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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]

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: 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]

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: 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: To assess the effects of atmospheric N deposition on the C budget of an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, it is necessary to explore the responses of soil-atmosphere carbon dioxide (CO) exchange to N addition. Methods: Based on a multi-form, low-level N addition experiment, soil CO effluxes were monitored weekly using the static chamber and gas chromatograph technique. Soil variables and aboveground biomass were measured monthly to examine the key driving factors of soil CO efflux. Results: The results showed that low-level N input tended to decrease soil moisture, whereas medium-level N input maintained soil moisture. Three-year N additions slightly increased soil inorganic N pools, especially the soil NH-N pool. N applications significantly increased aboveground biomass and soil CO efflux; moreover, this effect was more significant from NH-N than from NO-N fertilizer. In addition, the soil CO efflux was mainly driven by soil temperature, followed by aboveground biomass and NH-N pool. Conclusions: These results suggest that chronic atmospheric N deposition will stimulate soil CO efflux in the alpine meadow on the Qinghai-Tibetan Plateau by increasing available N content and promoting plant growth. [ABSTRACT FROM AUTHOR]