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Aims Deposition of urine and dung is a key mechanism by which herbivores influence the nutrient cycling of terrestrial ecosystems. Yet, little is known about the roles of urine, dung and their mixtures in regulating the plant and soil carbon:nitrogen:phosphorus (C:N:P) stoichiometry and their interactions. Methods We explored how different excrement types (urine, dung and their mixtures) and supply levels [urine: 0.5, 1.0 and 1.5 L m −2 ; dung: 4.7, 9.4 and 14.2 g m −2 ; mixtures (urine+dung): 0.5 + 4.7, 1.0 + 9.4 and 1.5 + 14.2] altered the plant and soil C:N:P stoichiometry in a semi-arid grassland on the Loess Plateau. Results We found that the aboveground biomass of the whole community was highest at the highest mixtures application rate, while the highest aboveground biomass of the three dominant species was detected at applications of 0.5 L m −2 urine for Stipa bungeana , 9.4 g m −2 dung for Lespedeza davurica and 1.0 L m −2 urine +9.4 g m −2 dung for Artemisia capillaris . Urine and dung alone increased plant N concentration, which peaked at 1.0 L m −2 urine. Plant P concentration at 1.5 + 14.2 mixtures was significantly higher than that at control without significant difference between excrement types. Compared to the control, excrement deposition did not significantly change plant C concentration and C:N, C:P and N:P ratios. However, plant C:P and N:P ratios under the mixtures were significantly lower than those under urine or dung. Excrement applications led to more soil (total, microbial and organic) C, N and P accumulations. Compared to urine and dung, the mixtures induced higher total P concentration but lower total N concentration in soil. Conclusions Our study demonstrated that the impacts of sheep urine and dung on plant and soil C and nutrient concentrations and stoichiometry differed from that of mixtures. The plant N:P ratio indicated balanced N:P supply for urine and dung applications but N limitation for mixtures application. This study provides experimental evidence that the excrement of herbivores plays an important role in altering ecological stoichiometry in plants and soil.

s Background Sand burial and precipitation drive the community structure and function of semi-arid grassland. Stipa bungeana is a tillerous clonal plant that often forms a community in the sandy grassland, however, it is not clear how sand burial, precipitation enhancement and their interaction on importance of S. bungeana in the plant community. In the semi-arid desertification grassland in northern China, we conducted a two-years field experiment with simulated sand burial (no sand burial, 2 cm and 5 cm sand burial) and precipitation enhancement (ambient precipitation, 1/7 and 2/7 precipitation enhancement) treatments, and the morphological characteristics and important value of S. bungeana were determined. Results Sand burial and precipitation enhancement promoted the growth of S. bungeana tillers, but reduced the size and aboveground biomass of S. bungeana tuft, thus affecting the status of S. bungeana in the community. Sand burial and precipitation enhancement also significantly reduced plant density and aboveground biomass of all other species except S. bungeana . Conclusions These results revealed that S. bungeana may lose its status as the constructive species, due to the accumulation of the negative effects of sand burial. Our findings may be helpful to better understand the process of desertification, and will contribute to grassland management and vegetation restoration in semi-arid desert areas.

Caragana korshinskii, a leguminous shrub, a common specie, is widely planted to prevent soil erosion on the Loess Plateau. The objective of this study was to determine how the plantation ages affected soil, leaf and root nutrients and ecological stoichiometry. The chronosequence ages of C. korshinskii plantations selected for this study were 10, 20 and 30 years. Soil organic carbon (SOC) and soil total nitrogen (STN) of C. korshinskii plantations significantly increased with increase in the chronosequence age. However, soil total phosphorous (STP) was not affected by the chronosequence age. The soil C: N ratio decreased and the soil C: P and N: P ratios increased with increasing plantation age. The leaf and root concentrations of C, N, and P increased and the ratios C: N, C: P, and N: P decreased with age increase. Leaf N: P ratios were >20, indicating that P was the main factor limiting the growth of C. korshinskii. This study also demonstrated that the regeneration of natural grassland (NG) effectively preserved and enhanced soil nutrient contents. Compared with NG, shrub lands (C. korshinskii) had much lower soil nutrient concentrations, especially for long (>20 years) chronosequence age. Thus, the regeneration of natural grassland is an ecologically beneficial practice for the recovery of degraded soils in this area.

Aims Plant-soil feedbacks (PSFs) and grazing drive community dynamics in grasslands. We examined how the intensity of grazing and PSF interact to affect plant growth and explored what drives the observed feedback effects. Methods Three dominant perennial plant species; Arte misia capillaris, Lespedeza davurica, and Stipa bungeana were grown in field-conditioned soil (sterilized or unsterilized) collected from four grazing intensities in a semiarid grassland of northwest China. Soil nutrient concentrations and root fungal communities were determined. Results Plant biomass increased with grazing intensity for the three plant species. Within each grazing intensity, plant growth in sterilized soil relative to unsterilized soil differed markedly among species. Soil inorganic nitrogen (N) concentration tended to increase with increasing grazing intensity. Arbuscular mycorrhizal fungi (AMF) colonization was high for all grazing intensities for L. davurica. Fusarium tricinctum, the most common pathogenic Fusarium species, had the highest frequency from the control for A. capillaris and tended to increase with increasing grazing intensity for S. bungeana. Conclusions Our results suggest that in grasslands plant growth can be modified by the intensity of grazing via grazing-induced changes in soil nutrient availability and fungal communities. Additional studies are needed to determine how grazing intensity affects species coexistence through PSFs to mixed communities.

Satellite-borne multispectral data are suitable for regional-scale grassland community classification owing to comprehensive coverage. However, the spectral similarity of different communities makes it challenging to distinguish them based on a single multispectral data. To address this issue, we proposed a support vector machine (SVM)–based method integrating multispectral data, two-band enhanced vegetation index (EVI2) time-series, and phenological features extracted from Chinese GaoFen (GF)-1/6 satellite with (16 m) spatial and (2 d) temporal resolution. To obtain cloud-free images, the Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM) algorithm was employed in this study. By using the algorithm on the coarse cloudless images at the same or similar time as the fine images with cloud cover, the cloudless fine images were obtained, and the cloudless EVI2 time-series and phenological features were generated. The developed method was applied to identify grassland communities in Ordos, China. The results show that the Caragana pumila Pojark, Caragana davazamcii Sanchir and Salix schwerinii E. L. Wolf grassland, the Potaninia mongolica Maxim, Ammopiptanthus mongolicus S. H. Cheng and Tetraena mongolica Maxim grassland, the Caryopteris mongholica Bunge and Artemisia ordosica Krasch grassland, the Calligonum mongolicum Turcz grassland, and the Stipa breviflora Griseb and Stipa bungeana Trin grassland are distinguished with an overall accuracy of 87.25%. The results highlight that, compared to multispectral data only, the addition of EVI2 time-series and phenological features improves the classification accuracy by 9.63% and 14.7%, respectively, and even by 27.36% when these two features are combined together, and indicate the advantage of the fine images in this study, compared to 500 m moderate-resolution imaging spectroradiometer (MODIS) data, which are commonly used for grassland classification at regional scale, while using 16 m GF data suggests a 23.96% increase in classification accuracy with the same extracted features. This study indicates that the proposed method is suitable for regional-scale grassland community classification.

PurposeTo control the severe soil and water losses on the Loess Plateau, China, a series of vegetation restoration projects were conducted. A better understanding of the effect of vegetation types on the soil infiltration capacity is important for the sustainable development of vegetation restoration. The aim of this study was to establish a soil infiltration capacity index (SIC) and to analyze the mechanism influencing variations in the soil infiltration capacity after vegetation restoration on the Loess Plateau.Materials and methodsEight vegetation types (community dominated by Artemisia scoparia, Stipa bungeana, Artemisia gmelinii + S. bungeana, A. gmelinii + Stipa grandis, A. gmelinii + Artemisia giraldii, Sophora viciifolia, Caragana korshinskii, and Robinia pseudoacacia) and bare land as the control were selected for this study. The SIC was established by a steady infiltration rate (SR, 50–60 min) and stage I average infiltration rate (ARSI, 0–5 min) according to principal component analysis (PCA). Path analysis was used to investigate how the soil properties and plant fine root affected the soil infiltration capacity.Results and discussionThe SIC values of the eight vegetation types were all higher than that of the bare land. The R. pseudoacacia community had the highest SIC value (0.43), followed by the A. scoparia community (0.30) while the bare land (− 0.56) had the lowest value. Path analysis showed that the increase in the fractal dimension and non-capillary porosity of soil particles enhanced the SIC directly. Increases in the clay content increased the SIC by affecting the fractal dimension of soil particles, while increases in the fine root density reduced the SIC by affecting the non-capillary porosity. Plant functional groups (grasses and legumes) affected SIC indirectly via non-capillary porosity and plant root.ConclusionsA comprehensive index, the SIC, was established to describe the soil infiltration capacity by the PCA method. Based on a comparison with bare land, vegetation restoration enhanced the soil infiltration capacity. The R. pseudoacacia community was the most effective at improving the soil infiltration capacity. The improvement in infiltration was closely related to direct increases in the soil non-capillary porosity and soil particle fractal dimension.

Previous pasture residues can inhibit the establishment of exotic introduced plant species by exerting allelopathic effects. Concerning this issue, present research work was conducted to investigate the allelopathic potential of dominant native grass species ( Lespedeza davurica, Stipa bungeana, and Artemisia capillaris ) on the seed germination and seedling growth of exotic plant species (alfalfa and wheat). Different concentrations (2.5%, 5%, and 10%) of residue extracts of native grass species were used in the experiment. Results indicated that the aqueous extracts of A. capillaris and S. bungeana at all concentrations significantly suppressed the seed imbibition, germination potential, germination rate, germination index, seedling height, above and belowground biomass of alfalfa seedlings. Meanwhile, L. davurica did not show any effect on germination indexes but it significantly suppressed the seedling height of alfalfa after two weeks. However, it improved the seed imbibition, seedling height, and biomass of wheat seedlings. The greatest inhibition effect was perceived by A. capillaris followed by S. bungeana extracts. To achieve sustainable agricultural development, it is important to utilize cultivation systems that take advantage of the stimulatory and inhibitory effects of allopathic plants to regulate plant growth and development and to minimize the risk of toxicity caused by allopathic plants species. Graphical Abstract Overall processes of allelopathy and how allelochemicals are derived from the aerial parts of plants and reveals that allelochemical compounds primarily contain phenolic compounds, terpenes, and fatty acids, which influence the seed germination, survival, growth, and development of other plants (e.g., crops or weeds).

Knowledge of the germination behavior of different populations of a species can be useful in the selection of appropriate seed sources for restoration. The aim of this study was to test the effect of seed population, collection year, after-ripening and incubation conditions on seed dormancy and germination of Stipa bungeana , a perennial grass used for revegetation of degraded grasslands on the Loess Plateau, China. Fresh S. bungeana seeds were collected from eight locally-adapted populations in 2015 and 2016. Dormancy and germination characteristics of fresh and 6-month-old dry-stored seeds were determined by incubating them over a range of alternating temperature regimes in light. Effect of water stress on germination was tested for fresh and 6-month-old dry-stored seeds. Seed dormancy and germination of S. bungeana differed with population and collection year. Six months of dry storage broke seed dormancy, broadened the temperature range for germination and increased among-population differences in germination percentage. The rank order of germination was not consistent in all germination tests, and it varied among populations. Thus, studies on comparing seed dormancy and germination among populations must consider year of collection, seed dormancy states and germination test conditions when selecting seeds for grassland restoration and management.

Soil carbon and nitrogen pools are crucial for maintaining the balance of carbon and nitrogen cycling in ecosystems and also for reducing the impacts of global climate change. However, current research lacks an understanding of the effects of long-term vegetation restoration on soil carbon and nitrogen pools and their storage in vulnerable ecosystems. Therefore, we studied the characteristics of soil carbon (soil organic carbon, microbial biomass carbon, dissolved organic carbon) and nitrogen pools (total nitrogen, ammonium nitrogen, nitrate nitrogen) and their storage under four types of vegetation restoration (Stipa bungeana Trin., SB; Caragana korshinskii Kom., CK; Xanthoceras sorbifolia Bunge., XS; Picea asperata Mast., PA) in the Longzhong Loess Plateau area. We found that the carbon and nitrogen pools in the 0–40 cm soil layer under the XS and PA vegetation restoration types were higher compared to those under the SB and CK vegetation, and the values of soil ammonium–nitrogen ratios ranged from 0.72 to 0.83 under different vegetation types. Carbon and nitrogen interactions were stronger in the 0–40 cm soil under PA vegetation, which had significantly higher soil carbon (49.06 t·ha−1) and nitrogen (1.78 t·ha−1) storage than did the other vegetation types. We also found that soil carbon and nitrogen stores differed among different types of vegetation restoration. These elements were mainly distributed in soils from 0 to 20 cm depth, where the carbon and nitrogen pools in soils from 0 to 10 cm exceeded those in the lower layers. Furthermore, we discovered that redundancy analysis (RDA) supported by soil enzyme activity and physical properties significantly explained the variation in soil carbon and nitrogen triggered by vegetation restoration. According to this research, the stability and transformation of soil carbon and nitrogen pools in the region can be influenced by various forms of vegetation restoration. Additionally, the findings highlight that forest vegetation restoration can be a successful strategy for effectively sequestering soil carbon and nitrogen within the Longzhong Loess Plateau area.

Aims Soil fungal pathogens can result in the failure of seedling establishment, but the effects of fungicide applications on seed/seedling survival have differed among studies. We assumed that the variation may relate to seed dormancy/germination characteristics and hypothesized that nondormant germinating seeds are more likely to be killed by fungal pathogens than dormant seeds. Methods Dormant and nondormant seeds of Stipa bungeana and Lespedeza davurica were inoculated with a pathogenic fungus Fusarium tricinctum under laboratory and field conditions. The outcomes of seed/seedling fate and other parameters were evaluated. Results In the laboratory, nondormant seeds inoculated with F. tricinctum developed white tufts of mycelium on the radicles of germinating seeds causing them to quickly die, but dormant seeds remained intact. In contrast, in the field inoculation with F. tricinctum did not cause higher mortality of nondormant than dormant seeds but resulted in higher percentages of seedling death before they emerged from soil than the controls. Conclusions Our results suggest that dormancy protects seeds from being attacked by some pathogens by preventing germination, but the protection is lost once germination has commenced. Further study involving various plant species with more seeds is needed to assess the generality of this pathogen-seed interaction hypothesis.