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Soil organic carbon (SOC) is an important component of the global carbon pool, whose accumulation and decomposition affect the balance of the global carbon cycle and climate change. However, understanding of the responses of SOC in alpine ecosystems to climate change is quite limited, especially in the seasonal-frozen soil zone. In order to understand the impact of soil moisture changes on the carbon cycle in alpine mountain ecosystems, we established two sample plots of the semi-shady and semi-sunny slopes in the subalpine meadow zone of the eastern part of Qilian Mountains, and collected soil samples to investigate the spatial and temporal changes of SOC and soil moisture and their relationships. The study indicated that the SOC content showed significant surface aggregation during the plant growing season, and that the influence of soil moisture on SOC was different in different slope directions and soil depths. The influence of soil moisture on SOC was greater on the semi-shady slope than on the semi-sunny slope. Among different soil layer depths, the soil moisture most significantly affected SOC in the soil layer of 20-40 cm. This study provides a theoretical basis for the study of carbon stocks and carbon cycling at high altitudes. [ABSTRACT FROM AUTHOR]

The species number of bryophytes is the second highest among land plants. Alpine grasslands on the Qinghai–Tibet Plateau (QTP) are the largest among global alpine biomes. However, bryophyte flora in alpine grasslands on the QTP remains poorly explored relative to its large geographic extent. A total of 347 plots were surveyed across the QTP, and 149 bryophyte taxa in 24 families and 49 genera were recorded in alpine grasslands. The largest family was Pottiaceae, followed by Bryaceae and Brachytheciaceae. The most species-rich genus was Bryum, followed by Didymodon and Brachythecium. The dominant species were Didymodon tectorus, Didymodon fallax, Bryum caespiticium, Didymodon constrictus, and Didymodon ditrichoides. The Jaccard similarity indexes of bryophyte compositions between alpine meadow and alpine steppe at the family, genus, and species levels were 0.375, 0.367, and 0.282, respectively. Turf was the most common life-form (75.2%), followed by weft (16.1%) and cushion (5.4%). Endemic species to China accounted for 8.05% of the total taxa. Bryophyte diversity in alpine grasslands on the QTP is exceptional and irreplaceable. The changes in species composition and life-forms between different grassland types reflect the adaptations of bryophytes to harsh environments. [ABSTRACT FROM AUTHOR]

Nitrogen is the crucially sustainable element for most ecosystem including grassland. Fenced alpine meadow grassland (FG), lightly, moderately and heavily degraded (LD, MD and HD) alpine meadow in spring, summer and winter were studied to clear the effects of alpine meadow degradation on soil total nitrogen (TN), available nitrogen (AN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3–-N), inorganic nitrogen (IN) content and the ratio of inorganic nitrogen to available nitrogen (IN/AN), and to find practical management strategies on the background of alpine meadow degradation and ecological environment restoration in the Eastern Qilian Mountains area, northwest China. The results showed that soil total nitrogen contents of the alpine meadow types were at a low level, ranged from 1.60 g·kg−1 to 5.15 g·kg−1, but soil available nitrogen contents was at a high level, ranged from 373.2 mg·kg−1 to 650.8 mg·kg−1in the study area. Alpine meadow degradation can seasonally change soil nitrogen status. Degraded alpine meadow had more inorganic nitrogen than fenced meadow in surface soil. Degradation only changed soil NO3−-N profile distribution in winter and had no significant effect on profile distribution of TN, AN, NH4+-N and IN. There were significant interactions of alpine meadow types, seasons and soil depth on soil available nitrogen, NH4+-N, NO3–-N and inorganic nitrogen content. Although soil available nitrogen increased under degradation, nitrogen input is needed in the restoration of heavily degraded alpine meadow during the summer growing season to improve vegetation coverage because of the low soil inorganic nitrogen and IN/AN ratio in summer growing season in 10–20 cm and 20–30 cm depth. [ABSTRACT FROM AUTHOR]

Question: Patchiness of herbaceous species is a common feature of degraded alpine grasslands on the Qinghai–Tibet Plateau; however, the impact of this phenomenon on vegetation, soil seed bank (SSB), and soil carbon (C) and nitrogen (N) is largely unknown. We asked how different herbaceous patches affect above‐ground vegetation, the SSB and soil organic C (SOC) and total N (TN) contents in alpine meadows. Location: An alpine meadow on the Qinghai–Tibetan Plateau, China. Methods: We used field and greenhouse experiments to evaluate above‐ground vegetation parameters, the SSB composition, and SOC and TN contents of four commonly distributed herbaceous patches (Leymus secalinus, Kobresia humilis, Leontopodium nanum and Pedicularis kansuensis) and non‐patch vegetation (control). Results: There were significant differences in the species composition of above‐ground vegetation, with the plant species richness, Shannon–Wiener index, Simpson index, and Pielou evenness index reduced in the four patches compared to the control. In addition, patches had increased above‐ground biomass (AGB) and a lower below‐ground biomass to above‐ground biomass ratio (BGB:AGB); while the species diversity indices did not change considerably among the patches. The species composition of the SSB in the four patches differed from that in the control and the seed density increased markedly, but the species richness and diversity of the SSB remained unaltered. Moreover, the contents of SOC, total C, TN, microbial biomass C, and microbial biomass N in the four patches were markedly lower than in the control. Conclusions: These findings suggest that patchiness of herbaceous species can alter the flora composition of alpine meadows and reduce plant species diversity, as well as the SOC and TN contents, which will adversely impact grassland biodiversity conservation and soil C sequestration, and then may intensify the degradation of alpine meadows on the Qinghai–Tibet Plateau. [ABSTRACT FROM AUTHOR]

The relationship between biodiversity and ecosystem multifunctionality (EMF) is critical to understanding the dynamics of ecosystem services. Several studies have investigated alterations in multiple ecosystem functions under grassland degradation and its relationship with taxonomic diversity. However, how multidimensional biodiversity (taxonomic, functional, and phylogenetic diversity) and abiotic factors mediate EMF in degraded alpine meadows has yet to be well been explored. In this study, alpine meadows with different degrees of degradation were investigated in Maqu County, Gansu Province, China. The average and multi‐threshold methods were used to quantify EMF, while structural equation modeling (SEM) was used for statistical analysis. The results show that: (1) Degradation of alpine meadows has altered the species composition and diversity of plant communities. (2) Taxonomic, functional, and phylogenetic diversity were all significantly and positively correlated with EMF, and species richness, functional richness and Faith's PD effectively drive EMF within thresholds of 22%–75%, 20%–86% and 42%–72%, with maximum effects of 0.29, 0.33 and 0.12, respectively. (3) Degradation of alpine meadows directly and significantly reduced EMF, and mediated indirectly through plant diversity and soil abiotic factors. The multifunctionality index for different degrees of degradation showed non‐degraded (60.89) > light degraded (37.84) > moderate degraded (−14.17) > heavy degraded (−48.55). The results of this study reveal the relative importance of multidimensional plant diversity in predicting EMF of degraded alpine meadows, and potential mechanisms by which plant diversity and abiotic factors mediate the effects of alpine meadow degradation on EMF. [ABSTRACT FROM AUTHOR]

Global grassland degradation has prompted professionals and practitioners to critically consider about the future of grassland resources. Restoration actions related to payment for ecosystem services (PES) have been proposed as a possible approach to balancing grassland sustainable development and ecosystem service supply. Since 2005, approximately one billion U.S. dollars have been invested in the Three-River Headwater Region (TRHR) of China to restore 5.69 × 106 ha of degraded grasslands via grassland cultivation and fencing. Unfortunately, few literature has drawn valid and generalizable conclusions regarding the economic performance of these PES programs. Therefore, field data from multiple sites were collected to evaluate the economic returns of restoration actions, returns on investments (ROI), and trade-offs among ecosystem services of cultivated and fenced grasslands over different restoration years in the TRHR. The results revealed that PES-related restoration efforts in the TRHR had yielded a net profit of $14.34 billion, with $13.20 billion from the alpine meadow, $0.74 billion from the alpine steppe and $0.40 billion from the temperate steppe. These substantial economic can be attributed to the combined effects of the surge in specific ecosystem services and the synergistic improvement of all ecosystem services. The ROI of supporting service accounted for the largest proportion of ROI in total ecosystem services and exhibited drastic fluctuations with restoration years, whereas the ROI of other services either increased gradually or remained stable across different restoration periods. The trade-offs in ecosystem services varied greatly with grassland type. We observed an increasing synchronization of ecosystem services over time in the fenced alpine steppe, cultivated alpine meadow, and cultivated temperate steppe; whereas a similar trend was not detected in other grasslands. Our research underscores the importance of incorporating herders' willingness, assessing restoration performance of grasslands and adopting more targeted and adaptive restoration actions in subsequent PES programs. • PES helped balance sustainable development and ecosystem conservation. • Multiple site data was collected to explore ecological returns of restoration actions. • Restoration actions with PES programs had yielded a net profit of $14.34 billion. • Gains were owed to surge of specific ecosystem services and synergy of all services. • Herders' willingness and more targeted actions should be considered in next steps. [ABSTRACT FROM AUTHOR]

• Soil erosion rate was 3 times greater on the south-facing hillslope as compared to the north-facing hillslope. • Soil water content was the dominant factor causing the difference in erosion rates under a water-limited condition. • Greater soil erosion rates resulted in elevational distributions of soil physicochemical properties on the south-facing hillslope. Soil erosion causes serious grassland degradation in the Three-River Headwater Region (TRHR) of the Qinghai-Tibet Plateau. Identifying source areas of erosion is important, including understanding the influences of hillslope aspect on soil erosion. However, the effect of hillslope aspect on soil erosion is a much-debated process, wherein contrasting results were previously reported. We hypothesized that aspect-induced differences in environmental variables will be related to differences in erosion magnitude and spatial pattern, and that these differences will impact soil physiochemical characteristics as well. To test this hypothesis, soil samples were collected at conjoined south- and north-facing hillslopes along elevational profiles in a small watershed in Yushu County, with measurements of soil water content (SWC), soil organic carbon (SOC), soil organic matter (SOM), soil particle size distribution, soil total nitrogen (STN) and phosphorus (STP). Soil erosion rate was estimated using 137Cs technology. The results showed that soil erosion rates of the two hillslopes ranged from 0.073 to 10.83 t ha-1 yr-1, and were 3 times greater on the south-facing hillslope. Soil water content ranged from 7.6% to 76.8% on the two hillslopes with lower values on the south-facing hillslope due to the greater solar radiation. By Spearman correlation analysis and path analysis, we concluded that lower soil water content on the south-facing hillslope restricts vegetation growth, and hence resulting in greater soil erosion under the case where vegetation growth is dominantly controlled by water availability. Greater soil erosion on the south-facing hillslope caused greater surficial accumulation of coarser materials and greater loss of soil nutrients, which are expected to complicate the hydrological erosion process. Moreover, the downslope increased soil erosion rate should be fully considered in conservation practices. These results will improve our understanding of the interaction and feedback mechanisms between soil characteristics, vegetation function, and soil erosion in the TRHR. [ABSTRACT FROM AUTHOR]

• Patchiness caused significant reduction of SOC and TN stocks. • Reduced vegetation input and increased erosion output accounted for SOC and TN loss. • Grasslands with high patchiness had a great potential for C and N sequestration. Patchiness acts as an indicator of terrestrial ecosystem degradation and can lead to considerable loss of soil organic carbon and total nitrogen. However, quantitative assessments of the effects of patchiness on soil organic carbon and total nitrogen stocks and their associated mechanisms remain limited. This study aimed to explore the influence mechanisms of patchiness on soil organic carbon and total nitrogen stocks and to project the quantitative contribution of the further expansion of patchiness and vegetation recovery. Soil properties, soil organic carbon and total nitrogen stocks were investigated using a combination of field sampling and aerial photography in four grassland types, alpine meadow, alpine steppe, temperate grassland, and desert grassland, at 47 sites in northwestern China. Soil organic carbon and total nitrogen densities in the bare patches were 34–54 % and 23–41 % lower, respectively, compared to the original vegetation. At the plot-scale, current soil organic carbon and total nitrogen stocks ranged from 30.85 to 77.80 T/ha and 3.26 to 10.19 T/ha, respectively, across grassland types; with a 10–27 % and 7–24 % potential loss of soil organic carbon and total nitrogen stocks, respectively, from the further expansion of patchiness but a 10–50 % and 9–37 % potential increase in soil organic carbon and total nitrogen stocks, respectively, from vegetation recovery. Soil organic carbon and total nitrogen stocks were positively correlated with vegetation biomass, soil clay content, and precipitation (p < 0.001), whereas they were negatively correlated with patchiness (p < 0.001). In summary, patchiness reduced soil organic carbon and total nitrogen stocks by decreasing vegetation inputs and increasing erosion outputs, while vegetation recovery showed potential for increasing carbon and nitrogen stocks. Our results highlight that maintaining intact vegetation cover is critical for preserving terrestrial ecosystem carbon and nitrogen storage. [ABSTRACT FROM AUTHOR]

• Mineral-associated organic carbon and hot-water extractable carbon of the alpine meadow varied strongly across parent materials. • Soil geochemistry dominated the variation of SOC fractions in the alpine meadow. • Root functional traits exerted stronger control on SOC fractions in deeper soil. Alpine meadow occupies ～46.7 % of the grassland area and stores more than 60 % of the soil organic carbon (SOC) in the Qinghai-Tibet Plateau, with 3.19 Pg C in the top 30 cm. Parent material can highly influence SOC stocks via various mineral components with divergent adsorption abilities. However, previous studies mainly concentrated on the relation between SOC and parent material in temperate and tropical forest ecosystems, evidences from different environments are needed to gain a holistic understanding. In this study, we explored how the functional distinct SOC fractions (the particulate (POC), mineral-associated (MAOC), and hot-water extractable carbon (HWEOC)) vary among four types of parent materials (monzonitic granite (MG), slate (SL), muscovite schist (SH), and diorite (DI)) by measurements from 16 sites on the Qinghai-Tibet Plateau. We also assessed the plant and geochemical factors in controlling the divergent SOC fractions. We found that MAOC and HWEOC vary strongly, while POC remain stable among parent materials due to sufficient plant input and slow decompositions rate. Moreover, our results revealed that geochemical factors exert dominant controls on each SOC fraction, with soil pH and texture showing a significant influence. Soils developed from the SL displayed the highest MAOC and HWEOC compared with that formed on the other three parent materials due to finer soil texture as well as relative high multivalent Ca and Mg. Furthermore, root traits increased its control on SOC fractions in relatively deeper soil depth (10–30 cm). Taken together, these results provided evidence of the key role of parent material in controlling the divergent SOC fractions in the less weathered alpine regions, emphasizing that parent material and soil geochemistry should be adequately considered in the biogeochemical and Earth system models. [ABSTRACT FROM AUTHOR]

[Display omitted] • Divergent succession changed community structure with decreased Sedge and Leguminous. • Soil water holding capacity, carbon stocks functions decreased with divergent succession. • Succession to shrubs and forbs both decreased ecosystem multifunctionality of alpine meadow. Global climate change and overgrazing pressure both affects the community succession, and multifunctionality of grassland ecosystems. Alpine meadows cover 1/3 of the Qinghai-Tibetan Plateau of China's climate sensitive area and major pastures, which is the main grassland ecosystem. However, the responses of ecosystem multifunctionality during climate change and overgrazing induced divergent community succession to shrubs- and forbs-dominated community remains poorly understood in alpine meadow ecosystem. Here, we examined five ecological functions, including above- and below-ground productivity, soil water holding capacity, soil organic carbon stocks and soil erosion resistance capacity of the native Kobresia -dominated alpine meadow ecosystem during the divergent succession to shrubs- and forbs-dominated meadow located on the Qinghai-Tibetan Plateau, and identified the key factors contributing to the changes of ecosystem multifunctionality during the divergent succession. Results showed that the divergent succession to shrubs- and forbs-dominated meadow both significantly reduced community species diversity and richness, changed community structure, especially the decreasing of the Sedges and Leguminous functional groups. Meanwhile, the ecological functions including below-ground productivity, soil water holding capacity, and soil organic carbon stocks are greatly decreased along shrubs and forbs encroachment in hillside alpine meadows. Taken together, our results demonstrate that climate warming and overgrazing induced divergent successions to the shrubs-encroached and the forbs-encroached communities both decreased the ecosystem multifunctionality of hillside alpine meadows. The ecosystem multifunctionality of hillside alpine meadow ecosystem might therefore be decreased continuously under ongoing and future climate warming and overgrazing by herbivores. [ABSTRACT FROM AUTHOR]

Plant biomass reveals the productivity and stability of a biotic community and is extremely sensitive to climate warming in permafrost regions, such as the Qinghai-Tibetan Plateau (QTP) in China. However, the response of the plant biomass of different functional groups to rising temperatures in such alpine zones remains unclear. Here, infrared radiators were used to simulate year-round warming on the QTP from 2011 to 2018. During the 8-year warming experiment, air temperature increased by 0.16 °C, while humidity tended to increase by 0.27 % at 20 cm above the ground. However, the rate of the increase in air temperature declined with an increasing number of years. Soil temperature and moisture increased by 1.28 °C and 3.61 %, respectively, on average from 0 to 100 cm below the ground, and the increment of soil moisture tended to rise with increasing depth. At the depths from 0 cm to 20 cm below the ground, soil organic carbon and total phosphorus tended to decrease by 0.79 g/kg and 0.04 g/kg, respectively, while soil total nitrogen tended to increase by 0.04 g/kg. Plant biomass had non-significant responses to warming, but the variation among different plant functional groups was greatest for forbs with the increment being 12.50, 147.97, and 160.47 g/m2 for plants aboveground, belowground, and total biomass, respectively. The ratios of plant total biomass tended to decrease by 2.29 %, increase by 0.60 %, and increase by 1.70 % for grasses, sedges, and forbs, respectively, so warming greatly decreased the proportion of grasses and increased the proportion of forbs in community. Warming weakened the positive correlation of grass biomass with soil temperature and enhanced the negative correlation of grass biomass with soil N and P content, along with weakening the positive correlation of sedge biomass with soil moisture and N content, while enhancing the negative correlation between sedge biomass and soil temperature. Meanwhile, forb biomass was greatly increased by soil temperature in the effects of warming. In conclusion, the 8-year warming produced negative effects on grasses and sedges by increasing soil temperature and N content and thus promoted the growth of forbs, which might induce a shift toward forbs in this community. [Display omitted] • Infrared radiators were used to simulate a year-round warming experiment on a frozen area over 8 years. • The melt of frozen soil caused an increment of soil moisture in deep layers under the 8-year warming. • The increment of soil moisture induced downward transport of soil nutrients and root biomass to deep layers. • The transport of soil nutrients and root biomass altered plant composition among different functional groups. • Eight-year warming might induce shift toward forbs by increasing soil temperature and nitrogen content. [ABSTRACT FROM AUTHOR]

• Precipitation events trigger the pulse N 2 O emissions. • All sizes of precipitation events significantly increase cumulative N 2 O emissions. • Cumulative N 2 O emission after precipitation events parabolically varied with precipitation event sizes. • N addition amplifies the response of cumulative N 2 O emissions to precipitation events. • Precipitation event size plus long-term N addition led to substantial differences in N 2 O emissions. Precipitation events and nitrogen (N) addition play important roles in regulating nitrous oxide (N 2 O) emissions in semi-arid grassland ecosystems. The effects of precipitation events, long-term N addition, and their interaction on N 2 O emissions, however, remain largely unclear. We conducted a mesocosm experiment to examine how long-term N addition (0 and 10 g N m−2 yr−1, from 2011 to 2020) affects N 2 O emission responses to a gradient of manipulated precipitation events (0, 5, 10, 20, and 50 mm). The precipitation events had pulsing effects on N 2 O emissions due to the stimulation of microbial activity and substrate availability. Precipitation events significantly parabolically increased cumulative N 2 O emissions. Long-term N addition substantially enhanced cumulative N 2 O emissions response to precipitation events. The precipitation events and long-term N addition synergistically improved cumulative N 2 O emissions. The water-filled pore space and ammonium nitrogen content were the most important factors driving the temporal dynamics and accumulation of N 2 O emissions following the precipitation events and long-term N addition. Our study indicates that N addition affects the N 2 O emissions responses to precipitation events, which are essential for understanding the response of N 2 O emissions to global change. [ABSTRACT FROM AUTHOR]