is rarely quantified from remote sensing data because satellite technique is incapable of observing the key processes associated with soil respiration. In this study, we develop a Remote Sensing Model for Re (ReRSM) by assuming that one part of Re is derived from current photosynthate with the respiratory rate coupling closely with gross primary production (GPP), and the other part of Re is derived from reserved ecosystem organic matter (including plant biomass, plant residues and soil organic matter) with the respiratory rate responding strongly to temperature change. The ReRSM is solely driven by the Enhanced Vegetation Index (EVI), the Land Surface Water Index (LSWI) and the Land Surface Temperature (LST) from MODIS data. Multi-year eddy CO2 flux data of five vegetation types in Northern China and the Tibetan Plateau (including temperate mixed forest, temperate steppe, alpine shrubland, alpine marsh and alpine meadow-steppe) were used for model parameterization and validation. In most cases, the simulated Re agreed well with the observed Re in terms of seasonal and interannual variation irrespective of vegetation types. The ReRSM could explain approximately 93% of the variation in the observed Re across five vegetation types, with the root mean square error (RMSE) of 0.04molCm−2d−1 and the modeling efficiency (EF) of 0.93. Model comparison showed that the performance of the ReRSM was comparable with that of the RECO in the studied five vegetation types, while the former had much fewer parameters than the latter. The ReRSM parameters showed good linear relationships with the mean annual satellite indices. With these linear functions, the ReRSM could explain approximately 90% of the variation in the observed Re across five vegetation types, with the RMSE of 0.05molCm−2d−1 and the EF of 0.89. These analyses indicated that the ReRSM is a simple and alternative approach in Re estimation and has the potential of estimating spatial Re. However, the performance of ReRSM in other vegetation types or regions still needs a further study.

Changes in vegetation composition and plant diversity with rangeland degradation in the alpine region of Qinghai-Tibet Plateau

The changes in vegetation composition and plant diversity of three different alpine ecosystems: alpine meadow, alpine steppe and alpine desert, impacted by different levels of degradation (healthy, lightly degraded and moderately degraded) were examined across a large-scale transect on the Qinghai-Tibet Plateau. The alpine meadow was dominated by sedges, the alpine steppe was dominated by grasses and the alpine desert was dominated by shrubs. The alpine meadow had the highest species diversity, whereas the alpine steppe had the lowest and tended to be dominated by a few species. Forbs were the dominant and most diverse functional group in the alpine meadow and the alpine steppe, which was different from the alpine desert. The importance values of the dominant species and levels of diversity measured by various vegetation indices were only slightly different in the degraded sites as compared with the non-degraded alpine meadow and steppe, whereas the alpine desert showed large changes in the composition and diversity of the plant community in response to degradation. In conclusion, the plant composition of the alpine meadow and alpine steppe ecosystems was more stable and appeared more resistant to disturbance than that of the alpine desert ecosystem.

Lagged climatic effects on carbon fluxes over three grassland ecosystems in China

Aims The plasticity of ecosystem responses could buffer and postpone the effects of climates on ecosystem carbon fluxes, but this lagged effect is often ignored. In this study, we used carbon flux data collected from three typical grassland ecosystems in China, including a temperate semiarid steppe in Inner Mongolia (Neimeng site, NM), an alpine shrub-meadow in Qinghai (Haibei site, HB) and an alpine meadow steppe in Tibet (Dangxiong site, DX), to examine the time lagged effects of environmental factors on CO2 exchange. Methods Eddy covariance data were collected from three typical Chinese grasslands. In linking carbon fluxes with climatic factors, we used their averages or cumulative values within each 12-month period and we called them 'yearly' statistics in this study. To investigate the lagged effects of the climatic factors on the carbon fluxes, the climatic 'yearly' statistics were kept still and the 'yearly' statistics of the carbon fluxes were shifted backward 1 month at a time. Important Findings Soil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine HB and DX, respectively, while the NM site was under a synthetic impact of each climatic factor. The time lagged effect analysis showed that temperature had several months, even half a year lag effects on CO2 exchange at the three studied sites, while moisture's effects were mostly exhibited as an immediate manner, except at NM. In general, the lagged climatic effects were relatively weak for the alpine ecosystem. Our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate, so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability. An improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.

Seasonal changes of CO2, CH4 and N2O fluxes in different types of alpine grassland in the Qinghai-Tibetan Plateau of China

Grassland degradation and grassland use type changes are associated with dynamics in soil properties and biogeochemical cycling, with implications for carbon and nitrogen cycling and trace gas fluxes. To examine the influence of grassland degradation and grassland use type changes on gases fluxes, emissions of CO2, CH4 and N2O were measured in three alpine ecosystems (alpine meadow, alpine steppe and alpine desert) with healthy and degraded grasslands on the Qinghai-Tibetan Plateau in May, August and October 2013. The lowest CO2, CH4 and N2O fluxes occurred in alpine deserts, and the highest fluxes occurred in alpine steppe. In general, degraded grasslands had relatively higher gas fluxes than healthy grasslands, except for CH4 dynamics. The temporal variation in gas fluxes indicated that CO2 and N2O fluxes were highest in August and lowest in May, while the lowest fluxes of CH4 were in August. Stepwise linear analysis was employed to explore the key factors for different gas fluxes. In alpine meadow and alpine steppe, the variation in CO2 and N2O fluxes in August could be explained by soil temperature and soil water content, while in May and October, soil physical and chemical properties, including soil pH, clay content and NO3-–N, were the key factors. Soil water content and NH4+–N contributed to the CH4 fluxes. However, in alpine desert, soil water content was the key factor affecting gas emissions for different experimental sites. These results indicate that the examined alpine grasslands emitted a large amount of gas emissions especially after the grassland had degraded; therefore, more attention should be paid to protecting grassland degradation in the Qinghai-Tibetan Plateau.

Variation and control of soil organic carbon and other nutrients in permafrost regions on central Qinghai-Tibetan Plateau

The variation and control of soil organic carbon (SOC) and other nutrients in permafrost regions are critical for studying the carbon cycle and its potential feedbacks to climate change; however, they are poorly understood. Soil nutrients samples at depths of 0–10, 10–20, 20–30, and 30–40 cm, were sampled eight times in 2009 in alpine swamp meadow, alpine meadow and alpine steppe in permafrost regions of the central Qinghai-Tibetan Plateau. SOC and total nitrogen (TN) in the alpine swamp meadow and meadow decreased with soil depth, whereas the highest SOC content in the alpine steppe was found at depths of 20–30 cm. The vertical profiles of total and available phosphorus (P) and potassium (K) were relatively uniform for all the three grassland types. Correlation and linear regression analyses showed that soil moisture (SM) was the most important parameter for the vertical variation of SOC and other soil nutrients, and that belowground biomass (BGB) was the main source of SOC and TN. The spatial variations (including seasonal variation) of SOC and TN at plot scale were large. The relative deviation of SOC ranged from 7.18 to 41.50 in the alpine swamp meadow, from 2.88 to 35.91 in the alpine meadow, and from 9.33 to 68.38 in the alpine steppe. The spatial variations in the other soil nutrients varied among different grassland types. The most important factors for spatial variations (including seasonal variation) of SOC, TN, total P, available P, and both total and available K were: SM, SM and temperature, SM, air temperature, and SM and BGB, respectively. The large variation in the three grassland types implies that spatial variation at plot scale should be considered when estimating SOC storage and its dynamics.

Field evidence for earlier leaf-out dates in alpine grassland on the eastern Tibetan Plateau from 1990 to 2006.

Worldwide, many plant species are experiencing an earlier onset of spring phenophases due to climate warming. Rapid recent temperature increases on the Tibetan Plateau (TP) have triggered changes in the spring phenology of the local vegetation. However, remote sensing studies of the land surface phenology have reached conflicting interpretations about green-up patterns observed on the TP since the mid-1990s. We investigated this issue using field phenological observations from 1990 to 2006, for 11 dominant plants on the TP at the levels of species, families (Gramineae-grasses and Cyperaceae-sedges) and vegetation communities (alpine meadow and alpine steppe). We found a significant trend of earlier leaf-out dates for one species (Koeleria cristata). The leaf-out dates of both Gramineae and Cyperaceae had advanced (the latter significantly, starting an average of 9 days later per year than the former), but the correlation between them was significant. The leaf-out dates of both vegetation communities also advanced, but the pattern was only significant in the alpine meadow. This study provides the first field evidence of advancement in spring leaf phenology on the TP and suggests that the phenology of the alpine steppe can differ from that of the alpine meadow. These findings will be useful for understanding ecosystem responses to climate change and for grassland management on the TP.

A MODIS-based Photosynthetic Capacity Model to estimate gross primary production in Northern China and the Tibetan Plateau

Accurate quantification of the spatio-temporal variation of gross primary production (GPP) for terrestrial ecosystems is significant for ecosystem management and the study of the global carbon cycle. In this study, we propose a MODIS-based Photosynthetic Capacity Model (PCM) to estimate GPP in Northern China and the Tibetan Plateau. The PCM follows the logic of the light use efficiency model and is only driven by the Enhanced Vegetation Index (EVI) and the Land Surface Water Index (LSWI). Multi-year eddy CO2 flux data from five vegetation types in North China (temperate mixed forest, temperate steppe) and the Tibetan Plateau (alpine shrubland, alpine marsh and alpine meadow-steppe) were used for model parameterization and validation. In most cases, the seasonal and interannual variation in the simulated GPP agreed well with the observed GPP. Model comparisons showed that the predictive accuracy of the PCM was higher than that of the MODIS GPP products and was comparable with that of the Vegetation Photosynthesis Model (VPM) and the potential PAR-based GPP models. The model parameter (PCmax) of the PCM represents the maximum photosynthetic capacity, which showed a good linear relationship with the mean annual nighttime Land Surface Temperature (LSTan). With this linear function, the PCM-simulated GPP can explain approximately 93% of the variation in the flux-observed GPP across all five vegetation types. These analyses demonstrated the potential of the PCM as an alternative tool for regional GPP estimation.

青海省高寒草地土壤无机碳储量空间分异特征

PDF HTML阅读 XML下载 导出引用 引用提醒 青海省高寒草地土壤无机碳储量空间分异特征 DOI: 10.5846/stxb201301250156 作者: 作者单位: 中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（41030105）；中国科学院战略性先导科技专项（XDA05050404）（固碳现状、速率、机制和潜力）项目 The variation feature of soil inorganic carbon storage in alpine grassland in Qinghai province Author: Affiliation: Northwest Institute of Plateau biology, Chinese Academy of Sciences,,,,,,,,Northwest Institute of Plateau biology, Chinese Academy of Sciences 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:以青海省主要高寒草地类型即温性草原、高寒草原、草甸草原以及高寒草甸为研究对象，进行其土壤无机碳（SIC）储量分异特征研究。结果表明，在取样剖面内四类草地SIC储量依次为温性草原 >高寒草原 >草甸草原 >高寒草甸，其值分别为16.51、16.48 、3.37 kgC/m2和0.12 kgC/m2，温性草原与高寒草原土壤是高寒草地无机碳的主要储蓄库。温性草原与高寒草原50-100cm SIC储量分别占0-100cm总储量的60.2%和 51.8%，而草甸草原与高寒草甸30-50cmSIC储量分别占0-50cm总储量的50.1%和55.8%，说明土体下部是高寒草地无机碳储蓄的主要场所。四类草地SIC含量随土层深度的变化过程各异，其碳酸钙富集层与野外剖面调查所得碳酸钙盐酸泡沫检验结果相吻合。SIC储量与土壤容重和土壤pH均呈显著正相关关系，与地下生物量呈显著负相关关系。 Abstract:The warm steppe, alpine steppe, alpine meadow steppe and alpine meadow are the main grassland types which widely distribute in Qinghai-Tibetan plateau. It's widely distribution and diverse development environments make it play an important role in the ecosystem: supporting regional economic development, guaranteeing water conservation of the plateau, maintaining biodiversity, fixation of carbon, etc. A quantitative survey of the variation feature of soil inorganic carbon(SIC)stored in warm steppe, alpine steppe, alpine meadow steppe and alpine meadow were carried out in Qinghai province. Results showed that the total storage of SIC in the four types grassland appeared to be warm steppe> alpine steppe> meadow steppe> alpine meadow, and the values were 16.51kgC/m2,16.48 kgC/m2,3.37 kgC/m2 and 0.12 kgC/m2, respectively. One-Way ANOVA analysis indicated that warm steppe、alpine steppe had a significant difference with alpine meadow steppe and alpine meadow(P < 0.05)while no significant difference between warm steppe and alpine steppe as well as alpine meadow steppe and alpine meadow(P > 0.05). The warm steppe and alpine steppe grassland are the main reserve pool of SIC in alpine grassland. The SIC stored in 50-100cm accounted separately for 60.2% and 51.8% of the total storage in 0-100cm profile of the warm steppe and alpine steppe, while in alpine meadow steppe and alpine meadow, it occupied 50.1% and 55.8% respectively of the 30-50cm in 0-50cm. Deep soil layer is the main place of SIC storing in alpine grassland. Soil depth has an important effect on SIC storage in alpine grassland. In 0-50cm depth of the soil, SIC storing in the four types grassland were 6.57 kgC/m2,7.95 kgC/m2,3.37 kgC/m2 and 0.12 kgC/m2, respectively. The change of SIC content with soil depth were different in the four types grassland. It increased with soil depth in warm steppe and alpine meadow steppe, but increased at first then decreased in alpine meadow steppe and alpine meadow. The calcium carbonate enrichment layer in the soil tallied with the foam examination by hydrochloric acid in the soil profile investigation. The calcium carbonate accumulate in the deep soil of steppe, but enrich rather shallow in meadow. SIC storage in the four types of grassland had a significantly positive correlation with soil bulk density and pH value but a significantly negative correlation with underground biomass. The SIC storage increased from south to north in the grassland of Qinghai province and the total SIC storage of the four types grassland reached 1.34 Pg in the profile. The SIC storage in the alpine meadow is very small and it mainly distributed in the south of Qinghai province. Warm steppe which has the largest SIC storage mainly distributed nearby the Qinghai Lake. Climate change and human activity may affect the capacity and distribution of the carbon storage which would bring the ecological risk to the inorganic carbon fixation. 参考文献 相似文献 引证文献

Wind tunnel simulation and evaluation of soil conservation function of alpine grassland in Qinghai–Tibet Plateau

Aiming at studying soil conservation function of alpine grassland in the Qinghai–Tibet Plateau, this paper simulated soil erosion changes under different degrees of human disturbance in a wind tunnel laboratory. Three types of grasslands were selected, which include alpine meadow (QH-1), alpine steppe meadow (QH-2) and alpine steppe (QH-3), and the soil erosion rate was taken as the index to measure soil conservation function. The experimental results show that the soil erosion rates of three grassland samples increase with wind velocity under different treatments but the increment of erosion rate varied greatly. Under original status, soil erosion rates are in turn QH-1<QH-2<QH-3, which indicates that the soil conservation services are QH-1>QH-2>QH-3. When the aboveground vegetation was cut, the soil erosion rate change of QH-1 is the same as that of QH-3 and compared with the original status both of them changed a little. And when the root system was destroyed the erosion rates range in turn as QH-1<QH-2<QH-3. So the data suggest that soil conservation service for the three types of grasslands should be QH-1>QH-2>QH-3. The economic values of soil conservation were estimated, which include the values of organic carbon fixation, nutrient retention and reducing soil disuse.

Relationships between altitudinal gradient and plant carbon isotope composition of grassland communities on the Qinghai-Tibet Plateau, China

Foliar and root carbon isotope composition (δ13C) of grassland communities on the Qinghai-Tibet Plateau, China, was obtained by the biomass weighting method and direct measurement. We investigated the characteristics and altitudinal patterns of foliar and root δ13C and determined which environmental factors influenced foliar δ13C most. Foliar δ13C of alpine steppe was significantly higher than that of alpine meadow and temperate steppe. For alpine meadow, root δ13C was significantly higher than of foliar δ13C. Foliar δ13C increased with altitude at an average rate of 0.60‰ km−1 for the whole grassland ecosystem. This rate was lower than that at species level. However, there were no significant relationships between root δ13C and altitude. Atmospheric pressure was a more important factor than temperature and precipitation in its influence on the altitudinal pattern of foliar δ13C at the community level.

Effects of plateau pika (Ochotona curzoniae) on net ecosystem carbon exchange of grassland in the Three Rivers Headwaters region, Qinghai-Tibet, China

Because the indigenous burrowing lagomorph plateau pika (Ochotona curzoniae) is considered to have negative ecological impacts on alpine meadow steppe grasslands of the Headwaters Region of the Yellow, Yangtze and Mekong Rivers we investigated its effects on ecosystem productivity and soil properties, and especially net ecosystem carbon flux. We measured net ecosystem CO2 exchange (NEE) and its components gross ecosystem productivity (GEP) and ecosystem respiration (ER) at peak aboveground biomass by the chamber method with reference to plant and soil characteristics of areas of alpine meadow steppe with different densities of pika burrows. Higher burrow density decreased NEE, GEP and ER. Above-ground biomass, species number, plant cover and leaf area index decreased with increasing pika density. Higher burrow density was associated with lower soil moisture and higher soil temperature. Responses of NEE were related to changes of abiotic and biotic factors affecting its two components. NEE was positively related to soil moisture, soil ammonium nitrogen, plant cover, leaf area index and above-ground biomass but was negatively correlated with higher soil nitrate nitrogen. Decrease of NEE by plateau pika may reduce the carbon sink balance of Qinghai-Tibet plateau grassland. Such effects may be influenced by grazing pressure from domestic livestock, population levels of natural predators, and climate change.

Gross Nitrification and Denitrification in Alpine Grassland Ecosystems on the Tibetan Plateau

Nitrification and denitrification are key microbiological processes in the soil nitrogen cycle and are the main biological sources of N2O emissions from soils. In this work, we measured gross nitrification and denitrification rates of northern Tibet alpine grassland ecosystems during the growing season and evaluated the influence of soil environmental factors. The results showed that the soil inorganic nitrogen concentration and gross nitrification and denitrification rates of both alpine meadow and alpine steppe varied obviously across the season. During the growing season mean values of gross nitrification and denitrification rates of the alpine meadow site were 3.0 and 2.3 times greater than those of the alpine steppe site, respectively. Both gross nitrification and denitrification rates were not significantly correlated with the determined soil characteristics which include soil microbial biomass, inorganic nitrogen, and soil temperature, except that gross nitrification seemed associated with the microsite where soil moisture was higher. Our results demonstrate that soil moisture can explain partly the higher soil nitrogen (N) transformation rates in alpine meadow sites, but soil N transformation microorganisms and enzyme activities studies covering prolonged observation periods are still needed to clarify the key soil environmental factors that control gross nitrification and denitrification processes in alpine grassland ecosystems.

Soil water soluble organic carbon under three alpine grassland types in Northern Tibet, China

Water soluble organic carbon (WSOC) is the most mobile and reactive soil carbon sourceavailable. It plays an important role in many biogeochemical processes. In this study, we assessed WSOC in the upper 0 to 15 cm soil layer, during the growing season of three representative alpine grassland types of Northern Tibet, with an average elevation of over 4500 m. We also evaluated the contributions of soil environmental factors on the three types of grassland. We found that the WSOC was typically higher at the first sampling in May and decreased with subsequent samples. Furthermore, over the short growing season, the alpine meadow steppe ecosystem had significantly higher WSOC content than the alpine meadow and alpine steppe ecosystems. Soil WSOC of alpine grasslands also negatively correlated with both soil temperature and moisture. These results indicated that soil WSOC is considerably different among the different types of grassland in the same alpine area, and we conclude that soil environmental conditions including soil temperature and moisture are important influencing factors that control soil WSOC content. Key words: Water soluble organic carbon, soil temperature, soil moisture, alpine grassland, Northern Tibet.

Response of biomass spatial pattern of alpine vegetation to climate change in permafrost region of the Qinghai-Tibet Plateau, China

Alpine ecosystems in permafrost region are extremely sensitive to climate changes. To determine spatial pattern variations in alpine meadow and alpine steppe biomass dynamics in the permafrost region of the Qinghai-Tibet Plateau, China, calibrated with historical datasets of above-ground biomass production within the permafrost region’s two main ecosystems, an ecosystem-biomass model was developed by employing empirical spatialdistribution models of the study region’s precipitation, air temperature and soil temperature. This model was then successfully used to simulate the spatio-temporal variations in annual alpine ecosystem biomass production under climate change. For a 0.44°C decade-1 rise in air temperature, the model predicted that the biomasses of alpine meadow and alpine steppe remained roughly the same if annual precipitation increased by 8 mm per decade−1, but the biomasses were decreased by 2.7% and 2.4%, respectively if precipitation was constant. For a 2.2°C decade−1 rise in air temperature coupled with a 12 mm decade−1 rise in precipitation, the model predicted that the biomass of alpine meadow was unchanged or slightly increased, while that of alpine steppe was increased by 5.2%. However, in the absence of any rise in precipitation, the model predicted 6.8% and 4.6% declines in alpine meadow and alpine steppe biomasses, respectively. The response of alpine steppe biomass to the rising air temperatures and precipitation was significantly lesser and greater, respectively than that of alpine meadow biomass. A better understanding of the difference in alpine ecosystem biomass production under climate change is greatly significant with respect to the influence of climate change on the carbon and water cycles in the permafrost regions of the Qinghai-Tibet Plateau.