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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. 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. 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. 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.

Aims Grazing is a key driver of plant communities and soil functions in grassland ecosystems. Soil nematodes play a vital role in soil ecological functions. however, few studies have explored how grazing shapes soil nematode community in different soil layers.Methods we investigated the composition, abundance, diversity, metabolic footprint, and food web metrics of soil nematodes over a gradient of grazing in the 0-10 cm and 10-20 cm soil layers in a meadow steppe. The relationships between nematode community structure and biotic and abiotic factors were analyzed by principal component analysis (PCA) and structural equation model (SEM) analysis. Results Light grazing tended to increase the abundance of soil nematodes. Intensive grazing decreased the biomass carbon and metabolic footprints of plant parasites, fungivores, and total soil nematodes in 0-10 cm soils. There was no difference in the biomass carbon and metabolic footprints of soil nematodes among different grazing intensities in the 10-20 cm soil layer. Soil moisture, aboveground biomass, belowground biomass and Shannon diversity of grass contributed more to changes in soil nematode composition in both soil layers. In the 0-10 cm soil layer, grazing directly and indirectly affected soil nematode diversity via soil moisture and aboveground biomass, while grazing directly affected soil nematode diversity in 10-20 cm soil layer. Conclusions Our results indicate that soil depth can weaken the effect of grazing intensities on soil nematode fauna. Grazing affected the soil nematode community structure via different paths in different soil layers.

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. 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. 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. 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.

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. 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). 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. 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.

Woody plant encroachment is a phenomenon of global concern in drylands due to demonstrated reductions in livestock carrying capacity. However, shrubs are known to contribute to the development of patches of enhanced fertility that might offset any negative effects of increasing grazing. We measured soil physical and chemical characteristics within shrub and open patches across a gradient in livestock grazing to explore how the relative effect of shrubs might change with increasing grazing-induced disturbance. Soil carbon, nitrogen phosphorus and bulk density were measured within 92 shrub patches and their paired interspaces at five sites ranging from long-grazed to long-ungrazed in a semiarid grassland encroached by the N-fixing shrub Caragana microphylla. We used a combination of linear and structural equation modelling to test whether shrubs might buffer any negative effects of overgrazing on soils. Shrub soils were more porous, and had more organic carbon, nitrogen and phosphorus than interspace soils. Within both microsites, however, soil bulk density increased, and soil organic carbon and nutrients declined, with increasing grazing intensity. Grazing reduced interspace plant cover and height and exacerbated the negative effects of bulk density on soil carbon, whereas shrubs had the opposite effect. The relative importance of shrubs for soil carbon and nutrients increased with increasing grazing intensity but collapsed under extreme overgrazing. These findings highlight the effect of grazing in promoting shrub dominance, which can also prevent grassland degradation. However, any positive effects of grazing collapsed when sites were severely overgrazed.

The development of fertile patches within an infertile matrix is a common phenomenon in drylands. Shrub-centered expansion of fertile islands is generally attributed to processes of sediment erosion and deposition, but there have been fewer studies of how litter might contribute to the development of fertile islands in semiarid shrub grassland. We quantified the capture of two tumble plant species (Cleistogenes squarrosa, Salsola collina; also known as tumble weeds) by shrubs across ten sites across 38,000 km2 of a semiarid grassland encroached by Caragana microphylla. Tumble plants are plants that blow across the grassland propelled by strong winds. Both tumble plant species were found over extensive areas of semiarid grassland, and their distribution coincides with the distribution of Caragana microphylla. Biomass production of both tumble plants averaged 12.2 g m−2 (range: 1.0 to 25.0 g m−2) and litter accumulation (amount accruing from wind-blown plants) of both tumble plants was significantly greater beneath shrubs (94.5 ± 28.9 g m−2 mean ± SE) than in the interspaces (3.3 ± 1.4 g m−2). Most of the material collecting under Caragana microphylla comprised tumble plants. Increases in the area of Caragana microphylla patches did not correspond to greater tumble plant capture. However, the supply of tumble plants was the strongest predictor of capture within shrub hummocks, suggesting that tumble plant capture is source limited rather than sink limited. Our structural equation model indicates that increases in grass cover and height were indirectly and negatively associated with tumble plant capture by reducing the tumble plant supply. Contrary to prediction, shrub height and shrub patch area had no overall effect on the tumble plant capture. Overall, we maintain that the capture of tumble plants by shrubs is an important self-maintaining mechanism of shrub-encroached grasslands. Tumble plant abundance is predicted to increase with increasing surface human disturbance and aridity. Therefore, the “shrub-litter island” effect is likely to be an important mechanism for maintaining and promoting the encroachment of shrubs into semiarid grasslands.

Many studies reported the influence of wind erosion on soil degradation and the effect of vegetation coverage on preventing wind erosion. However, fewer studies have quantitatively measured the grassland soil particle size fractions and nutrients’ loss caused by wind erosion under different vegetation coverage. Aims: We conducted a field experiments to (1) to explore the effect of vegetation coverage on soil wind erosion; (2) examine quantitatively the effects of wind erosion on soil texture, and determine the most erodible particles fraction of soil; (3) to examine quantitatively the soil carbon, nutrients such as nitrogen and phosphorus loss caused by wind erosion under different vegetation coverage. Methods: Six vegetation coverage treatments (0 %, 15 %, 35 %, 55 %, 75 % and 95 %) were constructed. To be able to monitor wind erosion status under more diverse weather conditions, three consecutive repeat experiments under different weather condition were conducted. Results: The results show that all the residue soil samples after wind erosion became coarser than that of original soil samples. The degree of change for the soil particle size distribution before and after wind erosion gradually increased with the less of vegetation coverage. The critical particle size for distinguishing the original soil sample and the residue soil after wind erosion occurred in the range of 125 μm and 210 μm depending on the vegetation cover. The fractions below or above the critical particle size are either easy to deplete or favoured by wind erosion, respectively. The most reduction occurs between 50 and 90 μm depending on the different weather condition and vegetation coverage. Due to the disproportionately greater amounts of nutrients in the fine soil particles, the preferential depletion of fine particles directly lead to a preferentially significant depletion of organic carbon and nutrients. The organic carbon and nutrient contents in the residue soil after erosion decreased significantly compared to that in the original soil. The soil nutrient loss ratio decrease significantly with the increase of vegetation coverage. Conclusions: Wind erosion is an important factor to affect the evolution of soil texture and soil nutrient. Vegetation coverage has a major impact on both preventing wind erosion and decreasing loss ratio of fine particles and nutrients. If we want to effectively protect the fine particles and nutrients, the vegetation cover should be maintained at least above 35 %.