Degraded Alpine Meadow Research Articles

Characterization of the Plant‒Soil feedback index in alpine meadow degradation and recovery: A field experiment

Most plant‒soil feedback studies have been conducted on the mechanism by which soil directly influences plant growth performance and mostly in indoor pot experiments; however, it is unclear how plant‒soil feedback is influenced by plant, soil and microbial diversity in grassland ecosystems in alpine meadows with high plant diversity. In this study, plant‒soil feedback patterns were investigated by analyzing plant, soil and microbial characteristics across seven gradients in the time series from light degradation to 10-years of recovery, classified into three categories: ecosystem multifunctionality, biotic and abiotic factors, and comparing the strength and magnitude of plant‒soil feedback in alpine meadows of degradation stages and years of recovery. The results showed that the plant-soil feedback relationships in alpine meadows differed significantly in three aspects: ecosystem multifunctionality, biotic and abiotic factors in the degradation stage and recovery years, and under the degradation gradient, ecosystem multifunctionality decreased from 0.34 to −0.99 with the deepening of degradation, biotic factors increased from −0.17 to 0.09, and abiotic factors increased from −0.17 to 0.15, while in the recovery gradient, ecosystem multifunctionality showed a trend of increasing and then decreasing with increasing recovery years, while biotic and abiotic factors showed fluctuating changes. The plant-soil feedback index indicated that the strength and direction of plant-soil interactions during degradation and recovery were different, and the positive feedback effect was 0.34 and 0.38 in the early stage of degradation and recovery, respectively, which were greater than the negative feedback effect. With the deepening of degradation, the negative feedback effect became more and more obvious, and at the stage of extreme degradation, the negative feedback effect reached −0.99, which was much larger than the positive feedback effect. However, with the increase of the recovery years, the positive feedback effect gradually weakened, and finally all of them were negative feedback effects at 10-years of recovery. This study provides a scientific basis for understanding plant-soil feedback in alpine meadow ecosystems and indicates the direction for the next scientific recovery of alpine meadows.

Watershed-level spatial pattern of degraded alpine meadow and its key influencing factors in the Yellow River Source Zone of West China

This study aims to characterize the watershed-level distribution patterns of severely degraded alpine meadows commonly known as “heitutan” in the Yongqu River basin of the Source Zone of Yellow River. Topographic data were analyzed in ArcGIS to derive several variables and delineate multi-level watershed units. In addition, remotely sensed data were analyzed to map ground covers in two-level watershed units (i.e. first-level and second-level watershed units), including heitutan degraded grassland. The two sets of results were intersected to identify the correlation of land covers and spatial proximity with heitutan and their possible influences on it. The results show that the alpine meadow in the Yongqu watershed comprised 51.39 % of the total area, and shrub grassland accounted for 45.45 % of the total area. At the first-level tributary unit of the Yongqu watershed, heitutan-degraded grassland is the most common feature at 4.75 km2, accounting for 2.46 % of all alpine meadows. Heitutan patches on average have a minimal size of 1007 m2. Most heitutan patches are distributed on gentle, mainly sunny, and semi-sunny slopes of 7–18° in gradient. They are situated within 1000 m of roads, accounting for 90.53 % of total “heitutan”, while 96.56 % are distributed within 0–1500 m of settlements. At the second-level tributary unit of the Hallaqu and Chayangwa, heitutan is the most common at 1.23 and 0.41 km2, respectively, accounting for 0.79 % and 1.01 % of the total alpine meadows. However, the highest proportion in the Chayangwa River basin is in the 0–3° beach areas. The areas widely distributed with heitutan heavily overlap with those affected by overgrazing and rodent activities. Redundancy analysis and structural equation modeling indicate that slope exerts the greatest influence on the formation and distribution patterns of the heitutan degraded grassland, followed by slope aspect and distance to roads. In comparison, distance to river channels and settlements and the annual temperature has an insignificant influence on the heitutan degraded grassland.

高原鼠兔和高原鼢鼠种群暴发区干扰斑块空间分布格局与演替规律

PDF HTML阅读 XML下载 导出引用 引用提醒 高原鼠兔和高原鼢鼠种群暴发区干扰斑块空间分布格局与演替规律 DOI: 10.5846/stxb202204161021 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31872999，U21A20191）；青海省科学技术厅项目（2020-ZJ-904）；高等学校学科创新引智计划（D18013） Spatial distribution pattern and succession of disturbance patches formed by plateau pika and plateau zokor in their population outbreak areas in alpine meadow 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:高原鼠兔（Ochotona curzoniae）和高原鼢鼠（Myospalax baileyi）是两种在高寒草甸广泛分布的小型哺乳动物，其暴发活动可能造成高寒草甸的严重退化。使用无人机分别拍摄典型的高原鼠兔和高原鼢鼠种群暴发区图像，解译高原鼠兔洞口、高原鼢鼠土丘和它们的干扰斑块，获得干扰斑块的周长和面积信息，计算干扰斑块形状指标，确定高原鼠兔与高原鼢鼠暴发活动对高寒草甸的影响。研究表明：（1）高原鼠兔与高原鼢鼠暴发活动形成的干扰斑块周长与面积比（PARA）、形状指数（SHAPE）和分形维数（FRAC）差异显著（P<0.05），其中高原鼢鼠斑块的FRAC是1.0124±0.0091，属于普通的规则几何圆形分布格局，高原鼠兔斑块的FRAC是1.1203±0.0546，属于分形几何不规则的分布格局。（2）高原鼠兔洞口数量与其斑块面积没有线性相关关系（P=0.9677），高原鼢鼠土丘数量与其斑块面积呈显著正相关（P<0.05）。（3）高原鼢鼠斑块面积统计学上呈长尾分布，不符合正态分布（P<0.01）。根据高原鼠兔斑块面积分布格局可将斑块演替分为三个阶段：土丘形成阶段、斑块连通阶段和斑块扩散阶段。高原鼠兔土丘形成阶段斑块的形状和分布，与高原鼢鼠干扰斑块相似；在演替初期阶段融合连通阶段斑块的面积分布呈指数分布，形状趋于分形几何（FRAC=1.1161）；在跨尺度扩散阶段斑块面积较大且形状复杂（SHAPE=4.4202），呈现不规则分布格局。三个阶段斑块的周长与面积比、形状指数和分形维数差异显著（P<0.05）。高原鼠兔在退化高寒草甸的觅食活动促进了融合连通阶段斑块的形成，呈现分形几何斑块演替规律。由此得出结论，引起高寒草甸退化的主要原因是过度放牧下高原鼠兔暴发活动，造成跨尺度扩散斑块演替阶段出现的结果，并非高原鼢鼠的暴发活动形成的。因此，控制高原鼠兔数量并恢复高原鼠兔干扰斑块植被相比高原鼢鼠更重要。 Abstract:Plateau pika (Ochotona curzoniae) and plateau zokor (Myospalax baileyi) are two species of small mammal widely distributed in alpine meadow. The main difference between the two animals is that plateau zokor mainly lives underground and plateau pika mainly lives on the surface of grassland. Their outbreak activities may cause serious degradation of alpine meadow. The disturbance patches formed by the two animals have different effects on the alpine meadow. Which kind of animal outbreak can lead to the cross-scale succession of disturbance patches is a scientific problem that needs to be solved. The patch shape and pattern metric in the field of landscape ecology can be used to compare the patch distribution patterns, thereby understanding the differences in the formation process of various patches. In this study, Unmanned aerial vehicle (UAVs) were used to capture typical images of plateau pika and plateau zokor population outbreak areas. Plateau pika holes, plateau zokor mounds and their disturbance patches were interpreted. The perimeter and area information of the disturbance patch was obtained. The shape and pattern metrics of disturbance patch were calculated and analyzed. The effects of outbreak activities of plateau pika and plateau zokor on the degradation of alpine meadow were determined. The results indicated that (1) there were significant differences in perimeter-area ratio (PARA), shape index (SHAPE) and fractal dimension index (FRAC) between plateau pika and plateau zokor disturbance patches formed by their outbreak activities (P<0.05). The FRAC of plateau zokor patches was 1.0132±0.0103, which belongs to ordinary regular geometry (circle), and the FRAC of plateau pika patches was 1.1007±0.0576, which belongs to fractal geometry. (2) There was no correlation between the number of plateau pika holes and the patch area of plateau pika (P=0.9677). There was a significantly positive correlation between the number of mounds and the patch area of plateau zokor (P<0.05). (3) The area of plateau zokor patch showed a long tail distribution at statistics, which did not accord with the normal distribution (P<0.01). According to the patch distribution pattern of plateau pika, the succession of patches could be divided into three stages:mound stage, fusion stage and broad-scale stage. The shape and distribution pattern of patches at the mound stage were similar to those of plateau zokor patches. At the fusion stage, the patch distribution was exponential, and the shape and pattern belonged to fractal geometry (FRAC=1.1161). At the broad-scale stage, the patch pattern was large and the shape was complex (SHAPE=4.4202). The patches at the broad-scale stage were formed by the connection between the surrounding fusion stage patches and the core area of black soil degraded patches, which destroyed the dynamic balance between disturbance and restoration of alpine meadow. There were significant differences among PARA, SHAPE and FRAC at the three stages (P<0.05). The foraging activities of plateau pika in the degradation of alpine meadow promoted the formation of patches and formed fractal geometric patches at the fusion stage. The main cross-scale interaction resulting in the degradation of alpine meadow was caused by the outbreak of plateau pika, not plateau zokor. Therefore, it is more important to control the number of plateau pika and restore the disturbance patches of plateau pika than those of plateau zokor. 参考文献 相似文献 引证文献

Major Type of Mattic-Epipedon Ruptures in Alpine Meadow Ecosystems on the Qinghai–Tibet Plateau

Alpine meadow degradation is an important issue for ecosystem stability in the Qinghai–Tibet Plateau (QTP). As an essential part of alpine meadow ecosystems, mattic epipedon (ME) refers to the soil surface horizons rich in organic matter and roots, which plays an important role in nutrient cycling, water retention, and ecological stability of QTP. The rupture of ME has caused serious alpine meadow degradation, biodiversity accidents, and ecosystem service decline, as well as attracted substantial concerns. However, the type of ME ruptures and their distribution environment are not well studied. In this perspective, to identify the major type of ME ruptures in QTP, 257 areas were investigated and 24 dominant plant species were collected from 2019 to 2023. Results indicated that ME ruptures exist in 234 investigated areas and can be broadly divided into 5 types based on visual observations and expert knowledge: collapsed ruptures, polygon ruptures, sheddable ruptures, cavernous ruptures, and hummock ruptures. The dominant plant species and coverage also present great differences between different rupture types. This study provides insights into alpine meadow degradation from the ME rupture types and distribution perspectives. Identifying the ME rupture types and their distribution will contribute to enhance alpine meadow restoration success for protecting the ecological benefits.

Pika disturbance intensity observation system via multidimensional stereoscopic surveying for monitoring alpine meadow

Plateau pika (Ochotona curzoniae) is a key species of alpine meadow ecosystem in Qinghai–Tibet Plateau. In this study, an observation and classification system of plateau pika disturbance intensity was constructed by multidimensional stereoscopic surveying, visual interpretation, geostatistics, principal component analysis, and clustering analysis, which can monitor and evaluate the disturbance of plateau pika activities comprehensively, scientifically, and efficiently in the head-water region of the Yellow River. The results show that (1) digital elevation model, digital orthophoto model, and three-dimensional real scene model can extract the surface morphology information changed by pika activities such as the number of pika holes and molehills, the area and volume of molehills, the elevation variation coefficient, the surface relief, and roughness; (2) The main load factors of the plateau pika disturbance intensity index (PPDII) are the surface roughness, the area and number of the molehills, and the number of mousehole; (3) The kappa value of PPDII clustering verification was 0.866, and the clustering analysis results were consistent with reality characteristics of plateau pika activity and distribution; (4) The disturbance in Laji Mountain is mainly slight and mild, accounting for 47.6% of sampling area, and the disturbance in Henan County is mainly medium and severe, accounting for 42.6% of sampling area. The results can provide reference data for the restoration and management of alpine meadow degradation in the head-water region of the Yellow River.

Degradation-driven bacterial homogenization closely associated with the loss of soil multifunctionality in alpine meadows

Alpine meadows are sensitive to climate change due to their unique ecosystem. The mechanisms by which soil microbial diversity regulates soil multifunctionality under degradation need to be extensively explored. In this study, three degraded levels of alpine meadows (nondegraded, ND; moderately degraded, MD; and severely degraded, SD) were chosen in the hinterland of Sanjiangyuan National Park on the Qinghai–Tibet Plateau. Soil microbial abundance and community structure were determined through 16 S rRNA, and six soil variables related to nutrient pools (DNA concentration, CDNA; soil organic matter, SOM; total N, TN; total P, TP; hydrolytic N, HN; and available P, AP) were measured and calculated for soil multifunctionality. The results showed that meadow degradation resulted in a decline in bacterial functional diversity and an increase in compositional diversity (Shannon index and richness). Soil fungi were less sensitive to meadow degradation. Meanwhile, soil individual functions, such as SOM, TN, HN, AP, and multifunctionality, decreased significantly when subjected to meadow degradation. Moreover, bacterial functional diversity and the Shannon index, rather than bacterial richness, had significantly positive and negative relationships with soil multifunctionality, respectively. Furthermore, the dissimilarity of bacterial communities decreased with degradation. These results indicated that meadow degradation led to bacterial homogenization and functional redundancy, all of which would reduce soil multifunctionality. Abiotic factors such as soil water content (SWC) and bulk density (BD) also significantly changed and still played a key role in regulating the soil multifunctionality accompanying degradation. Amino-acid metabolism had the highest relative abundance (4.37%) and was negatively correlated with SOM and TN, implying that bacteria may convert more limited resources for their own needs and increase the loss of soil multifunctionality under severe degradation. The results provide new insight into the relationships between biodiversity and ecosystem multifunctionality and scientific guidance for the restoration of degraded alpine meadows.

Progress on evaluation of Alpine grassland degradation degree in Qinghai Province

The alpine grassland in Qinghai Province is very prone to degradation, and the local ecosystem is fragile. If damaged, it is difficult to recover in a short time. Because of alpine grassland degradation phenomenon will directly threaten the local ecological security and economic development, so the current research scholars strengthen the assessment of the degree of degraded alpine meadow, pay attention to the alpine grassland degradation phenomenon from the perspective of practice to master the spatial distribution law of deep excavation latent information value, in order to provide evidence for effective protection measures. On the basis of understanding the current alpine grassland degradation phenomenon in Qinghai Province, this paper systematically collected local basic geographic, social economic, scientific investigation and other data information, combined with the basic law of alpine grassland degradation, and used geographic information technology and statistical methods to determine the evaluation results of alpine grassland degradation degree in Qinghai Province. The final results showed that although the degradation of the local alpine grassland was still severe, with the improvement of the attention of various departments, the grassland protection work had achieved excellent results.

Effect of Nitrogen Addition on Soil Fungal Diversity in a Degraded Alpine Meadow at Different Slopes

This study proposed nitrogen addition experiments to analyze the effects of exogenous nitrogen addition on soil fungal diversity in alpine meadow. All the experiments were performed in degraded alpine meadow with two different slopes (gentle slope and steep slope) in Guoluo Prefecture of the Sanjiangyuan Region, and the sequence and analysis of ITS of soil fungi were performed using MiSeq PE250 sequencing technology. Comparative analysis was carried out with three nitrogen addition levels on soil fungal diversity in degraded grassland with different slopes, which included low nitrogen (LN, 2 g·m-2), middle nitrogen (MN, 5 g·m-2), and high nitrogen (HN, 10 g·m-2). The results showed that:① the distribution groups of fungi in the soil were Ascomycota, Basidiomycota, Mortierellomycota, and Glomomycota, and the dominant bacteria was Ascomycota. ② The dominant genera were Mortierella and Archaeorhizomyces, and there were no differences in response to different slopes and nitrogen addition levels. ③ A total of 95 genera (Gibberellum, Preussia, etc.) were identified and significantly differed between two different slopes (P<0.05). ④ Bacteria with a relative abundance less than 1% had significant differences in nitrogen addition at different levels on the same slope (P<0.05). 5 In addition, the analyses of α and β diversities showed that soil fungal community structure was stable under different slopes and nitrogen addition levels. Exogenous nitrogen supplementation significantly improved the relative abundance of non-dominant fungal communities without destroying soil fungal community structure.

Plasticity in over-compensatory growth along an alpine meadow degradation gradient on the Qinghai-Tibetan Plateau

Over-compensatory growth of plants after disturbance is generally preferred by grassland users and managers because of more forage. How the grassland productivity and the plant growth condition before disturbance affect the compensatory growth are important for grazing management and the understanding of grassland degradation, yet they are not well understood. A clipping experiment was conducted on the Qinghai-Tibetan Plateau to understand the compensatory growth and conditions for the occurrence of over-compensatory at alpine meadows with different degradation status. Results showed the competition for light constrains the plant growth post-clipping at non-degraded and slightly degraded alpine meadows, while the reduction of soil nitrogen limits it at heavily degraded alpine meadow. The biomass accumulated post-clipping was positively correlated with the growing season biomass in unclipped plots and the biomass at clipping in clipped plots. When the aboveground biomass at clipping was less than 40.10 g m−2 and the growing season biomass was between 38 and 97 g m−2, the over-compensatory growth of alpine meadow could occur. Higher clipping rate is required for the alpine meadow with high productivity but the maximum clipping rate should be less than 0.71 to induce the over-compensatory growth. Equal-compensatory occurred at non-degraded and slightly degraded, while over-compensatory growth was observed at moderately degraded and a marginally significant over-compensatory growth at heavily degraded alpine meadow. The over-compensatory growth occurred at moderately degraded alpine meadow is mainly due to the performance of forbs. Our results suggest that grazing at moderately degraded alpine meadow may induce the over-compensatory growth at the community level, but the over-compensatory growth of forbs at moderately degraded alpine meadow may aggravate the alpine meadow degradation.

Analysis on the soil physical, chemical, and microbial community properties of different alpine meadow patches in the Source Zone of the Yellow River, West China

Severe degradation of alpine meadow in the Source Zone of the Yellow River (SZYR) seriously affects the stability and sustainability of the local grassland ecosystem. Although some progress has been made in understanding the degradation process, mechanism and restoration, existing restoration technologies do not target at topographic and hydrothermal conditions, resulting in instability and poor sustainability of the restored ecosystem. This study quantified the effects of grassland degradation severity (non-degraded patch (NP), vegetated patch (VP), bare patch (BP)) on the soil physical, chemical properties and microbial community composition and their interactions in the alpine meadow in the SZYR on the Eastern Qinghai-Tibet Plateau, West China. Results showed that as the degradation severity worsens from NP to BP, soil moisture, total porosity, electrical conductivity, and root biomass decreased significantly, while soil bulk density and permeability increased significantly. The contents of soil organic carbon, total nitrogen and total phosphorus decreased significantly with the enlargement of meadow patches. There were significant differences in community structure and functional microorganisms of soil bacteria and fungi in different meadow patches. In conclusion, strategies such as replanting local grass species, adding organic fertilizer and microbial fertilizers and increasing soil compaction intensity of patches to maintain soil moisture, should be considered for restoring the degraded meadow patches.

Grazing rest during spring regreening period promotes the ecological restoration of degraded alpine meadow vegetation through enhanced plant photosynthesis and respiration.

Grazing rest during the spring regreening period is the most economical and feasible measure for the ecological restoration of degraded alpine meadows and has been widely popularized and applied in China. The aim of the present study was to undertake a comparative analysis of the effects of grazing rest on the ecological restoration of degraded alpine meadows by plant photosynthesis and respiration. Coverage, height, ground biomass, belowground biomass of degraded alpine meadow vegetation, net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO2 concentration, chlorophyll fluorescence parameters, relative chlorophyll content, respiration rate, metabolite content, leaf relative water content, and related mineral element content of the dominant grass Elymus nutans Griseb. were measured in degraded alpine grassland with different grazing rest years. The results show that grazing rest during the spring regreening period promoted the ecological restoration of degraded alpine meadows by enhancing the photosynthesis and respiration of the dominant grass E. nutans Griseb. Grazing rest enhanced photosynthesis in dominant grass by increasing metabolites related to the Calvin cycle, chlorophyll content, leaf relative water content, and related mineral element content. Grazing at rest enhanced the respiration of dominant grass by increasing metabolites related to the TCA cycle, leaf relative water content, and related mineral element content. This positive effect gradually became stable with increasing years of grazing rest. Our results provide a fundamental basis for the popularization and application of grazing rest during the spring regreening period on degraded Tibetan Plateau grasslands.

Effects of establishing cultivated grassland on soil organic carbon fractions in a degraded alpine meadow on the Tibetan Plateau.

BackgroundThe degradation of alpine meadows has induced substantial losses of soil organic carbon (SOC) on the Tibetan Plateau. A commonly-used method for rehabilitating degraded alpine meadows in this region is establishing cultivated grasslands through sowing seed mixtures, but its impact on the biochemical stability of SOC has remained inadequately explored.MethodsIn this study, a total of 20 composited 0-20 cm soil samples were collected from a heavily degraded alpine meadow (DM) and three adjacent cultivated grasslands established for 3 years (CG3), 12 years (CG12), and 17 years (CG17) on the eastern Tibetan Plateau, and the SOC pool was separated into labile C pool I (LOC I), labile C pool II (LOC II), and recalcitrant C pool (ROC) in order to investigate changes in contents of SOC fractions that have different biochemical stabilities after the establishment of cultivated grassland.ResultsAlthough the establishment of cultivated grasslands led to increases in soil total organic C content, the increase was only significant in samples with 17 years of cultivation. We found that the contents of the three SOC fractions were higher at CG3 and CG12 compared with those in the DM, and the differences were only significant for soil LOC II. By comparison, 17 years of cultivation led to significant increases in all of the SOC fraction contents. The results implied that different cultivation years had distinct impacts on SOC fractions in cultivated grasslands, and longer cultivation years contributed to accumulated soil ROC. The recalcitrance index of SOC in the DM was higher than that at CG3 and CG12, but lower than that at CG17. This was possibly due to the generally low litter quality of cultivated grasslands, which led to a slow release of complex compounds to soils. Moreover, it was observed that soil C:N ratio was a potential indicator of SOC biochemical stability because of their close correlation.ConclusionsOur findings suggest that the long-term establishment of cultivated grasslands on DM is a promising solution to recovering both the quantity and stability of SOC on the Tibetan Plateau.

Changes in Soil Bacterial Community Diversity in Degraded Patches of Alpine Meadow in the Source Area of the Yellow River

MiSeq sequencing technology was used to investigate the bacterial compositions and diversities of active patch, non-active patch, recovered patch, and healthy alpine meadows so as to understand the changes in soil bacterial community diversity during altitude change and alpine meadow degradation. The relationship between bacterial diversity and environmental factors was analyzed using redundancy analysis (RDA). The results showed that the dominant bacterial phyla in the soil included Proteobacteria, Actinobacteriota, and Acidobacteriota in the study areas. The dominant bacterial genera that were identified via the MiSeq were RB41, Sphingomonas, and Bradyrhizobium. The relative abundance of these genera decreased with altitude increase and increased with the restoration progress of degraded patches but was significantly lower than that in the alpine meadow (P<0.05). The abundance of functional bacteria related to carbon fixation in degraded patches was higher than that in the healthy alpine meadow. The bacterial Chao1 index and species number in different types of degraded patches were significantly higher than those in the alpine meadow (P<0.05). The results of the RDA suggest that biological soil crust coverage and total nitrogen were the main influencing factors on dominant bacterial phyla at the altitude of 4013 m. Biomass, total nitrogen, and pH had a great influence on the dominant bacterial phyla at the altitude of 4224 m. Biomass and total potassium significantly affected the distribution of bacterial genera at the altitude of 4013 m. Sedge coverage and available nitrogen were the main influencing factors on bacterial dominant genera at the altitude of 4224 m. Biological soil crusts and pH had a great influence on bacterial diversities. The bacterial influence factors varied greatly at different altitude areas. Therefore, we should not only pay attention to the effect of alpine meadow degradation but also consider the effect of altitude in the study of bacterial diversity changes.

Animal Activities of the Key Herbivore Plateau Pika (Ochotona curzoniae) on the Qinghai-Tibetan Plateau Affect Grassland Microbial Networks and Ecosystem Functions.

Plateau pikas (Ochotona curzoniae) are high-altitude model animals and famous “ecosystem engineers” on the Qinghai-Tibet Plateau. Pika activities may accelerate the degradation of alpine meadows. Nevertheless, little is known about the responses of bacterial, fungal, and archaeal communities, and ecosystem multifunctionality to pika perturbations. To address this question, we studied the impacts of only pika disturbance and combined disturbance (pika disturbance and grazing) on ecological networks of soil microbial communities and ecosystem multifunctionality. Our results demonstrated that Proteobacteria, Ascomycota, and Crenarchaeota were dominant in bacteria, fungi, and archaea, respectively. Bacteria, fungi, and archaea were all influenced by the combined disturbance of grazing and pika. Most fungal communities became convergent, while bacterial and archaeal communities became differentiated during the succession of surface types. In particular, the bacterial and fungal networks were less stable than archaeal networks. In response to the interference, cross-domain cooperation between bacterial and fungal communities increased, while competitive interactions between bacterial and archaeal communities increased. Pika disturbance at high intensity significantly reduced the ecosystem multifunctionality. However, the mixed effects of grazing and pika weakened such influences. This study revealed how pika activities affected microbial networks and ecosystem multifunctionality. These results provide insights to designing reasonable ecological management strategies for alpine grassland ecosystems.

Effects of Nitrogen Addition on Soil Carbon-Fixing Microbial Diversity on Different Slopes in a Degraded Alpine Meadow.

Autotrophic carbon-fixing bacteria are a major driver of carbon sequestration and elemental cycling in grassland ecosystems. The characteristics of the response of carbon-fixing bacterial communities to nitrogen (N) addition in degraded alpine meadows are unclear. In this study, it was investigated that the effects of N addition in three levels [they are low (LN), middle (MN), and high (HN) with N supplement of 2, 5, and 10 g N⋅m–2⋅a–1, respectively] on soil carbon-fixing bacteria on different slopes in a degraded alpine meadow in the Yellow River on the Qinghai–Tibet Plateau. The results showed that there were significant differences in the abundance of some low abundance genera of carbon-fixing bacteria on the same slope (P < 0.05), but the differences in the abundance of various phyla and dominant genera were not significant. MN on gentle slopes significantly reduced the Chao1 index and observed species (P < 0.05), whereas N addition on steep slopes had no significant effect on the diversity. The abundance of the Cyanobacteria phylum and 28 genera of identified carbon-fixing bacteria differed significantly between slopes (P < 0.05), and observed species of carbon-fixing bacteria were significantly higher on steep slopes than on gentle slopes (P < 0.05). Factors affecting the carbon-fixing bacteria community structure include slope, N addition, ammoniacal nitrogen (N-NH4+), microbial biomass carbon (MBC), soil water content (SWC), pH, soil C:N ratio, and microbial C:N ratio. Slope, N addition, soil physicochemical properties, microbial biomass, and stoichiometric ratio did not significantly affect the carbon-fixing bacteria diversity. Thus, the effect of exogenous N addition on carbon-fixing bacteria in degraded alpine meadows was dependent on slope conditions, and the response of carbon-fixing bacteria abundance and species number to N addition on gently slope sites was threshold-limited.

Effects of regulation measure on soil and microbial biomass of moderately degraded alpine meadow in Qilian Mountain, China

We examined the effects of different regulation measures (spring rest grazing, spring rest grazing-cutting turf, spring rest grazing-cutting turf-fertilization, spring rest grazing-cutting turf-sowing, spring rest grazing-cutting turf-fertilization-sowing) on vegetation, soil physical and chemical properties, and soil microbial biomass in mode-rately degraded alpine meadow in Qilian Mountain. The results showed that all the regulation measures significantly increased plant coverage and aboveground and underground biomass of degraded alpine meadows. Plant species richness increased significantly under the two measures of spring rest grazing-cutting turf-fertilization and spring rest grazing-cutting turf-fertilization-sowing. The dominant species of spring rest grazing-cutting turf-sowing and spring rest grazing-cutting turf-fertilization-sowing was Poa pratensis cv. Qinghai. Soil pH and bulk density in moderately degraded alpine meadow (control) were significantly higher than those of all regulation measures. Soil water content, soil organic carbon, total nitrogen and total potassium, carbon-nitrogen ratio and nitrogen-phosphorus ratio of spring rest grazing-cutting turf-fertilization-sowing measures were the highest, which were 21.3%, 22.30 g·kg-1, 2.77 g·kg-1, 19.93 g·kg-1, 8.3 and 3.5, respectively. Soil microbial biomass nitrogen and phosphorus (104.98 and 40.74 mg·kg-1) of degraded meadows under spring rest grazing-cutting turf-fertilization-sowing measures were significantly higher than those of other measures, while soil microbial biomass carbon (240.72 mg·kg-1) of degraded meadows under spring rest grazing-cutting turf-fertilization measures was significantly higher than that of other measures. The results of radar map showed that the regulation measures affected the characteristics of degra-ded meadow vegetation (aboveground and underground biomass), soil physical and chemical properties (water content, organic carbon, total nitrogen, total phosphorus, and total potassium) and soil microbial biomass (carbon, nitrogen and phosphorus). Spring rest grazing-cutting turf-fertilization-sowing measures had the best performance in restoraing degraded meadows in the study area.

The Plant Interspecific Association in the Revegetated Alpine Grasslands Determines the Productivity Stability of Plant Community Across Restoration Time on Qinghai-Tibetan Plateau.

Grassland cultivation is the key measure for restoring “Black Beach,” the extremely degraded alpine meadow in the Three River Headwater Area of the Qinghai–Tibetan Plateau. In this study, we examined the inter-specific relationship in the vegetation community of cultivated grasslands with different restoration times through the network analysis method. The results showed that with the extension of restoration time, the development of cultivated grassland would lead to increasing neutral interactions among the plant species. The proportion of species with positive and negative associations in the community decreased, while the number of species-independent pairs increased significantly. The complexity of plant interspecific association (species network density) had more influence on community stability with the extension of recovery time, which can be used to quantify the characteristics of community structure.

Ecosystem Coupling and Ecosystem Multifunctionality May Evaluate the Plant Succession Induced by Grazing in Alpine Meadow.

Most alpine meadow on the Tibetan Plateau are at different stages of community succession induced by grazing practices. Quantifying the succession sequence and assessing the dynamics of plant composition, ecosystem coupling, and multifunctionality across successional stages are essential for reasonable restoration of degraded alpine meadow. Here, we selected areas with different grazing disturbance histories and used them as a space series (i.e., space-for-time substitution) to study the community succession. Our work quantified the plant succession sequence of alpine meadow induced by grazing with plant functional group approach. The plant succession sequence is from the tall sedge community with erect growth to the short undesirable toxic forbs community with prostrate growth. Ecosystem coupling, ecosystem multifunctionality and their relationships were all the lowest in Stage 4. Compared to Stage 4, the ecosystem multifunctionality index increased in Stages 1, 2, and 3 by 102.6, 89.8, and 207.6%, respectively; the extent of ecosystem coupling increased by 20.0, 16.8, and 21.2%, respectively. Our results indicated that the driving factors of ecosystem coupling and ecosystem multifunctionality were soil factor individual in early successional stage to plant-soil simultaneously in late successional stage. Our results also highlighted the importance of toxic weeds during the late stage of degraded succession and suggest that the expansion of toxic plants is a consequence of their greater suitability from a successional perspective. The findings of this study would provide valuable guidance for optimizing the management and restoration practice of alpine meadow.

Effect ofElymus nutans on the assemblage of arbuscular mycorrhizal fungal communities enhanced by soil available nitrogen in the restoration succession of revegetated grassland on theQinghai‐TibetanPlateau

AbstractThe succession of arbuscular mycorrhizal fungi (AMF) communities during ecosystem development has received widespread attention, but the ecological mechanism that drives the succession of AMF communities during the restoration process in alpine meadow ecosystems remains unclear. Here, we treated ‘Black Beach’ (severely degraded alpine meadow) as the baseline for restoration (0 year), and selected the revegetated grassland ofElymus nutanswith different planting times (3, 7, 10, and 14 years) to analyze the species composition of the AMF community in mixed roots (at the whole‐plant‐community scale) and inE. nutansroots (at the single‐plant‐species scale). A total of 46 AMF phylotypes (mixed roots: 44;E. nutansroots: 46) were identified in both root systems, predominantly belonging to Glomeraceae. AMF species richness showed a single‐peak curve change across the restoration time and reached its peak at 3 years in both root systems. In mixed roots, the soil available nitrogen not only directly changed the AMF species composition but also indirectly changed the AMF species composition through plant richness. In theE. nutansroots, only the soil available nitrogen drove changes in AMF species composition through changes in plant richness. Our results indicate thatE. nutans, a key species in the restoration process of revegetated grassland, can enhance its regulation to assemble the AMF community through soil available nitrogen at the two research scales, suggesting that the scientific management of soil nitrogen availability during restoration succession could strengthen the mutual symbiosis of ‘plant‐AMF,’ thereby retarding the occurrence of secondary degradation of revegetated grassland.

Land Degradation Changes the Role of Above- and Belowground Competition in Regulating Plant Biomass Allocation in an Alpine Meadow.

The allocation pattern of plant biomass presents the strategy of the plant community to adopt environmental changes, while the driver of biomass allocation is still unclear in degraded alpine grassland ecosystems. To explore the issue, this study investigated the shoot-to-root (R/S) ratio, plant aboveground traits, and root competition of three functional groups (i.e., grasses, sedges, and forbs) at three degradation levels (i.e., no obvious degradation, ND; moderate degradation, MD; and severe degradation, SD) in an alpine meadow in the eastern Qinghai-Tibetan Plateau. The relationships among plant aboveground traits, root competition, and R/S ratio were tested using the structural equation model (SEM). The results showed that the shoot and root biomass tended to decrease, but the R/S ratio of the plant community did not change along the degradation gradient. Plant height, lateral spread, and leaf length of most plant functional groups reduced, while leaf width and leaf area of most plant functional groups did not change along the degradation gradients. The root competition ability (presented as the fraction of root biomass in total biomass) of sedges in MD was the lowest, while that of grasses was the highest. The effects of aboveground competition on the R/S ratio were non-linear because of the different roles of plant height, lateral spread, and leaf area in regulating the R/S ratio along the degradation gradient. In contrast, the effects of belowground competition on the R/S ratio were linear because belowground competition promoted the R/S ratio, and the strength of this effect reduced along the degradation gradient. These results indicate that plant competition might be a critical factor to maintain the high R/S ratio in degraded alpine meadows.