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Background and aims: Planting artificial grassland has been widely implemented to restore the extremely degraded alpine meadow. However, the restoration effect of different planting patterns of artificial grassland on the alpine plant and soil is poorly understood. Methods: Three typical native grass species (Elymus nutans, Poa pratensis L. cv. Qinghai, Festuca sinensis) were planted in two patterns: P. pratensis monoculture and mixed sowing containing all three species. The plant, soil physicochemical properties, and soil bacterial community under two different planting patterns in the degraded alpine meadow of Qilian Mountain were evaluated. Results: The aboveground, belowground biomass, coverage, Shannon-winner, and richness diversity of the mixed sowing grassland was approximately 144%, 111%, 113%, 144%, and 205% higher than that of the monoculture grassland. Furthermore, the mixed sowing grassland significantly increased the soil total nitrogen and water content than monoculture grassland. The soil bacterial Chao1 and ACE diversity in mixed sowing was significantly lower than in monoculture grassland. Soil bacterial species network analysis revealed a higher complexity of the mixed plot than the monoculture. The redundancy analysis (RDA) model suggested that plant characteristics caused more variation in the soil bacterial community than in soil physicochemical characteristics. Conclusions: The results show that mixed sowing had more positive restoration on plant and soil than monoculture, and could be recommended for the restoration of degraded alpine meadow. [ABSTRACT FROM AUTHOR]

Backgrounds: Climate change is well-known to alter the structure and function of grassland ecosystems, and multifunctionality contributes to a comprehensive understanding of the impacts of climate change on ecosystem functions. Warming and humidification are predicted to be the climate change trend on the northeastern Qinghai-Tibetan Plateau. However, understanding of how long-term warming and increased precipitation affect ecosystem multifunctionality in alpine meadows is still limited. Methods: Here, we conducted an 8-year field experiment involving warming and increased precipitation in an alpine meadow to explore how warming, increased precipitation, and their interaction affect ecosystem multifunctionality. Results: The results indicated that increased precipitation had a positive effect on ecosystem multifunctionality. However, warming and the interaction of warming and precipitation had no significant effects on it. Warming decreased species richness and plant coverage. Increased precipitation enhanced aboveground carbon (C), nitrogen (N), and phosphorus (P) pools of plant community, and soil moisture, but decreased soil pH. Aboveground P and N pools of plant community and microbial biomass nitrogen (MBN) were important predictors of ecosystem multifunctionality. Conclusion: This study demonstrated long-term increased precipitation can enhance ecosystem multifunctionality by indirectly affecting the individual functions (aboveground P and N pools of plant community and MBN), soil moisture, and pH in an alpine meadow. These findings highlighted that increased precipitation is more critical than warming for enhancing ecosystem multifunctionality in semi-arid alpine meadows. [ABSTRACT FROM AUTHOR]

Aims: Plant functional group (PFG) removal experiments are recognized as an effective way to explore the role of plant diversity and species traits in ecosystem functioning. To minimize soil physical disturbance in plant removal experiments, aboveground parts of targeted plant species are usually cut off without removing their roots from the soil. However, the potential effects of their remaining roots (partially as root litter) on soil nematode communities are still unclear. Methods: We used a three-year PFG removal experiment in a Qinghai-Tibet alpine meadow and set up root-ingrowth mesh bags for one year where removal target plants' roots existed only outside the mesh bags. Results: We found that nematode communities outside the mesh bags had higher nematode channel ratio and lower channel index values, indicating that the root litter outside the mesh bags increased energy flux to bacterial-feeding nematodes over fungal-feeding nematodes. The relative abundance of plant-feeding nematodes was higher inside than outside the mesh bags, probably because of a higher ratio of living roots inside the mesh bags. Non-metric multidimensional scaling showed that the structure of nematode communities inside and outside of mesh bags was generally differentiated except for the no-removal control treatment. Conclusions: We conclude that the remaining roots outside mesh bags could modify the relative abundance ratio of different nematode guilds and soil nematode community structures, suggesting legacy effects of target plants' roots in PFG removal experiments. [ABSTRACT FROM AUTHOR]

Background and Aims: Human-driven nitrogen (N) deposition can alter soil biogeochemistry and plant communities, both critical to soil biota. However, understanding the relative impact of the relationship between nutrient resources and plants on soil communities has been hindered by a lack of experimental manipulations of both factors. We hypothesized that soil nematode communities would be structured predominantly by N addition via overall increased abundance, decreased diversity, and compositional shifts to dominance of r-selected bacterial-feeding nematodes. In contrast, we expected plant effects to be less evident and restricted to nematodes directly associated with plants. Methods: We used a long-term (18-yrs) experiment in moist meadow alpine tundra involving N addition and codominant plant (nitrophilic Deschampsia cespitosa and nitrogen-sensitive Geum rossii) removal. We characterized nematode communities via 18S rRNA metabarcoding and used soil biogeochemistry, plant, and microbial variables to determine factors shaping their communities. Results: The N addition treatment increased overall nematode abundance, decreased diversity, and affected the composition of all nematode trophic groups. Overall, nematode communities shifted to dominance of bacterial-feeding nematode taxa adapted to N-enriched environments. The likely drivers of this shift were increased soil nitrate and lower pH. The direct effects of codominant plants were more limited, with only changes in Geum rossii appearing to affect nematode responses. Conclusion: Overall, nematode communities in N-limited alpine ecosystems are highly sensitive to increases in N availability, irrespective of the nature of N preferences of codominant plants. The resulting nematode community restructuring could signify future shifts in soil functioning throughout alpine landscapes. [ABSTRACT FROM AUTHOR]

Purpose: Sulfur (S) deposition as a global change issue causes worldwide soil acidification, nutrient mobilization and marked changes in plant nutrition. Here, we hypothesize that S deposition would reduce leaf nutrient resorption with this effect varies with yearly fluctuations in precipitation. Methods: In a semiarid meadow exposed to S addition, we determined nitrogen (N), phosphorus (P) and S concentrations and nutrient resorption efficiencies (NuRE) of a grass and a sedge across two years with contrasting precipitation difference. Results: Concentrations of N, P, and S in green and senescent leaves generally increased with S addition across the two years, with the exception of N and P concentrations in green leaves of the grass that showed no response or even decreased with S addition. The coupling relationships between N and P concentrations were stronger in senescent leaves than in green leaves in the wet year. Leaf NuRE decreased with S addition across the two years as driven by increasing soil N, P and S availability. However, NuRE was higher in the wet year due to lower soil nutrient availability herein as compared with the dry year. Conclusions: This study provides new evidence on the role of nutrient resorption in tightening stoichiometric N:P relationships, and that plant nutrient resorption may be favored by higher precipitation to sharpen its tradeoff with soil nutrient availability. [ABSTRACT FROM AUTHOR]

Background and aims: Plant interactions with soil microbes are important drivers of biodiversity and dynamics of alpine plant communities. However, little is known about the effects of these interactions on seed germination and plant establishment of alpine plants under global climate change. We investigated the individual and interactive effects of warming, soil microbes and shrubs on seed germination, survival, and growth of herbaceous species. Methods: We simulated warming and manipulated live and sterile soil microbes and microhabitat in the alpine meadow ecosystem dominated by the shrub (Dasiphora fruticosa) on the Qinghai-Tibet Plateau. We tested the interactive effects of warming, soil microbes, and shrubs on the germination, early life survival, and growth of herbaceous species. Soil microbial communities were determined by high-throughput sequencing. Results: Our results showed that seed germination was significantly reduced under warming; seed germination was higher in live soils than in sterile soils; early life survival was lower under shrub canopies. Additionally, in the warming treatment, the positive effect of soil microbes on seed germination shifted to negative on the early survival of herbaceous species. Furthermore, in the warming treatment, shrubs enhanced the positive effects of soil microbes on seed germination and reduced the negative effects of soil microbes on early survival. The effects of these individual and interactive factors on herbaceous species also depended on species identity and life stages. Conclusion: Overall, our work demonstrates that soil microbes were particularly critical at seed germination stage and plant interactions with soil microbes were significantly altered with experimental warming. [ABSTRACT FROM AUTHOR]

Purpose: Increasing evidence suggests that the role of home-field advantage (i.e. HFA, the specialized decomposers efficiently degrade native litter) in altering decomposition is not restricted to low- or high-quality litter, we thereby hypothesized that different litter carbon (C) fractions may respond differently to these specialized decomposers, blurring the universality of HFA. Additionally, the inherent functional ability of local soil decomposers (i.e. ability) can influence litter decomposition. Methods: We determined how the decomposition of litter dissolved organic C (DOC), total phenolics, cellulose, and lignin responded to HFA and ability in an alpine forest ecotone (i.e. coniferous forest, alpine shrubland, and alpine meadow). Results: HFA influenced labile C, cellulose, and lignin decomposition, and its magnitude and direction depended on initial litter traits, particularly positively with litter C, nitrogen, phosphorus, DOC, and total phenolics concentrations. The effect of ability on labile C loss decreased from forest to meadow, consistent with the functional breadth hypothesis, suggesting that a wider ability from recalcitrant forest litter environment can accelerate labile C loss. The effect of ability on lignin degradation increased from forest to meadow, suggesting that the shift in forest and shrub species to meadow can decelerate biotic lignin degradation. Conclusion: The HFA occurrence is universal during decomposition, along with the distinct abilities were shaped by the altered plant compositions of mountain ecosystem, which has consequences for local plant-soil feedback by affecting litter decomposition. [ABSTRACT FROM AUTHOR]

Background and aims: This study explores trends in soil fungal patterns, potential functions and their responses to carbon and nitrogen applications over alpine grassland succession in the Qilian Mountain area of China. Methods: The soil fungal community was characterized via Illumina sequencing of ITS genes. The FUNGuild database was used to predict functional groups in alpine grassland succession from swamp meadow to alpine meadow and steppe meadow. The levels of soil carbon and nitrogen, vegetation carbon and nitrogen, and soil enzyme activity were also assessed. Results: Soil fungal operational taxonomic units increased from swamp meadow to alpine meadow stage and then reached a relatively stable state in steppe meadow successional stage. This result is consistent with the changing trend of sobs and Chao1 index. Moreover, the soil fungal community differed significantly between different succession stages. During succession, while most phyla of soil fungi followed linear decreasing trends, Ascomycota was the dominant fungal phylum. Its abundance increased significantly, from 60.00% in swamp meadow to 72.26% in steppe meadow. The relative abundances of Pathotroph and Saprotroph fungal functions increased with successional stages, while Symbiotroph did not change significantly. Soil ammonium nitrogen and organic carbon levels dominated the effect on the soil fungal microbial community and functional groups. Conclusion: These findings indicate that the fungal community shifted dramatically in the first stage(swamp to alpine meadow) of succession but then reached a relatively stable state in the second(alpine to steppe meadow) successional stage. The soil fungal function group did not follow the same successional trajectory. Soil ammonium nitrogen and soil organic carbon levels imposed the strongest influence on the fungal community and its function, respectively. [ABSTRACT FROM AUTHOR]

Background and aims: Water and nutrient availability in soil can affect leaf resource-use efficiency. Within a given location and given common soil conditions, variations in root anatomical traits across co-existing species determine nutrient and water supply to leaves. Therefore, leaf resource-use efficiency may be closely related to their root anatomical traits. However, few studies have specifically investigated whether and how root anatomical traits affect leaf resource-use efficiency.Here, we sampled the first two order roots and leaves of 61 herbaceous species in alpine meadows of the Tibetan Plateau. A series of root anatomical traits, leaf photosynthetic nitrogen-use efficiency (PNUE), photosynthetic phosphorus use-efficiency (PPUE) and instantaneous water-use efficiency (iWUE) were examined.We observed that root anatomical traits, PNUE and PPUE differed distinctively among plant functional groups, while no significant differences in iWUE were detected. Principal component analysis (PCA) revealed a two-dimensional trait space: i.e., stele-related dimension and cortex-related dimension. PNUE and PPUE were tightly correlated with cortical traits, and iWUE was closely correlated with stelar traits. Unexpectedly, we found an independent change between PNUE/PPUE and iWUE.These results indicate close relations between leaf nutrient-use efficiency and root cortical traits, as well as between leaf water-use efficiency and stelar traits. Therefore, these findings provide important information to link leaf resource-use efficiency to root anatomical traits.Methods: Water and nutrient availability in soil can affect leaf resource-use efficiency. Within a given location and given common soil conditions, variations in root anatomical traits across co-existing species determine nutrient and water supply to leaves. Therefore, leaf resource-use efficiency may be closely related to their root anatomical traits. However, few studies have specifically investigated whether and how root anatomical traits affect leaf resource-use efficiency.Here, we sampled the first two order roots and leaves of 61 herbaceous species in alpine meadows of the Tibetan Plateau. A series of root anatomical traits, leaf photosynthetic nitrogen-use efficiency (PNUE), photosynthetic phosphorus use-efficiency (PPUE) and instantaneous water-use efficiency (iWUE) were examined.We observed that root anatomical traits, PNUE and PPUE differed distinctively among plant functional groups, while no significant differences in iWUE were detected. Principal component analysis (PCA) revealed a two-dimensional trait space: i.e., stele-related dimension and cortex-related dimension. PNUE and PPUE were tightly correlated with cortical traits, and iWUE was closely correlated with stelar traits. Unexpectedly, we found an independent change between PNUE/PPUE and iWUE.These results indicate close relations between leaf nutrient-use efficiency and root cortical traits, as well as between leaf water-use efficiency and stelar traits. Therefore, these findings provide important information to link leaf resource-use efficiency to root anatomical traits.Results: Water and nutrient availability in soil can affect leaf resource-use efficiency. Within a given location and given common soil conditions, variations in root anatomical traits across co-existing species determine nutrient and water supply to leaves. Therefore, leaf resource-use efficiency may be closely related to their root anatomical traits. However, few studies have specifically investigated whether and how root anatomical traits affect leaf resource-use efficiency.Here, we sampled the first two order roots and leaves of 61 herbaceous species in alpine meadows of the Tibetan Plateau. A series of root anatomical traits, leaf photosynthetic nitrogen-use efficiency (PNUE), photosynthetic phosphorus use-efficiency (PPUE) and instantaneous water-use efficiency (iWUE) were examined.We observed that root anatomical traits, PNUE and PPUE differed distinctively among plant functional groups, while no significant differences in iWUE were detected. Principal component analysis (PCA) revealed a two-dimensional trait space: i.e., stele-related dimension and cortex-related dimension. PNUE and PPUE were tightly correlated with cortical traits, and iWUE was closely correlated with stelar traits. Unexpectedly, we found an independent change between PNUE/PPUE and iWUE.These results indicate close relations between leaf nutrient-use efficiency and root cortical traits, as well as between leaf water-use efficiency and stelar traits. Therefore, these findings provide important information to link leaf resource-use efficiency to root anatomical traits.Conclusion: Water and nutrient availability in soil can affect leaf resource-use efficiency. Within a given location and given common soil conditions, variations in root anatomical traits across co-existing species determine nutrient and water supply to leaves. Therefore, leaf resource-use efficiency may be closely related to their root anatomical traits. However, few studies have specifically investigated whether and how root anatomical traits affect leaf resource-use efficiency.Here, we sampled the first two order roots and leaves of 61 herbaceous species in alpine meadows of the Tibetan Plateau. A series of root anatomical traits, leaf photosynthetic nitrogen-use efficiency (PNUE), photosynthetic phosphorus use-efficiency (PPUE) and instantaneous water-use efficiency (iWUE) were examined.We observed that root anatomical traits, PNUE and PPUE differed distinctively among plant functional groups, while no significant differences in iWUE were detected. Principal component analysis (PCA) revealed a two-dimensional trait space: i.e., stele-related dimension and cortex-related dimension. PNUE and PPUE were tightly correlated with cortical traits, and iWUE was closely correlated with stelar traits. Unexpectedly, we found an independent change between PNUE/PPUE and iWUE.These results indicate close relations between leaf nutrient-use efficiency and root cortical traits, as well as between leaf water-use efficiency and stelar traits. Therefore, these findings provide important information to link leaf resource-use efficiency to root anatomical traits. [ABSTRACT FROM AUTHOR]

Aims: Vegetation in high-altitude regions is hypothesized to be more responsive to increasing atmospheric CO2 concentrations due to low CO2 partial pressure. However, the underlying mechanisms driving this response at an ecosystem scale are poorly understood. We aimed to explore the plant carbon (C) and nitrogen (N) relationships and biomass allocation in response to elevated CO2 and N addition in a Tibetan meadow. Methods: A 5-year manipulation experiment was conducted in an alpine meadow (4585 m above sea level) to explore the responses of plant carbon (C), nitrogen (N), and biomass dynamics, as well as their allocation schemes, to elevated CO2 (from 380 ppm to 480 ppm) and N fertilization. Results: Elevated CO2 alone significantly enhanced aboveground plant biomass by 98%, exhibiting a stronger CO2 fertilization effect than the global average level (20%) for grasslands. Elevated CO2 favored N accumulation in aboveground parts despite the declined concentration. Nitrogen fertilization alleviated the N constraints on CO2 fertilization effects, which strengthened C sequestration capacity for the aboveground plant tissues. Moreover, our results indicate a decoupling between C and N cycles in alpine ecosystems under elevated CO2, especially in the N-enrichment environments. Conclusions: Overall, this study shows a high sensitivity of aboveground plant biomass and decoupled C-N relationships under elevated CO2 and N fertilization for high-elevation alpine ecosystems, highlighting the need to incorporate altitude effects into Earth System Models in predicting C cycle feedbacks to climate changes. [ABSTRACT FROM AUTHOR]

Plant diversity is assumed to positively influence the diversity of soil biota. However, empirical studies on the linkages between diversities of plants and soil biota under fertilization revealed inconsistent results. In addition, the relative importance of direct and indirect impacts of fertilization on plant and soil biotic communities is still unclear. Taking advantage of a 13-year fertilization experiment with nitrogen and phosphorus addition in an alpine meadow, we measured community composition of plants, bacteria, fungi, and nematodes, analyzed direct and indirect effects of fertilization on these communities, and investigated relationships between their community structures. We found that fertilization significantly increased plant biomass and nematode abundance, and decreased their α-diversities. Microbial biomass carbon and fungal α-diversity increased with low levels of fertilization but decreased at the highest level of fertilization. However, structural equation modelling showed that fertilization had minor direct effects on soil biota except for bacteria. Instead, fertilization indirectly influenced fungi and nematodes through plant α-diversity. Furthermore, β-diversity (community dissimilarity) was positively correlated between plants and soil biota, even after controlling for fertilization effects. Our study provides empirical evidence showing the linkage of both α- and β-diversities between plants and soil biota, and implies the potential of plants for regulating soil biotic communities under long-term fertilization. These findings can help us predict changes in soil biota under nutrient-enrichment scenarios in alpine meadows with data on plant diversity and community composition. [ABSTRACT FROM AUTHOR]

Zhang et al. ([29]) determined that linkages between community assembly processes and the abundance of soil nematode communities under nutrient enrichment may play a major role in the C cycling of meadow steppe ecosystems. China's meadow grasslands possess a total area of some 1.1 million km SP 2 sp , including meadow steppes (60,851 km SP 2 sp ), lowland meadows (252,196 km SP 2 sp ), montane meadows (167,189 km SP 2 sp ), and alpine meadows (637,206 km SP 2 sp ) (Liao and Jia [15]). 1 Outline map of the Chinese meadow steppe vegetation (adapted from Li et al. [11]) Of the 15 papers presented in this Special Issue, 12 concern meadow steppe communities at local and regional scales, based on either long-term stationary manipulative experiments, or off-site incubation tests, and transect surveys. Overgrazing has long been regarded as the most significant factor causing grassland degradation in China, while cultivation of grasslands has been most substantial in the meadow steppe region of Inner Mongolia and meadows in northeast China. [Extracted from the article]

Purpose: In nitrogen (N)-fertilized grasslands, mowing removes large quantity of nutrients from ecosystems due to plant biomass removal at higher levels. This study tested the hypothesis that if mowing could counteract the synergistic interactions of exogenous zinc (Zn) and N supply on plant Zn uptake. Methods: Our hypothesis was tested with three dominant species (Leymus chinensis, Carex duriuscula, and Stipa baicalensis) in a field experiment exposed to Zn addition, N addition and mowing treatments. A pot experiment using a low-Zn soil was further conducted to explore mechanisms of N-driven changes in plant-soil Zn dynamics. Results: Zinc addition increased soil available Zn across all treatments. However, effects of Zn addition on plant Zn uptake were treatment- and species-specific given by higher Zn contents in L. chinensis under N addition, in C. duriuscula under mowing, and in S. baicalensis under mowing and N addition. Nitrogen addition synergistically interacted with Zn addition to increase Zn uptake of L. chinensis. Meanwhile, N addition reduced Zn uptake of C. duriuscula without Zn addition, mainly due to plant biomass suppression in the presence of more dominant L. chinensis. Mowing counteracted the synergistic effect of combined N and Zn addition on Zn content of L. chinensis through biomass removal and lowering soil moisture. Conclusion: Our results indicated that plant Zn uptake was mainly driven by soil Zn availability and species-specific responses of biomass to N addition and mowing. Moreover, counteractive mowing effect on the synergisms between Zn and N addition might necessitate grassland Zn fertilization. [ABSTRACT FROM AUTHOR]

Aims: Biological nitrogen fixation (BNF), a function performed by diazotrophic microbes, plays an essential role in nitrogen (N) bioavailability in terrestrial ecosystems. However, little is known about the effects of meadow degradation on soil BNF and diazotrophic communities in alpine meadows. Methods: We investigated changes in soil BNF and their potential drivers in alpine meadows along a degradation gradient on the Tibetan Plateau (non-degraded, lightly degraded, moderately degraded, and severely degraded meadows) using real-time quantitative PCR and amplicon sequencing. Results: Soil BNF rates decreased significantly along the meadow degradation gradient with a range of 17.34–79.84 nmol C2H4 g−1 dry soil d−1 across all sites. The highest BNF rate in the non-degraded meadow was 1.5–4.6-fold higher than that in the degraded meadows. The abundance and diversity of diazotrophs measured by nifH abundance and Shannon diversity was also decreased in the degraded meadows, accompanied by decreases in plant biomass, soil moisture, and nutrient content (C, N). Soil BNF rate was correlated with plant biomass, soil nutrient content, and diazotrophic abundance (including Nostoc, Scytonema, Rhodopseudomonas, and unidentified genera within the Rhizobiales and Proteobacteria). The community composition of diazotrophs differed markedly among sites with different levels of degradation, with both autotrophic (Cyanobacteria) and heterotrophic (Proteobacteria) diazotrophs contributing significantly to BNF. The plant functional groups, particularly the sedge family, were the primary drivers of soil BNF rates via mediating soil moisture, nutrient content (dissolved organic C and N), nifH gene abundance, and diazotrophic community composition. Conclusions: Our results reveal the main drivers of decreased BNF during alpine meadow degradation and emphasize the importance of plant functional groups in shaping the diazotrophic community and regulating the BNF rate. This information can be applied to the restoration of degraded meadow ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Livestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate. Methods: In situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique. Results: We found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools. Conclusions: In this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate. [ABSTRACT FROM AUTHOR]

Aims: Changes caused by single herbivore species grazing to soil and plant interfaces can significantly affect the leaf litter decomposition rates within ecosystems. However, we intended to study how grazing by multiple herbivore species regulate the litter decomposition process and associated soil or plant properties in Leymus chinensis dominant meadow steppe. Methods: Two consecutive randomized field experiments were conducted between May 2017 and May 2019: 1) a grazing experiment with four (control or no, sheep, cattle, and mixed (sheep + cattle)) grazing treatments to explore the effects of moderate grazing on soil properties and L. chinensis litter quality and 2) the litter decomposition experiment to evaluate the decay rate in grazed or non-grazed litter by using litter bag technique. Results: Litter decay rate was the highest in mixed grazed litter as compared to litter grazed by individual herbivore species. Both herbivore grazing and incubation time affected decay rate of L. chinensis litter by modifying soil moisture and nitrogen (N) content, as well as, litter N and lignin contents. Plant litter quality has been displayed to be a dominant regulator of litter decay rate than soil physical or chemical properties in mixed grazed litter. Conclusions: Livestock diversification benefited litter decomposition indirectly by modifying plant litter quality with time. Therefore, herbivore assemblages should be given more importance in future research on litter decomposition process to mediate nutrient cycling in grassland. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the effects of livestock grazing on the ecosystem biomass and soil nitrogen processes of grassland ecosystems is critical to improving knowledge on the mechanisms underlying grassland degradation and accurately assessing the influence of grazing management on grassland functions. Methods: We examined the interannual patterns of ecosystem biomass and soil nitrogen mineralization in response to cattle grazing in a Chinese meadow steppe. The soil core incubation method was employed for soil N transfer estimation, whilst the fumigation extraction method, a modified Baermann funnel method and harvest method were used for various measurements of ecosystem biomass parameters. Results: We found that cattle grazing caused consistent significant increases in soil temperature, irrespective of the stocking rate and year, whereas significant effects on soil moisture and edaphic properties were observed only in individual years and/or at specific stocking rates. Consistent positive effects at moderate stocking rates were observed for aboveground net primary production and soil nematode biomass in all study years. The across stocking rate pattern of N mineralization in response to cattle stocking appeared to be year-specific, although negative effects were found in most cases. In contrast, the interannual pattern of N mineralization was determined principally by the interannual patterns in precipitation and soil moisture and was much less affected by cattle grazing. Conclusions: Soil N mineralization in this meadow steppe was affected by cattle grazing via two major mechanisms, i.e., its effects on the aboveground net primary production (ANPP) and thus the quantity of plant litter input into the soil and its effects on soil temperature and moisture. Overall, our study spanned the longest consecutive years with the broadest range of stocking rates thus far of its kind, which revealed for the first time that the soil nitrogen mineralization pattern with respect to stocking rate was year-specific. Our findings have important implications for adaptive management and sustainable utilization of Chinese grasslands. [ABSTRACT FROM AUTHOR]

Aims: Soil nematodes, as key bioindicators, play crucial roles in soil ecological process. Management of grasslands, such as meadow steppes in northeast China, is often done by mowing, which has an impact on soil nematode communities. However, few studies have explored effects of mowing frequency on the community structure and biomass of soil nematodes. Methods: Routine field and laboratory methods concerning plant community, soil properties, and soil nematodes were applied in this study. Soil nematode community structure was analyzed by using nonmetric multidimensional scaling (NMDS) and principal component analysis (PCA). The relationships between nematode genus and biotic and abiotic factors were analyzed by redundancy analysis (RDA). Results: High mowing frequency significantly reduced abundance, biomass, and functional or metabolic regimes of soil nematodes in this ecosystem, whereas moderate mowing frequency enhanced those indices and regimes. Conclusions: Our findings showed that changing patterns in nematode indices across the mowing frequency conformed with the intermediate disturbance theory. Variations in soil nematode community were related to changes in belowground biomass, aboveground litter, soil available nitrogen and acidity, and the effects of edaphic and vegetal traits appeared to be trophic or genus-specific. This study has potential benefits for grassland restoration in northeast China. [ABSTRACT FROM AUTHOR]

Background and aims: Soil microorganisms play key roles in soil nutrient turnover and plant community composition; however, the soil microbial community composition and species diversity are often influenced by nutrient enrichment which may affect how soil microbes influence nutrient cycles and the plant community structure. The resistance of soil fungal and bacterial communities to nitrogen (N) and phosphorus (P) additions and whether the responses of the soil microbes and the plant community are simultaneous in a N-limited temperate meadow ecosystem are still unclear. Methods: We carried out a 7-year experiment with N and P additions in a temperate meadow. The community structures of soil bacteria and fungi were examined based on high-throughput sequencing targeting the 16S rRNA and ITS genes, respectively. Results: Nitrogen addition did not influence the community composition or species richness of bacteria, but it did alter the soil fungal community composition and increased fungal operational taxonomic unit (OTU) richness. Phosphorus addition significantly altered the soil fungal and bacterial community compositions, decreased the richness of bacterial OTUs, and increased the OTU richness of fungi. Proteobacteria (38.5%) and Acidobacteria (22.3%) were the most dominant bacteria. Ascomycota were the dominant fungi (42.6%) across all samples. The enrichment of available P in the soil due to P addition reduced the bacterial β-diversity, while the β-diversity of soil fungi was mainly influenced by the concentrations of soil N and P, as well as soil moisture. Conclusions: The sensitivity of soil fungi and bacteria to P addition was stronger than that of N addition, and the response of the soil microbes to N and P additions was more sensitive than that of the plant community. Our results highlight the unequal sensitivity of the soil fungal and bacterial community composition and structure to N and P additions, thereby causing changes in above and belowground community composition and structures in the studied temperate meadow ecosystem. [ABSTRACT FROM AUTHOR]

Background and aims: Microorganisms play a vital role in regulating soil phosphorus (P) dynamics in terrestrial ecosystems. Here, we investigated the response of soil microbial P cycling potential traits to nitrogen (N) addition via metagenomics and the relationship between microbial potentials and soil P dynamics. Methods: Topsoil (0–10 cm) samples were collected from experimental soil that had been maintained for 3 years with low and high level of N addition in an alpine meadow of the Qinghai-Tibet Plateau. Soil microbial functional genes and P fractions were determined. Results: The soil available P and microbial biomass P were significantly affected by N inputs and significantly associated with soil properties (including soil pH, alkaline phosphatase activity, and soil total N and NO3−-N contents). Meanwhile, high N input decreased the relative abundance of the pstS gene, and low N input reduced the relative abundances of phoB, ugpQ and C-P lyase genes. We further found that the pstS gene was a determinant of soil microbial biomass P and significantly correlated with soil pH. Moreover, Alphaproteobacteria with C-P lyase and Actinobacteria related to alkaline phosphatases and phosphate-specific transport were the most abundant taxa but not affected by N input. Conclusions: Short-term high N input could alter soil P dynamics and microbial functional genes. Although there were relationships between the pstS gene, microbial biomass P and soil pH, the microbial functional gene abundance was less important than soil properties in regulating soil P dynamics. [ABSTRACT FROM AUTHOR]

Aims: Reveal the soil organic carbon (SOC) stock change in the Qinghai-Tibetan Plateau (QTP) alpine wetlands in the past fifty years. The Qinghai-Tibetan Plateau (QTP) has a large area of alpine marshland and wet meadows. Artificial drainage, overgrazing and climate change have caused severe degradation of the alpine wetlands. However, little is known about the effects of wetland degradation on SOC stock, and studies only focused on the Zoige marshland, the biggest marshland of China. Direct SOC observations from the extensively distributed wet meadows remain scarce. Methods: SOC in the soil surface layer (0–50 cm) were investigated at four wetland sites where degradation has continued for decades. One site is in marshland, and three are in wet meadows of the QTP. Using datasets from the literature and the field measurements of the present study, we estimated the loss of alpine wetland SOC. Results and conclusions: Initially, marshland degradation to wet meadows prompted the accumulation of SOC; however, grazing in wet meadows reduced SOC accumulation. Wetland degradation to dried meadows led to a much greater SOC loss than that in the initial degradation stage, and grazing exacerbated the loss of SOC. An exponential decay rate of SOC was found in the grazed dried meadows. The wetlands of the QTP, have lost 141 ± 25 Tg in 1966–2016, representing 15% of the SOC stock. [ABSTRACT FROM AUTHOR]

Background and aims: Root-associated fungi link resource fluxes between the soil and roots, thus influencing plant growth and ecosystem function. However, at present, the impact of global warming on these fungi and their plant host specialization, especially in ecosystems on the Qinghai-Tibetan Plateau is obscure. Methods: Here, pot experiments were conducted to examine the root-associated fungal community structure of 14 host plant species undergoing two years of experimental warming on the Qinghai-Tibetan Plateau. Infrared heaters were used to raise the soil temperature to 2.0 ℃ higher than the relative ambient temperature. Subsequently, the endophytic and rhizoplane fungal communities were explored by sequencing the fungal internal transcribed spacer (ITS) region. Results: A total of 1564 OTUs were identified, which were dominated by ascomycetes (82.71%). Similar root-associated fungal diversity and community composition were identified under ambient and warming environments. The root-associated fungal community composition significantly varied among different host plant species, and this dissimilarity was enhanced under experimental warming. Root N concentration was essential in shaping the structure of the root-associated fungal community. Conclusions: Although the root-associated fungal community was resilient to short-term warming, our study highlights that climate warming can induce higher host specificity of root-associated fungal communities in the alpine meadow ecosystem. [ABSTRACT FROM AUTHOR]

Aims: Viable seeds in herbivore dung constitute the dung seed bank, and the contribution of livestock dung to this seed bank in grazing pastures is often overlooked. Grazing season (warm and cold), seed characteristics (size and shape), and forage preference are the main factors that affect the size and composition of the dung seed bank and ultimately affect grassland ecology. However, how these three factors interact is unclear. Methods: We collected yak dung as well as seeds of the common plant species from warm- and cold-season alpine meadows in northeastern Qinghai-Tibetan Plateau, and explored how grazing season (warm and cold), seed characteristics (size and shape) and foraging preferences (temporary cages method) affects yak dung seedling density, richness and diversity in an alpine pasture. Results: Forty-three plant species (mainly perennials) germinated from yak dung. Dung seedling density, richness, and diversity did not differ significantly between the two grazing seasons. Small to medium-sized spherical seeds (seed size < 10 mg, shape index < 0.5) had the greatest germination potential. Conclusions: Yaks vary their forage preference depending on the season (phenological period), and endozoochory occurs throughout both grazing seasons. Seed shape and size directly regulate the dung seedling density, richness, and diversity. Dung seedlings increase the heterogeneity of the aboveground vegetation near the microsites of the dung pieces and therefore promote grassland patching. Our study demonstrates that grazing season, seed characteristics, and yak forage preferences affect the dung seed bank in grazing ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims: Dissolved organic nitrogen (DON) has been increasingly recognized as a crucial component of the terrestrial nitrogen (N) cycle that regulates the ecosystem feedback to climate change. Yet, little information is available about the factors that control soil DON in the alpine ecosystems of the Tibetan Plateau, a region that is extremely sensitive to climate change. Methods: Here, we examined the relationship between DON and climate, plant, and soil attributes along a precipitation gradient in five alpine ecosystems (alpine wetland, alpine meadow, alpine shrub, alpine steppe, and alpine desert) across 20 sites that were up to 4000 km apart on the Tibetan Plateau. Results: Results showed that soil DON concentration varied significantly across these alpine ecosystems, and had a positive relationship with mean annual precipitation. Belowground biomass, soil moisture, micro biomass carbon (MBC), and soil total phosphorus (TP) explained 84% of the variation in DON concentrations. The percentage of DON in soil total dissolved N (TDN) varied with vegetation type, with the lowest percentage observed in the alpine meadow (52%) and the highest in the alpine desert (77%), indicating the slow turnover of DON into inorganic N in systems with low litter input and microbial activity. Conclusions: Precipitation and plant biomass input determine the concentration and turnover of soil DON on the Tibetan Plateau. A warmer and wetter climate that has been predicted for the Tibetan grasslands may lead to a larger and more active DON pool. [ABSTRACT FROM AUTHOR]

Aims: Plant diversity and coverage on the basidiomycete fungus Floccularia luteovirens fairy rings are higher than those outside of the fairy rings, indicating a favorable role of F. luteovirens in the growth of alpine meadow plants on the Qinghai-Tibet Plateau. However, the underlying physiological and molecular mechanisms of F. luteovirens-mediated plant growth and environmental adaptation remain largely unclear. Methods: Here, the growth and metabolic profiles of two alpine meadow plants which are the dominant plant species growing on F. luteovirens fairy rings (Kobresia humilis and Oxytropis coerulea), were investigated via physiological and metabolomic analyses. Results: F. luteovirens increases nutrient element accumulation in plants and improves the growth of the aboveground tissues but reduces the root growth of alpine meadow plants. Metabolomic analysis revealed that F. luteovirens reprograms carbohydrate and amino acid metabolism and affects the levels of organic acids and flavonoids, thereby modulating the growth and environmental adaptation of plants. Conclusions: Together, these results suggest that F. luteovirens promotes aboveground growth by modulating nutrient uptake and regulating metabolism in plants. These findings help to further elucidate the role of this edible mushroom fungus in influencing alpine meadow vegetation. [ABSTRACT FROM AUTHOR]

Aims: Root dynamics plays a fundamental role in determining carbon allocation and other main ecological processes in grasslands. Understanding the responses of root activities to ongoing warming in grazed alpine meadows enable us to predict the potential changes in the carbon budget and ecosystem functions in alpine regions. Methods: We conducted a controlled 4-year field experiment with warming and grazing in an alpine meadow on the Qinghai-Tibetan Plateau. Our objective was to explore the responses of root standing crop, production, mortality and turnover rate to warming and grazing using minirhizotrons. Results: Warming only significantly inhibited root mortality while grazing promoted all the four root metrics, which were also significantly influenced by the interaction of warming and grazing. Warming oppositely affected the four metrics under grazing versus non-grazing conditions. It significantly reduced root mean standing crop, annual production and mortality without grazing, but significantly stimulated only mean standing crop under grazing. Grazing had significantly negative and positive effects on mean standing crop in the no warming and warming plots. It promoted annual root production and mortality regardless of warming, whereas the effects were significant only under warming condition. Moreover, grazing significantly increased turnover rate in no warming plots but slightly decreased it in warming plots. Conclusions: These findings highlight the non-additive interactions on the alpine meadow root dynamics between warming and grazing. Therefore, grazing regimes should be considered to better model the ecosystem feedback to global warming and to improve the prediction of future ecosystem functions. [ABSTRACT FROM AUTHOR]

Aims: Carbon stocks in alpine meadows on the Qinghai-Tibetan Plateau are being threatened by increases in livestock herding practices. However, the extent to which current fast-growing disturbance by Tibetan pig rooting alters carbon stocks in these meadows and the underlying processes are still unclear. Methods: We conducted a 3-year study in meadows with three different plant communities on the southeast Qinghai-Tibetan Plateau to explore the effects of rooting by Tibetan pigs on carbon stocks. Results: Rooting by Tibetan pigs decreased plant biomass carbon (PBC), soil organic carbon (SOC), microbial biomass carbon (MBC), and ecosystem carbon (EC) by 91.25%, 30.57%, 28.94%, and 40.47%, respectively. Soil moisture (SM) was the most significant factor negatively associated with PBC, SOC, and EC. Additionally, a decreased SM by rooting also exerted an indirect effect on MBC by directly reducing plant biomass. Conclusions: Rooting by Tibetan pigs diminishes carbon stocks by decreasing SM, threatening carbon stocks stored in alpine meadows. Thus, caging or reducing the breeding number of Tibetan pigs combined with restoring soil water levels would be effective ways to recover and maintain carbon stocks in alpine meadows on the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Background and aims: Seasonal grazing is a traditional grassland management practice in alpine swamp meadows on the Tibetan Plateau, but little information is available on the interactions between plant diversity and soil carbon and nitrogen sequestration in warm- and cold- season grazed alpine swamp meadows. Methods: A multisite survey was conducted to investigate the plant characteristics and soil properties of Tibetan alpine swamp meadows under warm-season grazing (WG) and cold-season grazing (CG). Results: Our study showed that plant biomass, litter mass, soil water content (SW), soil available nitrogen, soil microbial biomass carbon and nitrogen were significantly lower in the WG meadows than in the CG meadows (P < 0.05). However, plant diversity, species richness and the evenness index tended to increase in the WG meadows. Soil C and N storage were significantly lower in the WG meadows than in the CG meadows (P < 0.01). Grazing-induced changes in SW, plant diversity, plant biomass and litter mass were the major factors resulting in the decrease in soil C and N storage. Conclusions: Our results indicate that warm-season grazing is beneficial for species diversity conservation, whereas cold-season grazing is suitable for soil C and N sequestration in alpine swamp meadows. Grazing-induced changes in litter mass greatly contributed to variations in plant diversity and soil C and N storage. In view of the accelerated vegetation and soil degradation in alpine grasslands, periodic warm- and cold-season grazing strategies should be considered to maintain alpine swamp meadow sustainability. [ABSTRACT FROM AUTHOR]

Background and aims: In recent decades, an increasing proportion of alpine shrub meadow has become severely degraded owing to the combined effects of global climate warming and rodent infestation, with significant impacts on soil water retention. The present paper investigates the patterns and controlling factors of soil water retention of alpine shrub meadow under different degrees of degradation, to help inform decisions on the management of degraded alpine shrub meadow. Methods: Four degradation stages were defined: non-degradation (ND); light degradation (LD); moderate degradation (MD) and higher degradation (HD). Pearson correlation and redundancy analysis were used to examine the relationships between soil physical properties and soil hydraulic properties. Results: Sand content increased while clay content decreased with increasing degree of degradation. In HD treatment, the available nitrogen and soil bulk density of surface soil layer was significantly lower than that in the other three stages, whereas the soil organic matter content and soil total porosity of surface soil layer was increased significantly, the soil compaction of 0–10 cm soil depth in HD was reduced significantly. The soil water retention of 0–60 cm soil depth first decreased and then increased with increasing degradation, with the maximum values occurring in HD, and the soil organic matter has an overwhelming effect on soil water retention than soil texture. Conclusions: As the degree of degradation increased, the surface soil structure deteriorated, and available nitrogen reduced while soil organic matter increased sharply in higher degradation, which leads to the highest soil water retention in higher degradation. Our results suggested that the soil water retention in degraded alpine grassland was largely determined by soil organic matter, and the soil organic matter parameters should be incorporated in hydrological models of degraded alpine ecosystem. [ABSTRACT FROM AUTHOR]

Aims: Fencing to prevent livestock grazing has widely been implemented to restore vegetation and soils of degraded alpine meadows on the Zoige Plateau in recent decades, but its efficacy is still unclear. This study was designed to investigate the responses of plant community and soil properties to long-term fencing. Methods: We surveyed vegetation structure and production, soil physical and chemical properties in three sites, each having paired adjacent plots (i.e. one was fenced for 11–17 years and the other was allowed for regular grazing). Results: Long-term fencing resulted in species loss at the community level and decreased plant species richness at the plot level. Fencing increased aboveground plant biomass and plant litter accumulation but reduced root biomass, and in particular it dramatically increased the aboveground biomass of grasses at the expense of legumes and sedges. Moreover, fencing decreased soil organic carbon and total N concentrations, and soil bulk density, but increased soil water infiltration rate, soil total P and soluble N concentrations, while soil soluble P concentration remained unchanged. Conclusions: These results indicate that long-term (> 11 years) fencing is not beneficial to plant diversity and soil organic carbon sequestration of the Zoige alpine meadows. [ABSTRACT FROM AUTHOR]

Background and aims: Over-grazing have significantly altered above- and belowground functions in terrestrial ecosystem. However, the influence of grazing intensity on plant-soil stoichiometric relations in alpine ecosystems remains unclear. Methods: We investigated the responses of plant-soil nutrient stoichiometric relationships to four grazing intensities (un-grazing (UG), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) in an alpine meadow on the eastern Tibetan Plateau. We measured carbon (C), nitrogen (N), phosphorus (P) and potassium (K) concentrations and their ratios in plants and soils in the peak growing season after three years of yak-grazing. Results: Compared to UG and LG plots, heavier grazing intensity at community levels and taxonomic groups decreased plant C and K concentrations by 7.6–10.5% and 17.6–21.3%, respectively, while grazing did not significantly influence plant N and P concentrations. Grazing intensity altered plant C:N and C:P ratios but not C:K and N:P ratios. By contrast, grazing intensity had no significant effects on soil nutrients and stoichiometry. Thus, the differential responses of plant and soil nutrients to grazing intensity caused that plants were more sensitive to grazing than soils. Conclusions: Our results confirm that grazing intensity has differential effects on plant and soil nutrients, implying that plant nutrients do not covary with soil nutrients under changing grazing intensity and challenging the past positive relations between plant and soil nutrients. Further long-term grazing experiments are required to understand the drivers of grazing effect on plant-soil nutrient interactions. [ABSTRACT FROM AUTHOR]

Background and aims: Long-term nitrogen (N) addition can affect soil organic carbon (SOC) pool within different soil fractions with different turnover rates. However, the mechanisms of these effects, particularly in alpine grassland ecosystems, are not clear. Methods: We studied the responses of SOC content in different soil fractions to N addition based on a six-year N addition field experiment in an alpine meadow ecosystem on the Tibetan Plateau. We measured soil chemical and microbial properties, and SOC content in bulk soil, particular organic matter (POM) and mineral-associated organic matter (MAOM) fractions in response to N addition. Results: N addition increased soil N availability, decreased soil pH and microbial biomass, but had minimal effect on plant biomass, soil enzyme activity, and SOC content in bulk soil. With increasing levels of N addition, SOC in the POM fraction (POC) showed a significant negative trend, while SOC in the MAOM fraction (MAOC) did not change significantly. Conclusions: As plant biomass input and soil enzyme activity were not significantly altered with N addition, the decline in POC was likely caused by changes in microbial physiology (carbon use efficiency), while the insignificant change in MAOC may be determined by the balance between input (from microbial necromass) and output (from microbial decomposition). Taken together, our study showed that the less-protected POC fraction is more vulnerable to N addition than the more-protected MAOC fraction in the alpine grassland. This finding may improve the prediction of soil C dynamics in response to N deposition in alpine grassland ecosystems on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Background and aims: Responses of grassland carbon (C) cycling to changes in precipitation and land use remain a major uncertainty in model prediction of future climate. It remains even far from clear on how does clipping regulate the response sensitivity of grassland C sequestration to precipitation change. Methods: We conducted a manipulative field experiment with five precipitation treatments (1/12P, 1/4P, 1/2P, 3/4P, P, and 5/4P, where P is the growing season precipitation) interacting with clipping treatments in an alpine meadow to examine net ecosystem C uptake and its associated processes in response to clipping and precipitation gradients as well as their interaction. Results: (1) clipping significantly increased soil temperature in 2016 and 2017, while had no effect on soil moisture; (2) clipping also stimulated the net ecosystem productivity (NEP) and gross ecosystem productivity (GEP) during the two growing seasons; (3) although there were no significantly interactive effects of clipping with precipitation changes, clipping increased the response sensitivity of C uptakes to soil moisture changes. NEP increased more with soil moisture under clipping (0.21 μmol m−2 s−1 v/v−1) than unclipping treatments (0.11 μmol m−2 s−1 v/v−1). This was due to the compensatory growth and the positive effect of clipping on soil temperature, which stimulated plant growth and productivity. Conclusions: Our findings suggest that clipping will aggravate grassland's sensitivity to precipitation change. These findings highlight the important role of land use change in regulating ecosystem C sequestration under further climate conditions in an alpine meadow. [ABSTRACT FROM AUTHOR]

Background: Alpine ecosystem underlain by permafrost is considered as one of the most vulnerable ecosystems to disturbance, especially the alpine grassland on the Tibetan plateau with an altitude above 4000 m. Plateau pika (Ochotona curzoniae) burrowing can create distinctive bare grounds and cause micro-topographical heterogeneity in alpine grasslands. The burrowing-induced changes in microtopography may directly alter plant and soil interactions as well as ecosystem carbon cycle, which have rarely been studied in Tibetan alpine grasslands. Methods: To test the responses of ecosystem respiration (Re) to pika burrowing-induced changes in microtopography, we investigated plant characteristics, soil properties and Re from the bare grounds and vegetated grounds in the alpine meadow and steppe on the Tibetan Plateau. Results: Our study showed that vegetation cover, species richness, plant biomass, soil moisture (SM), soil organic carbon (SOC), total nitrogen (STN), soil microbial biomass carbon (MBC) and nitrogen (MBN) in the bare grounds were significantly lower than in the vegetated grounds in both alpine meadow and alpine steppe (P < 0.05). However, soil temperature and inorganic nitrogen tended to increase in the bare grounds. The growing season Re was significantly lower in the bare grounds than that in the vegetated grounds (P < 0.01). Pika burrowing had negative effects on Re and its temperature sensitivity in both alpine vegetations (P < 0.05). The relative changes in Re due to burrowing-induced changes in microtopography were positively correlated with the burrowing caused changes of AGB, BGB, SOC and MBC (P < 0.05). Pika burrowing-induced changes in soil temperature, soil moisture, plant biomass and microbial biomass are the major factors for the decrease of Re in the bare grounds. Conclusion: In view of the large number of pika burrows in the alpine grasslands and the loss of soil organic carbon due to pika bioturbation, the impacts of pika burrowing-induced changes in microtopography on Re must be considered in predicting the carbon cycle in alpine grasslands. [ABSTRACT FROM AUTHOR]

Background and aims: In addition to improving vegetation, grazing prohibition changes the soil micro-environment. Soil enzymes and microbes, which are the chief constituents responsible for mediation of most of the processes involved in energy and material fluxes of ecosystems, are very sensitive to changing environments. This study aimed to illustrate the effects of grazing prohibition on vegetation and soil enzyme characteristics, and to elucidate the responses of soil fungal and bacterial function and community composition on grazing prohibition for 10 years in a Qinghai-Tibetan alpine meadow. Methods: About 6 hm2 lightly degraded alpine meadows were selected in 2006, and half of which were fenced to completely prohibit grazing throughout the year, while the other half were subjected to free yak grazing. Four different plots in each site were selected as experimental fields in 2016. Soil microbial characteristics were analyzed by high-throughput gene detection. Results: Grazing prohibition had no significant impact on vegetable Shannon-Wiener diversities or below-ground biomass, but dramatically changed the above-ground biomass and soil phosphatase activity. In the Qinghai-Tibetan alpine meadow, bacteria are dominant members of the soil microbial community. Grazing prohibition significantly increased the fungal species diversity and the abundance of pathotrophs, saprotrophs and symbiotrophs, while it had no effect on soil bacterial diversity and functional structure. A total of 100.0% of the variations in fungi and bacteria could be explained by plant variables. The reciprocal action among plant biomass (i.e. above-ground biomass, below-ground biomass), plant diversities (i.e. Shannon-wiener diversity, species number, coverage) and species important value have a great impact on soil microbial composition variations. Conclusion: Long-term grazing prohibition restrained the phosphatase activity and increased the abundance of pathotrophic fungi but had no effect on the abundance of functional bacteria, which participate in the soil biogeochemistry cycling process. Grazing prohibition for 10 years did not improve the community structure of functional microorganisms related to carbon, nitrogen and sulfur, and appropriate grazing could maintain the sustainable utilization of grassland resources. [ABSTRACT FROM AUTHOR]

Aims: Soil aggregates constitute spatially-separated microbial habitats and architectural units for biogeochemical reactions. However, little is known about how aggregates varying in size can affect soil carbon (C) storage and mediate the direction of plant-soil interactions. Methods: In a meadow steppe, we assessed soil aggregate C storage affected by nitrogen (N) addition and mowing and to what degree plant-soil interactions differed among soil aggregate-size classes. Results: Nitrogen addition increased plant biomass, soil C concentration in macroaggregates and relative abundance of bacteria, but decreased fungal relative abundance and the activity of oxidative enzymes. However, mowing counteracted N effects on plant productivity and enzyme activity. In macroaggregates, close linkages with plant biomass and species richness were found for soil available nutrients and ratio of fungi to bacteria (F:B ratio). In contrast, strong physical protection and restricted fungal dominance and activity contributed to C stabilization in microaggregates, where plant community and soil properties were less linked with each other. Conclusions: Our study clearly demonstrated that stronger plant-soil linkages occurred in macro- vs. microaggregates. This linkage was associated with a rise in plant biomass and soil C accumulation but a drop in F:B ratio in macroaggregates under N addition. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the influences of environmental variation and anthropogenic disturbance on soil respiration (RS) is critical for accurate prediction of ecosystem C uptake and release. However, surprisingly, little is known about how soil respiration and its components respond to grazing in the context of global climate change (i.e., precipitation or nitrogen deposition increase). Methods: We conducted a field manipulative grazing experiment with water and nitrogen addition treatments in a meadow grassland on the Songnen Plain, China, and assessed the combined influences of grazing and global change factors on RS, autotrophic respiration (RA), and heterotrophic respiration (RH). Results: Compared with the control plots, RS, RA and RH all exhibited positive responses to water or nitrogen addition in the wet year, while a similar effect occurred only for RH in the dry year. The responses of RS to precipitation regimes were dominated by both frequency and amount. However, grazing significantly inhibited both soil respiration and its components in all subplots. Further analysis demonstrated that the plant root/shoot ratio, belowground biomass and microbial biomass played dominant roles in shaping these C exchange processes. Conclusion: These findings suggest that changes in precipitation regimes, nitrogen deposition, and land utilization may significantly alter soil respiration and its component processes by affecting local carbon users (roots and soil microorganism) and carbon substrate supply in meadow steppe grasslands. The future soil carbon sequestration in the studied meadow steppe will be benefited more by the moderate grazing disturbance. [ABSTRACT FROM AUTHOR]

Aims: Disturbance regimes are changing rapidly, along with the generation of patchy habitats, and the consequences of such changes for ecosystems will be profound. Plateau zokor mounds are a common natural disturbance on the Tibetan Plateau, and this disturbance leads to bare patches, and catalyse new paradigms of plant community dynamics in alpine ecosystems. Methods: We investigated, over 6 consecutive years, the dynamic changes of new zokor mounds, the effects of different zokor mound densities on plant diversity in alpine meadows at the spatial scale, and successional shifts in plant community on the bare mound patches at the temporal scale. Results: The results showed that as the mound density increased, the species diversity and biomass of the plant communities (within mound-free regions between the mounds) significantly increased. Zokor mounds representing different successional stages comprise a mosaic and together constitute the alpine meadow. The cycle of plant succession on the bare mounds is about 6 years in length. The pioneer species were mainly rhizomatous grasses and broadleaf forbs. As succession progressed, the dominant species differed among the different mound patches. However, at the end of succession, the dominant species were grasses, and the species compositions were similar in the communities. The plant succession on the bare mound patches of the alpine meadow is a developmental process from founder-controlled to dominance-controlled communities. Conclusion: The coupling between patch-to-patch mosaic on different phases and year-to-year succession on bare mound patches is very important for species coexistence and promotes alpine meadow renewal. [ABSTRACT FROM AUTHOR]

Aims: This study investigated the influences of herbivore grazing intensity and grazing season on decomposition and nutrient release of dung and litter, which aimed to improve our understandings of grazing affecting nutrient cycling in alpine meadows on the Qinghai-Tibetan Platean. Methods: A factorial design experiment comprising 3 grazing intensities (non-grazing, moderate grazing, and heavy grazing) and 2 grazing seasons (summer and winter), was applied to quantify the decomposition and chemistry of dung and litter in an alpine pasture using the litterbag technique. Litterbags were retrieved for analysis of mass loss and nutrient release with 180, 360, 540, and 720 days after placement. Results: Grazing activity accelerated the decomposition of dung and litter and increased nutrient release from dung and litter by increasing soil temperature compared with non-grazing pastures, whereas grazing season had no effect on decomposition. The decomposition time was shorter for dung than that for litter. Conclusions: Herbivores grazing benefited dung and litter decomposition and nutrient cycling directly by increasing soil temperature, which is likely to promote soil microbial activity due to low temperatures in alpine meadows, and indirectly through herbage ingestion and dung deposition which increase the organic debris concentration used for microorganisms growth and reproduction. This study provides insights into the mechanisms of grazing regulating nutrient cycling in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Determining base cation and trace element dynamics in plant-soil systems is important for sustainable utilization of grasslands affected by global ecosystem nitrogen (N) enrichment. Methods: A 4-year field experiment was conducted with urea addition rates of 0, 2.5, 5, 7.5, 10, 15, 20, and 30 g N m−2 yr.−1 to investigate the dynamics of base cations (Ca, Mg, K) and trace elements (Fe, Mn, Cu and Zn) in soil and a dominant species Leymus chinensis in a semi-arid meadow grassland of northeast China. Results: Soil showed a significant decrease in exchangeable Ca and increases in extractable Fe, Mn and Zn concentrations, while plant Ca and Zn remained unchanged and plant Fe decreased with N addition. For both plant and soil compartments, stoichiometric ratios of trace elements were more variable than base cations, mainly driven by plant physiological requirements, plant nutrient uptake intensity, and elemental interactions. Excessive soil Mn mobilization and plant uptake affected concentrations of Fe, Cu and Zn in the plant and even inhibited Fe absorption (antagonistic interactions), resulting in a plant Fe:Mn ratio lower than 1.5 with high N addition rates, indicating Mn phytotoxicity or Fe deficiency. As a result, plant elemental stoichiometry did not remain homeostatic and was even more variable than in soil. Conclusions: Our results provided direct evidence of decoupled plant-soil elemental responses, stricter homeostatic control of macronutrients than trace elements in plants, and altered stoichiometric variability in the plant-soil system, and suggest that N addition enhances metal nutrient imbalances in the meadow steppe grassland. [ABSTRACT FROM AUTHOR]

Aims: Increasing nitrogen (N) deposition has considerable effects on soil organic matter (SOM) decomposition mediated by soil enzyme activities. Few studies, however, have explored how N addition shapes soil enzyme activity patterns by changing plants, soils and microbes. Methods: We conducted a five-year field fertilization experiment (0, 5, 10, and 15 g N m−2 yr.−1) to study how N addition affected soil enzyme activity patterns in the topsoil (0–20 cm) and subsoil (20–40 cm) in a Tibetan alpine meadow. Enzyme activity patterns were calculated by the percentage of the sum of all measured enzyme activities. The composition of the plant and microbial communities were evaluated through measuring the abundance of plant functional groups and quantifying microbial phospholipid fatty acids (PLFAs), respectively. Soil pH and available N were also measured. Results: We found that soil N availability primarily controlled plant community composition, but pH controlled the composition of the microbial community, irrespective of soil depth. Soil enzyme activity patterns differed between two soil depths and among N addition rates. Importantly, N addition shaped soil enzyme activity patterns through the changes in soil pH rather than via the composition of the plant and microbial communities. Conclusions: Our findings indicate that N addition can affect components of plant-soil system and, in particular, weaken the linkages between plant and microbial communities and enzyme activity patterns. The work suggests that N enrichment-induced soil acidification plays a key role in SOM decomposition and nutrient cycling in the Tibetan meadow ecosystem. [ABSTRACT FROM AUTHOR]

Background and aims: In recent years, ecologists have tried to determine the importance of intraspecific trait variation (ITV) versus community composition change (CCC) in shifts in community functional composition. However, results to date have not provided generality.Methods: A six-year nitrogen (N) fertilization experiment was conducted in species-rich alpine meadow communities. We focused on five key functional traits (height, leaf dry mass content LDMC, specific leaf area SLA, leaf nitrogen content LNC, and leaf phosphorus content LPC) that belong to three trait categories (whole-plant level trait, leaf morphology trait and leaf chemical trait) and measured biomass of each species in community. A sum of squares decomposition method was used to distinguish the relative contribution of ITV versus CCC to community weighted mean (CWM) traits.Results: Our results showed that N fertilization led to increasing heightCWM and LNCCWM due to light competition intensification and soil nutrient enrichment. However, the responses of community-wide SLA, LDMC and LPC were highly inconsistent and depended on the balance of different opposing processes. Moreover, during short-term fertilization, ITV played a more important role in mediating functional composition changes in all traits, but the effects of CCC overwhelmed ITV and became more important in determining community-wide whole-plant level trait and leaf morphology traits (height, LDMC and SLA) in subsequent fertilization years. On the other hand, ITV always played a more important role than CCC in determining the community-wide leaf chemical traits (LNC and LPC), but CCC had a greater contribution than ITV in terms of explaining shifts in whole-plant traits (height) and leaf morphology traits (LDMC and SLA). In addition, both positive and negative covariations appeared in our study, indicating that community-wide trait shifts due to ITV and CCC may either reinforce or oppose one another, depending on different trait categories.Conclusions: These findings highlight the importance of ITV, CCC and their covariation in mediating community functional composition, and the relative importance of ITV effects and CCC effects depended on fertilization duration and trait category. This study significantly improve our understanding of the mechanisms governing the shifts in community functional composition under N deposition scenarios. [ABSTRACT FROM AUTHOR]

Background and aims: Plant breeding usually focuses on conspicuous above-ground plant traits, yet roots fundamentally underpin plant fitness. Roots show phenotypic plasticity in response to soil conditions but it is unclear whether domesticated plants respond like their ancestors. We aimed to determine how root traits differed between ancestral and domesticated types of a meadow grass (Microlaena stipoides) under altered regimes of precipitation and soil silicon availability.Methods: We subjected the two grass types to three simulated precipitation regimes (ambient, +50%/deluge and −50%/drought) in soil with (Si+) and without (Si−) silicon supplementation and then characterised root biomass, architectural complexity and toughness in addition to shoot traits.Results: Domestication increased root tissue density, decreased specific root length (SRL) and decreased root architectural complexity. Domestication also increased root strength under Si− conditions but not Si+ conditions. Fine roots, SRL, architectural complexity and the force required to tear the roots all decreased under deluge. The ancestral and domesticated grasses responded similarly to precipitation, except that the latter had weaker roots (decreased fracture strain) under drought.Conclusions: Domestication and increased precipitation caused changes in M. stipoides root traits that could be beneficial against some stresses (e.g. soil compaction, herbivory) but not others (e.g. drought). [ABSTRACT FROM AUTHOR]

Background and aims: Soil respiration is an important component of terrestrial carbon cycling and is sensitive to environmental change. Most previous studies focus on the effect of soil temperature and moisture on soil respiration, whereas the impact of spatial heterogeneity (e.g., microtopography) is seldom studied. Methods: To test the impact of microtopography on soil respiration, we performed a field investigation to examine soil respiration, soil temperature, soil water content, soil total porosity, soil organic content, and plant biomass at a hummock site (composed of grass hummocks and inter-hummock areas) and an adjacent flat meadow of the Qinghai-Tibetan plateau. Results: Similar seasonal dynamics of soil respiration in the grass hummocks, inter-hummock areas, and flat meadow were found in the alpine meadow of the Qinghai-Tibetan plateau. However, soil respiration of the grass hummocks was 79.3% and 413.9% higher than that of the flat meadow during the growing (April, June, August) and non-growing seasons (October, December, February), respectively. Although there was no difference in soil respiration between the inter-hummock areas and the flat meadow during the non-growing season, soil respiration was 42.5% higher at the inter-hummock areas than the flat meadow during growing season. Larger soil porosity, greater surface area, and more substrate supply, but not more root growth, likely contributed to the higher soil respiration of grass hummocks. Conclusions: Our findings suggest that the impact of spatial heterogeneity on soil respiration should be taken into consideration to facilitate the accurate estimation of soil carbon fluxes at ecosystem and regional scales. [ABSTRACT FROM AUTHOR]

Background and aims: The rhizosphere priming effect is caused by root carbon (C) exudation into the rhizosphere; the role of this effect in nutrient cycling and ecosystem recovery of natural grasslands as affected by different grazing intensities is still unknown. The objective of the present study was to investigate the relationships among root C exudation, rhizospheric microbial activity, and their influences on plant nutrient uptake during grazing and recovery periods . Methods: Field experiments were conducted in the Hongyuan Alpine Meadow to measure root exudation rate and nutrient cycling processes of the dominant species Elymus nutans. Three grazing intensities (an ungrazed control, moderate grazing and heavy grazing) were introduced for two months, following which all treatments received a recovery practice (no grazing for 21 days). Results: Heavy grazing significantly decreased root exudation rate, soil nitrogen (N) mineralization rate, β-1,4-glucosidase (BG) activity, and foliar C concentration, while moderate grazing had no influence on these parameters compared to the control. After the 21 days of recovery, all these parameters, except N mineralization rate and foliar C concentrations in the heavy grazing treatment, returned to similar levels as in the control, whereas root exudation rate and BG activity rose to even higher levels. Meanwhile, moderate grazing significantly promoted root exudation rate, soil inorganic N concentration, net soil N mineralization rate, and β- N-acetylglucosaminidase (NAG) activity during the recovery stage as compared to the control. Foliar quality was also improved by the recovery practice, indicating that the high availability of N and P is a consequence of the positive root-microbe feedback and will ultimately benefit grazers. Conclusions: The flush of labile C released to the rhizosphere by grazed plants stimulated extracellular enzyme activities, enhanced soil N mineralization, and increased plant nutrient uptake. These results imply that reasonable (i.e. moderate) grazing followed by a recovery practice can effectively restore and strengthen grassland vegetation, and contribute to the sustainable use of alpine meadows such as Hongyuan. [ABSTRACT FROM AUTHOR]

Aims: A lacking of understanding about cooling effects on methane (CH) fluxes and potential asymmetrical responses to warming and cooling causes uncertainty about climate change effects on the atmospheric CH concentration. We investigated CH fluxes in an alpine meadow on the Tibetan Plateau in response to climate warming and cooling. Methods: A 2-year reciprocal translocation experiment was implemented to simulate climate warming (i.e. downward translocation) and cooling (i.e. upward translocation) along an elevation gradient with four different vegetation types (at 3200, 3400, 3600 and 3800 m elevation) during the growing season (May to October) in 2008 and 2009. Results: Although the effects of warming and cooling varied depending on vegetation type, elevation and timescale (i.e., daily and seasonally), warming increased average seasonal CH uptake by 60 %, while cooling reduced it by 19 % across all vegetation types, based on a 1.3-5.1 °C difference in soil temperature at 20 cm depth. Soil temperature over the range of 4-10 °C explained 11-25 % of the variation in average seasonal CH fluxes, while there was no relationship with soil moisture over the range of 13-39 % and soil NH-N and NON content. Methane uptake was more sensitive to warming than to cooling. Conclusions: Because of warming and cooling spells in the alpine region, warming effects on CH uptake would be over-estimated by 64 % if cooling effects on it are not considered. Our findings suggest that asymmetrical responses of CH fluxes to warming and cooling should be taken into account when evaluating the effects of climate change on CH uptake in the alpine meadow on the Tibetan plateau. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the effect of grazing season on net ecosystem CO exchange (NEE) and its components is crucial to predict the feedback of grazing management to climate change. Methods: We estimated NEE, gross primary productivity (GPP) and ecosystem respiration (Re) under different seasonal grazing practices (i.e. no-grazing (NG), warm season grazing (WG) and cold season grazing (CG)) by sheep during the growing seasons from 2008 to 2012 on the Tibetan Plateau. Results: Our results show that the impacts of seasonal grazing on daily GPP, Re and NEE in the alpine meadow ecosystem varied with sampling date and year. Compared with NG and CG, WG significantly reduced average seasonal NEE by 22.7 %, because grazing impact was exacerbated by drought in July in 2010. Soil temperature only explained 19-31 % of the variation in daily GPP, Re and NEE for all grazing treatments. The interannual variabilities of GPP, Re and NEE were mainly determined by root biomass and/or average soil temperature during the growing season. Conclusions: Our results suggest that although WG may decrease sequestration of CO under continuous drought conditions after grazing, it would have little impact on CO sequestration during the growing season under conditions of future warming with greater rainfall in alpine meadows on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Background and aims: Niche complementarity arising from divergence in resource use is an important mechanism underlying species coexistence. We hypothesized fertilization with different N forms would generate plastic divergence among species with regard to their N form uptake and preference. Methods: In the eighth year of a long-term N fertilization experiment in an alpine meadow on the Tibetan plateau, we labeled 11 common plant species with ammonium-N or nitate-N in subplots without fertilization (control) or fertilized with 7.5 g N m yr in the form of ammonium, nitrate, or ammonium nitrate to trace N form uptake. Results: Depending on species, fertilization with nitrate or ammonium nitrate had positive, negative or neutral effects on NO-N uptake rate, although ammonium fertilization showed little impact. By contrast, fertilization with any N form had little impact on NH-N uptake rate. Consequently, effects of nitrate fertilization and ammonium nitrate fertilization on relative N form preference diverged among the species and the functional groups (grasses, sedges, legumes and forbs). Conclusions: Alpine plant species can diverge in N form uptake and preference in response to long-term N fertilization, and such divergence may contribute to species coexistence after long-term fertilization. [ABSTRACT FROM AUTHOR]

Background and Aims: Numerous studies noted that the seed banks of drained former wet-meadows did not have enough residual seed potential for the successful restoration of species-rich fen-meadows. However, it is unclear whether a decline in groundwater level exerts a negative effect on the seed survival of wet-meadow plant species in the soil. This paper assessed the dependence of soil seed survival on different groundwater levels. Methods: We tested the influence of the groundwater level on the seed survival rate of 8 wet-meadow plant species in fen lysimeters with constant groundwater levels of 5, 30 and 70 cm. Seeds were buried in nylon mesh bags at 2 depths (5 and 25 cm), exhumed after 1, 3 and 5 years in the spring and tested in a climate chamber for germinable seeds under conditions of different day-night rhythms and fluctuating temperatures. Results: At both burial depths, more viable seeds survived at lower groundwater levels compared with groundwater levels near the surface. Waterlogged conditions resulted in a significant reduction in the number of germinable seeds for most of the studied plant species. A cluster analysis divided the eight plant species into three groups which differed in soil seed bank persistence and tolerance towards soil wetness. Conclusions: The decline of the groundwater level due to fen-meadow drainage does not negatively affect the seeds of wet-meadow plant species. Our results also suggest that for some species, the classification of soil seed bank type may vary according to the groundwater level dynamic of the location. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the role of resource availability in structuring biotic communities is of importance in community ecology. This study investigates how light and soil nutrient availability drive assemblages of both plants and their root-associated arbuscular mycorrhizal fungi (AMF). Methods: We conducted a 4-year light [full light or shade] and soil fertility [unfertilized or fertilized with (NH)HPO] interactive manipulations in an alpine meadow ecosystem. Species and phylogenetic compositions of plant and AMF communities were simultaneously measured, and the primary ecological processes structuring both communities were inferred from the community phylogenetic analysis. Results: Reducing light and/or increasing soil fertility significantly reduced species richness and changed community compositions of both plant and AMF. Plant community phylogenetic structure shifted from random in untreated control to overdispersion in other treatments, whereas AMF communities were phylogenetically clustered and random in unfertilized and fertilized plots, respectively. These results suggest that plant communities in treated plots were mainly determined by competitive exclusion, and that AMF communities in unfertilized and fertilized plots were determined by environmental filtering and random process, respectively. Conclusions: We observed strong effects of light and soil nutrient availability on both plant and AMF communities, and our findings highlight that the primary ecological processes that drive plant and AMF assemblages should be highly dependent on the level of resource availability. [ABSTRACT FROM AUTHOR]