Qinghai-Tibetan Plateau Alpine Research Articles

Vegetation degradation and its progressive impact on soil nitrogen mineralization in the Qinghai-Tibet Plateau's alpine wetlands: Insights from a three-year study.

The soil nitrogen (N) cycle in the alpine wetland of the Qinghai-Tibet Plateau (QTP) has been strongly affected by vegetation degradation caused by climate change and human activities, subsequently impacting ecosystem functions. However, previous studies have rarely addressed how varying degrees of vegetation degradation affect soil net nitrogen mineralization rates and their temporal dynamics in these sensitive ecosystems. Therefore, we conducted a three-year field-based soil core in situ incubation mineralization experiment on the northeastern margin of the Tibetan Plateau from 2019 to 2021 to assess the variations in soil net ammonification, nitrification, and mineralization rates during the growing season (June to October). The main aim was to determine the dynamic effects of different degrees of vegetation degradation (non-degraded, lightly degraded, moderately degraded, and severely degraded) on soil net nitrogen transformation processes, as well as the impact of seasonal fluctuations in soil temperature and moisture on net nitrogen mineralization. Results indicated that vegetation degradation significantly reduced the net ammonification rate by 22.09%-97.10%, significantly increased the net nitrification rate by 45.38%, and significantly decreased the net mineralization rate by 9.49%-16.25%. Redundancy analysis (RDA) and random forest models revealed the supportive role of soil water content in the soil nitrogen transformation processes, particularly in promoting nitrification, while soil temperature was identified as a positive regulator of N cycling enzyme activity, indirectly affecting net nitrogen mineralization rates.

Regional differences in the impact paths of climate on aboveground biomass in alpine grasslands across the Qinghai-Tibet Plateau

Alpine grasslands on the Qinghai-Tibet Plateau (QTP) play an essential role in water conservation, biodiversity protection and climate feedback, with aboveground biomass (AGB) serving as a crucial indicator of grassland health and functionality. While previous studies have independently explored the phenological differences, cumulative effects, and spatial variability of climatic impacts on biomass/productivity in alpine grasslands, the cascading effects regarding climate and phenology on AGB still present knowledge gaps. Here, using peak AGB measurements, remote sensing and gridded climate data in the QTP alpine grasslands during 2002–2018, we systematically analyzed the impact paths of climatic variables (i.e., cumulative precipitation, CP; growing degree-days, GDD) and phenology-mediated paths (start and peak date of the growing season, SOS and POS) on AGB and their regional differences. During the preseason (pre60) or the growing season (sos-pos), climate primarily directly impacted variations in AGB across different climatic regions, although a phenology-mediated path by which climate indirectly affected AGB existed (i.e., GDDsos-pos → POS → AGB). Three general patterns were revealed: In the plateau temperate arid regions, an increase in CPpre60 significantly promoted AGB (path coefficients w = 0.61–0.71), whereas an increase in GDDpre60 inhibited AGB (w = −0.42 ~ −0.49); In the plateau sub-cold regions, increases in both CPsos-pos and GDDsos-pos significantly promoted AGB, respectively (w = 0.46–0.81 and w = 0.37–0.70); Similarly, in the plateau temperate arid or semi-arid regions, increases in CPsos-pos also significantly promoted the AGB (w = 0.56–0.73). This study highlights that the water and heat accumulation mainly exert direct impacts on alpine grassland AGB across various climatic regions and phenological stages, providing insights into the mechanism driving AGB by climate and phenology during spring and summer.

Identification and validation of stable reference genes for RT-qPCR analyses of Kobresia littledalei seedlings

BackgroundKobreisa littledalei, belonging to the Cyperaceae family is the first Kobresia species with a reference genome and the most dominant species in Qinghai-Tibet Plateau alpine meadows. It has several resistance genes which could be used to breed improved crop varieties. Reverse Transcription Quantitative Real-Time Polymerase Chain Reaction (RT-qPCR) is a popular and accurate gene expression analysis method. Its reliability depends on the expression levels of reference genes, which vary by species, tissues and environments. However, K.littledalei lacks a stable and normalized reference gene for RT-qPCR analysis.ResultsThe stability of 13 potential reference genes was tested and the stable reference genes were selected for RT-qPCR normalization for the expression analysis in the different tissues of K. littledalei under two abiotic stresses (salt and drought) and two hormonal treatments (abscisic acid (ABA) and gibberellin (GA)). Five algorithms were used to assess the stability of putative reference genes. The results showed a variation amongst the methods, and the same reference genes showed tissue expression differences under the same conditions. The stability of combining two reference genes was better than a single one. The expression levels of ACTIN were stable in leaves and stems under normal conditions, in leaves under drought stress and in roots under ABA treatment. The expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression was stable in the roots under the control conditions and salt stress and in stems exposed to drought stress. Expression levels of superoxide dismutase (SOD) were stable in stems of ABA-treated plants and in the roots under drought stress. Moreover, RPL6 expression was stable in the leaves and stems under salt stress and in the stems of the GA-treated plants. EF1-alpha expression was stable in leaves under ABA and GA treatments. The expression levels of 28 S were stable in the roots under GA treatment. In general, ACTIN and GAPDH could be employed as housekeeping genes for K. littledalei under different treatments.ConclusionThis study identified the best RT-qPCR reference genes for different K. littledalei tissues under five experimental conditions. ACTIN and GAPDH genes can be employed as the ideal housekeeping genes for expression analysis under different conditions. This is the first study to investigate the stable reference genes for normalized gene expression analysis of K. littledalei under different conditions. The results could aid molecular biology and gene function research on Kobresia and other related species.

Effect of foraging tunnels created by small subterranean mammals on soil microbial biomass carbon and organic carbon storage in alpine grasslands

Extensive foraging tunnel disturbances created by small subterranean mammals have important impacts on soil physical properties and nutrients in grasslands. This study took plateau zokor (Eospalax baileyi) as an example mammal to investigate the impacts of foraging tunnel disturbances by small subterranean mammals on soil microbial biomass carbon (SMBC) and soil organic carbon (SOC) storage. A paired design was used to locate 90 tunnel quadrats and 90 non-tunnel quadrats in alpine grasslands across three sites. This study showed that SMBC, SOC concentrations and SOC storage in tunnel quadrats were 47.4 %, 26.8 % and 22.0 % lower than those in non-tunnel quadrats, respectively. This study also showed that soil microbial biomass nitrogen was a major factor affecting SOC storage in non-tunnel quadrats, while it was not a major factor in tunnel quadrats. Soil pH and soil ammonium nitrogen were not major factors in non-tunnel quadrats, while they were the major factors influencing SOC storage in tunnel quadrats. In contrast to non-tunnel quadrats, foraging tunnel disturbances led to a new pathway in which soil pH positively affected SOC storage in tunnel quadrats. The findings of this study demonstrated that foraging tunnel disturbances had negative impacts on soil fertility due to lower SMBC concentrations and might cause soil carbon loss in alpine grasslands because of lower SOC storage. Given the effect of foraging tunnels on soil carbon cycling and climate regulation in the Qinghai-Tibet Plateau's alpine grasslands, it is crucial to take them into account when assessing grassland carbon storage and formulating strategies for effective grassland management and conservation.

A 2020 forest age map for China with 30 m resolution

Abstract. A high-resolution, spatially explicit forest age map is essential for quantifying forest carbon stocks and carbon sequestration potential. Prior attempts to estimate forest age on a national scale in China have been limited by sparse resolution and incomplete coverage of forest ecosystems, attributed to complex species composition, extensive forest areas, insufficient field measurements, and inadequate methods. To address these challenges, we developed a framework that combines machine learning algorithms (MLAs) and remote sensing time series analysis for estimating the age of China's forests. Initially, we identify and develop the optimal MLAs for forest age estimation across various vegetation divisions based on forest height, climate, terrain, soil, and forest-age field measurements, utilizing these MLAs to ascertain forest age information. Subsequently, we apply the LandTrendr time series analysis to detect forest disturbances from 1985 to 2020, with the time since the last disturbance serving as a proxy for forest age. Ultimately, the forest age data derived from LandTrendr are integrated with the result of MLAs to produce the 2020 forest age map of China. Validation against independent field plots yielded an R2 ranging from 0.51 to 0.63. On a national scale, the average forest age is 56.1 years (standard deviation of 32.7 years). The Qinghai–Tibet Plateau alpine vegetation zone possesses the oldest forest with an average of 138.0 years, whereas the forest in the warm temperate deciduous-broadleaf forest vegetation zone averages only 28.5 years. This 30 m-resolution forest age map offers crucial insights for comprehensively understanding the ecological benefits of China's forests and to sustainably manage China's forest resources. The map is available at https://doi.org/10.5281/zenodo.8354262 (Cheng et al., 2023a).

Grazing practices affect soil microbial networks but not diversity and composition in alpine meadows of northeastern Qinghai-Tibetan plateau

Livestock grazing is the primary practice in alpine meadows and can alter soil microbiomes, which is critical for ecosystem functions and services. Seasonal grazing (SG) and continuous grazing (CG) are two kinds of different grazing practices that dominate alpine meadows on the Qinghai-Tibetan Plateau (QTP), and how they affect soil microbial communities remains in-depth exploration. The present study was conducted to investigate the effects of different grazing practices (i.e., SG and CG) on the diversity, composition, and co-occurrence networks of soil bacteria and fungi in QTP alpine meadows. Soil microbial α- and β-diversity showed no obvious difference between SG and CG grasslands. Grazing practices had little impact on soil microbial composition, except that the relative abundance of Proteobacteria and Ascomycota showed significant difference between SG and CG grasslands. Soil microbial networks were more complex and less stable in SG grasslands than that in CG grasslands, and the bacterial networks were more complex than fungal networks. Soil fungal diversity was more strongly correlated with environmental factors than bacteria, whereas both fungal and bacterial structures were mainly influenced by soil pH, total nitrogen, and ammonium nitrogen. These findings indicate that microbial associations are more sensitive to grazing practices than microbial diversity and composition, and that SG may be a better grazing practice for ecological benefits in alpine meadows.

Altitude restricts the restoration of community composition and vegetation coverage of quarries on the Qinghai-Tibet Plateau

It is challenging to restore Tibetan Plateau vegetation once it has been damaged.Highway construction, necessary for economic development, have significant negative impacts on the composition, structure, and functioning of the Qinghai-Tibet Plateau alpine grassland ecosystem. However, there is uncertainty regarding the extent of ecosystem damage in this region, such as whether quarries dug during highway construction may be restored and how recovery varies with increasing altitude. We conducted a transect survey of 39 quarry-restored grasslands reseeded with Elymus nutans and adjacent paired natural grasslands on the Gongyu and S308 highways on the Qinghai-Tibet Plateau (2800–5100 m above sea level). By comparing the community height, coverage, and species composition between restored and natural grasslands, we evaluated the degree of recovery and altitudinal gradient pattern of the grassland community and explained the limiting factors that led to the differences in recovery. After two-year restoration, quarry coverage and species composition were not restored to the degree of natural grassland. As altitude increased, the coverage recovery degree of quarry recovery community continued to decline, and the dissimilarity of community composition between the restored and natural grasslands was rising. We showed a breaking point at ca. 4100 m where recovery degree dropped dramatically, indicating a threshold for highway construction. The soil nutrients in quarry decreased significantly with increasing altitude. Structural equation modelling indicated that increasing altitude decreased the coverage of quarry by reducing temperature and soil nutrients. Due to the limitations of single species sowing, low temperature and nutrient availability, the effect of recovery decreased with increasing altitude. Therefore, we propose that during highway construction in the permafrost of the Qinghai-Tibet Plateau, quarries should avoid operation at high altitudes. When the altitude exceeds a certain height (e.g., 4100 m in this study), we do not recommend excavating quarries to destroy alpine grasslands.

Driving Climatic Factors at Critical Plant Developmental Stages for Qinghai–Tibet Plateau Alpine Grassland Productivity

Determining the driving climatic factors at critical periods and potential legacy effects is crucial for grassland productivity predictions on the Qinghai–Tibet Plateau (QTP). However, studies with limited and ex situ ground samples from highly heterogeneous alpine meadows brought great uncertainties. This study determined the key climatic factors at critical plant developmental stages and the impact of previous plant growth status for interannual aboveground net primary productivity (ANPP) variations in different QTP grassland types. We hypothesize that the impact of climatic factors on grassland productivity varies in different periods and different vegetation types, while its legacy effects are not great. Pixel-based partial least squares regression was used to associate interannual ANPP with precipitation and air temperature at different developmental stages and prior-year ANPP from 2000 to 2019 using remote sensing techniques. Results indicated different findings from previous studies. Precipitation at the reproductive stage (July–August) was the most prominent controlling factor for ANPP which was also significantly affected by precipitation and temperature at the withering (September–October) and dormant stage (November–February), respectively. The influence of precipitation was more significant in alpine meadows than in alpine steppes, while the differentiated responses to climatic factors were attributed to differences in water consumption at different developmental stages induced by leaf area changes, bud sprouting, growth, and protection from frost damage. The prior-year ANPP showed a non-significant impact on ANPP of current year, except for alpine steppes, and this impact was much less than that of current-year climatic factors, which may be attributed to the reduced annual ANPP variations related to the inter-annual carbon circulation of alpine perennial herbaceous plants and diverse root/shoot ratios in different vegetation types. These findings can assist in improving the interannual ANPP predictions on the QTP under global climate change.

高寒草甸生态系统降雨事件对不同深度土壤碳释放的试验分析

PDF HTML阅读 XML下载 导出引用 引用提醒 高寒草甸生态系统降雨事件对不同深度土壤碳释放的试验分析 DOI: 10.5846/stxb202010312791 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（41730854） Experimental analysis of soil carbon release at different depths by rainfall events in alpine meadow ecosystem Author: Affiliation: Fund Project: National Natural Science Foundation of China (41730854) 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:以青藏高原高寒草甸生态系统为研究对象，基于LI-8150土壤CO2通量全自动连续测量系统及实验设计，对不同深度的土壤碳释放进行了连续原位观测，分析了晴天和5次持续性降水条件下不同深度土壤碳释放特征，结合土壤温湿度的观测，解析了降雨对不同深度土壤碳释放的影响及机理。结果表明：（1）在0 cm、20 cm、40 cm、70 cm深度处，土壤碳释放均呈现明显的单峰曲线变化特征，其日均值（±标准差）分别为（3.96±0.89）μmol m-2 s-1、（5.09±1.79）μmol m-2 s-1、（7.83±1.95）μmol m-2 s-1和（4.43±1.6）μmol m-2 s-1。（2）降雨提高了土壤含水量，显著抑制了土壤碳释放，且对深层的抑制作用显著大于表层。其中，第5次持续性降水事件对土壤水分的补充作用最明显（增量最大），其对土壤碳释放的抑制作用也更显著，并出现负通量（即碳吸收）。随着土壤深度的增加，观测到碳吸收现象愈加显著。（3）不同深度土壤碳释放与土壤温度、水分呈指数或二次曲线相关关系。晴天条件下，土壤含水量较稳定，土壤温度是影响各层土壤碳释放的主导因子；而降雨条件下，土壤含水量变化显著，土壤水分成为主导土壤碳释放的关键因子，并对其可能产生的机理进行了讨论。 Abstract:This study selected Qinghai-Tibet Plateau alpine meadow ecosystem as the research object. Based on the Li-8150 automated soil CO2 flux system, continuous in-situ observation of soil carbon release at different depths was carried out, and the characteristics of soil carbon release at different depths in sunny and 5 times of continuous rain events were analyzed. Combined with the observation of soil temperature and soil moisture, the effects of rainfall on soil carbon release at different depths and possible mechanisms were analyzed. The results showed that, (1) The soil respiration at 0 cm, 20 cm, 40 cm, and 70 cm all showed obvious single-peak curve, and their daily average soil respiration (±standard deviation) were (3.96±0.89) μmol m-2 s-1, (5.09±1.79) μmol m-2 s-1, (7.83±1.95) μmol m-2 s-1 and (4.43±1.6) μmol m-2 s-1. (2) Rainfall significantly increased soil moisture, and inhibited soil carbon release, and the inhibition effects of deep layer was significantly greater than that of surface layer. Among them, the fifth persistent rain event had the most obvious supplementary effect on soil moisture (the largest increment), and its inhibitory effect on soil carbon release was also more significant, even negative flux (i.e., carbon sequestration) appeared in the deep layer. With the increase of soil depth, carbon absorption was observed to be more significant. (3) The relationship between soil carbon release at different depths and soil temperature or soil moisture was correlated with the exponential correlation or quadratic curve. Under sunny conditions, the soil moisture is stable, and the soil temperature is the dominate factor to affect the surface soil respiration. While under rainfall days, soil moisture changed significantly, and became the control of soil carbon release, and its possible mechanism was discussed. 参考文献 相似文献 引证文献

Spatiotemporal differences in climate change impacts on vegetation cover in China from 1982 to 2015.

The impacts of climate change on vegetation cover in different regions in China are not entirely clear because of the interference of non-climatic factors, such as human activity. This study aims to analyze the spatiotemporal differences in climate impacts qualitatively and quantitatively by applying trend, correlation, and multiple linear regression (MLR) analyses to the data of Normalized Difference Vegetation Index (NDVI) and two climatic factors (air temperature and precipitation) during 1982-2015 in China. The MLR equation linking two climatic variables with NDVI was used to identify the NDVI trend caused by climate change. We demonstrated that the central and eastern regions of China, dominated by deciduous and evergreen broadleaf forests, experienced a rapid increase in NDVI from 1982 to 2015. The response of NDVI to variations in temperature and precipitation exhibited large spatiotemporal differences across China, which was closely related to climatic conditions and vegetation types. Overall, warming, particularly the sharp rise in spring, was the main climatic driving force behind China's NDVI increase, and precipitation also influenced the NDVI increase in temperate grassland and desert regions due to the relatively arid climate, particularly in summer. The contributions of climate change to the total NDVI trend (CC) showed a large spatiotemporal heterogeneity across China. Overall, only 45% of the pixels (with a resolution of 8 km) in the study area showed that the MLR equations between NDVI and two climatic factors were significant at the 0.05 significance level during the growing season (April-October), and the average CC of these pixels was 38%. Among the eight vegetation sub-regions of China, the temperate desert and Qinghai-Tibet Plateau alpine meadow regions generally exhibited relatively larger CCs than other vegetation sub-regions in different seasons. At a national scale, the regional average CC reached 64% during the growing season. These results at multiple scales can help to deeply understand the mechanisms of regional environmental variation and sustainability.

Nitrogen Addition and Arbuscular Mycorrhizal Fungi Beta Diversity: Patterns and Mechanisms

Global nitrogen eutrophication, which is disrupting the intimate plant–arbuscular mycorrhizal fungi (AMF) symbiosis, can alter the diversity and physiological functions of soil AMF greatly. However, shifts of beta diversity and the intrinsic patterns of AMF community dissimilarities in response to nitrogen addition remain unclear. Based on a 7-year nitrogen addition experiment in a Qinghai–Tibet Plateau alpine meadow, we detected the changes in soil AMF alpha diversity (richness and genus abundance) and the community composition beta diversity by partitioning the two components of Simpson and nestedness dissimilarities along (turnover) and within (variation) nitrogen addition treatments, and fitted with environmental factor dissimilarities. We found that nitrogen addition decreased AMF richness by decreasing the most dominant AMF genus of Glomus but increasing the abundance of the rare genera. The turnover of the AMF community overall beta diversity along the nitrogen addition gradients was induced by the increased nestedness dissimilarity, while the variation within treatments was explained by both increased Simpson and nestedness dissimilarities, which was significantly correlated with soil pH. Our study found both Simpson and nestedness dissimilarities worked on the AMF community dissimilarity after nitrogen addition and the significant variation within the same treatment, which would be important in the future for predicting global AMF or microbial diversity changes in response to nitrogen eutrophication.

Aridity and NPP constrain contribution of microbial necromass to soil organic carbon in the Qinghai-Tibet alpine grasslands

Microbial necromass carbon (MNC) is key to soil organic carbon (SOC) storage. However, mechanisms regulating MNC accumulation on large scales are poorly understood. Here we provide the first batch of regional-scale MNC data based on amino sugars for the Qinghai-Tibet Plateau alpine grasslands. We show that Qinghai-Tibet grasslands have similar microbial biomass carbon (MBC) but lower MNC concentrations in SOC than Mongolian and other grasslands. The low contribution of MNC to SOC is mainly attributed to high aridity and low net primary productivity of the Qinghai-Tibet grasslands. Our findings highlight climatic and plant influences on MNC accumulation at regional scales.

A comparison of seed plants’ polyploids between the Qinghai-Tibet Plateau alpine and the Pan-Arctic regions

A comparison of seed plants’ polyploids between the Qinghai-Tibet Plateau alpine and the Pan-Arctic regions

NDVI Variations and Its Responses to hydrothermal process in the Naqu River Basin, Qinghai-Tibet Plateau-Alpine Region

Extensive studies have been conducted over the whole year and various seasons to characterize the temporal and spatial changes in vegetation NDVI. However, there are few studies on the variations of NDVI in different soil hydrothermal processes of the alpine region. So we studied the spatial-temporal variation of vegetation cover and its responses to hydrothermal process in the Qinghai-Tibet Plateau-alpine region. Based on the GIMMS NDVI remote sensing images from 1982 to 2015, the temporal and spatial variations of NDVI in the Naqu river basin at different time scales were studied by using maximum synthesis method, and the linear regression. Results show that the vegetation has an overall degradation trend in the Naqu river basin, with primarily moderate and mild degradation degrees. Completely freezing period, completely melting period and freezing process period are the main vegetation degradation periods.

Precipitation and temperature regulate the carbon allocation process in alpine wetlands: quantitative simulation

The quantitative study for the allocation of photosynthetically fixed carbon to plant tissues, soil, and respiratory losses is essential for understanding the key process of carbon (C) cycle. In this study, the measured C flux data was used to validate a process-based denitrification-decomposition (DNDC) model, and the C budget components were simulated and quantitatively separated in the Qinghai-Tibet Plateau alpine wetland ecosystem. The field observation and 50-year climate data in this site were used as input to simulate soil environment change, plant growth, and C allocation for DNDC. The local parameterization, optimization, calibration, and evaluation of the process-based DNDC model were conducted to improve the simulation accuracy of the model and to separate the C budget components of the Zoige alpine wetland ecosystem on the basis of measured C flux data. The results show that the modeled and measured values have good consistency on multiple time scales, and the system shows obvious C sink (− 169.16 g C m−2 yr−1). The plant net primary productivity (NPP) accounted for 53% of gross primary productivity (GPP); the plant autotrophic respiration (Ra) accounts for 61% of ecosystem respiration (Re); and the soil heterotrophic respiration (Rh) accounts for 51% of soil respiration (Rs). Vegetation has the strongest photosynthesis and net C sequestration capacity during the peak growth stage, while the system appears as a C source in the senescence stage. Moreover, Ra dominated during the first four periods of plant growth, while Rh was dominant in the plant senescence stage. There was a negative correlation between environmental factors and NEE and a significant positive relationship with other C budget variables (P < 0.001). Precipitation and temperature regulate the C budgets and C distribution. When soil temperature and monthly precipitation exceeded 7 °C and 18 mm mon−1, the ecosystem switched from C source to C sink. The optimized DNDC model can capture the dynamics of C budget in Zoige alpine wetland, and there are large differences in the function of C source and sink, C allocation, and relative contribution during different plant growth stages. Our work will provide support to predict the changes in C cycle components at regional scales in future climate change scenarios and to formulate measures to mitigate greenhouse effects.

Draft Genome Assembly of Floccularia luteovirens, an Edible and Symbiotic Mushroom on Qinghai-Tibet Plateau.

Floccularia luteovirens, also known as “Yellow mushroom”, is an edible ectomycorrhizal fungus widely distributed in the Qinghai-Tibet Plateau alpine meadow. So far, little genomic information is known about F. luteovirens, which is not conductive to the protection and utilization of it. In this manuscript, we present a first draft genome assembly and annotation of F. luteovirens. The fruiting body of F. luteovirens was sequenced with PacBio Sequel and Illumina Hiseq 2500 system. The assembled genome size was 28.8 Mb, and comprising 183 contigs with a N50 contig size of 571 kb. A total of 8,333 protein-coding genes were predicted and 7,999 genes were further assigned to different public protein databases. Besides, 400 CAZymes were identified in F. luteovirens. Phylogenetic analysis suggested that F. luteovirens should belong to the Agaricaceae family. Time tree result showed that the speciation of F. luteovirens happened approximately 170 Million years ago. Furthermore, 357 species-specific gene families were annotated against KEGG and GO database. This genome assembly and annotation should be an essential genomic foundation for understanding the phylogenetic, metabolic and symbiotic traits of F. luteovirens.

Precipitation and Minimum Temperature are Primary Climatic Controls of Alpine Grassland Autumn Phenology on the Qinghai-Tibet Plateau

Autumn phenology is a crucial indicator for identifying the alpine grassland growing season’s end date on the Qinghai-Tibet Plateau (QTP), which intensely controls biogeochemical cycles in this ecosystem. Although autumn phenology is thought to be mainly influenced by the preseason temperature, precipitation, and insolation in alpine grasslands, the relative contributions of these climatic factors on the QTP remain uncertain. To quantify the impacts of climatic factors on autumn phenology, we built stepwise linear regression models for 91 meteorological stations on the QTP using in situ herb brown-off dates, remotely sensed autumn phenological metrics, and a multi-factor climate dataset during an optimum length period. The results show that autumn precipitation has the most extensive influence on interannual variation in alpine grassland autumn phenology. On average, a 10 mm increase in autumn precipitation during the optimum length period may lead to a delay of 0.2 to 4 days in the middle senescence date (P &lt; 0.05) across the alpine grasslands. The daily minimum air temperature is the second most important controlling factor, namely, a 1 °C increase in the mean autumn minimum temperature during the optimum length period may induce a delay of 1.6 to 9.3 days in the middle senescence date (P &lt; 0.05) across the alpine grasslands. Sunshine duration is the third extensive controlling factor. However, its influence is spatially limited. Moreover, the relative humidity and wind speed also have strong influences at a few stations. Further analysis indicates that the autumn phenology at stations with less autumn precipitation is more sensitive to precipitation variation than at stations with more autumn precipitation. This implies that autumn drought in arid regions would intensely accelerate the leaf senescence of alpine grasslands. This study suggests that precipitation should be considered for improving process-based autumn phenology models in QTP alpine grasslands.

Population subdivision and hybridization in a species complex of Gentiana in the Qinghai-Tibetan Plateau.

Hosting several global biodiversity hotspots, the region of the Qinghai-Tibetan Plateau (QTP) is exceptionally species-rich and harbours a remarkable level of endemism. Yet, despite a growing number of studies, factors fostering divergence, speciation and ultimately diversity remain poorly understood for QTP alpine plants. This is particularly the case for the role of hybridization. Here, we explored the evolutionary history of three closely related Gentiana endemic species, and tested whether our results supported the mountain geo-biodiversity hypothesis (MGH). We genotyped 69 populations across the QTP with one chloroplast marker and 12 nuclear microsatellite loci. We performed phylogeographical analysis, Bayesian clustering, approximate Bayesian computation and principal components analysis to explore their genetic relationship and evolutionary history. In addition, we modelled their distribution under different climates. Each species was composed of two geographically distinct clades, corresponding to the south-eastern and north-western parts of their distribution. Thus Gentiana veitchiorum and G. lawrencei var. farreri, which diverged recently, appear to have shared at least refugia in the past, from which their range expanded later on. Indeed, climatic niche modelling showed that both species went through continuous expansion from the Last Interglacial Maximum to the present day. Moreover, we have evidence of hybridization in the northwest clade of G. lawrencei var. farreri, which probably occurred in the refugium located on the plateau platform. Furthermore, phylogenetic and population genetic analyses suggested that G. dolichocalyx should be a geographically limited distinct species with low genetic differentiation from G. lawrencei var. farreri. Climatic fluctuations in the region of the QTP have played an important role in shaping the current genetic structure of G. lawrencei var. farreri and G. veitchiorum. We argue that a species pump effect did occur prior to the Last Interglacial Maximum, thus lending support to the MGH. However, our results do depart from expectations as suggested in the MGH for more recent distribution range and hybridization dynamics.

Effects of Litter Leachate on Plant Community Characteristics of Alpine Grassland in Qinghai Tibetan Plateau

Plant litter dynamics are sensitive to grassland productivity and the spatial heterogeneity of plant community. In this study, we investigated the effects of litter leachates on plant community characteristics using three plant species that represent different successional stages of alpine grasslands located on the Qinghai-Tibetan Plateau (QTP). We tested four concentrations of leachates (0, 50, 100, and 200 g L−1) from Kobresia setchwanensis, Elymus nutans, and Ligularia virgaurea. The leachates from the three plant species generally responded similarly, but the responses to the varying concentrations were significantly different. Addition of litter leachates negatively impacted the aboveground biomass and species richness. The Shannon-Wiener diversity index was positively correlated with the litter leachate addition. The effects of the litter leachate’s addition on plant functional groups varied—grasses were inhibited, forbs and legumes were promoted, and sedges were not significantly affected. This study demonstrates that litter leachates are a critical determinant of species diversity, grassland productivity, and community structure in QTP alpine grasslands.

Characteristics of soil enzyme stoichiometry along an altitude gradient on Qinghai-Tibet Pla-teau alpine meadow, China

Soil enzymes play critical roles in material cycle and energy flow of ecosystems. Understanding soil enzyme activities is of great significance for exploring ecosystem functions. In this study, we investigated soil enzyme activities, stoichiometry and their driving factors at six different altitudes (4300-5100 m) on Qinghai-Tibet Plateau alpine meadow using Biolog microplate analysis. The results showed that β-1,4-glucosidase (βG) closely related to C cycle, β-1,4-N-acetylglucosaminidase (NAG) and L-leucine aminopeptidase (LAP) closely related to N cycle and the activity of acid phosphatase (AP), which was closely related to P cycle, all exhibited unimodal trends with increasing altitude, with the order of 4800 m＞4950 m＞4400 m＞4650 m＞5100 m＞4300 m. Soil N:P enzyme activity ratio showed the same trend as soil enzyme activity, and reached the highest value at 4950 m, however, soil C:N and C:P enzyme activities ratios increased along the altitude. Pearson correlation analysis showed that SOC, TN and soil water content were significantly positively correlated with the activities of four types of enzymes. Mean annual precipitation was significantly negatively associated with the activities of NAG and AP. Mean annual precipitation, mean annual temperature, Shannon diversity, vegetation richness, vegetation coverage and TN affected ratios of soil C:P and N:P enzymes. Soil C:N activity ratio correlated with mean annual temperature, mean annual precipitation, vegetation richness, vegetation coverage, SOC and TN. In summary, soil enzyme activities and stoichiometry had remarkable difference along the altitude gradient on Qinghai-Tibet Plateau alpine meadow, with certain N limitation in high altitude areas. Soil water content, TN, SOC, mean annual precipitation and mean annual temperature were key factors driving such differences.