| In recent years, ecological stoichiometry has been an emerging field of ecology. It makes different levels of biology (molecular, cellular, organism, population, ecological system and global scale) organically combined, and is also widely used in ecological research. The effects of large herbivores grazing on grassland plant diversity have been considered as an important scientific issue in grassland ecology. In this paper, we studied the influence of different grazing modes on plant and soil C:N:P ecological stoichiometry under different plant diversity. It improved our understanding for the mechanisms of grazing impacts on plant diversity, and also has an important theoretical and practical significance for managing grazing herbivore, promoting the development of animal husbandry, restoring and maintaining biological diversity, and protecting grassland ecosystem service functions.In this experiment, we studied the effects of different grazing (cattle grazing alone, sheep grazing alone and mixed grazing of cattle and sheep) on plant and soil C:N:P ecological stoichiometry in Songnen grassland under high and low plant diversity. The results are as follows:(1) At low plant diversity, different grazing modes significantly decreased C:N and C:P of Poaceae (Calamagrostis epigeios excluded) and Compositae. But there were not significant differences in the C:N of Poaceae, C:N and C:P of Compositae among different grazing treatments. Compared with cattle or sheep grazing alone, mixed grazing of cattle and sheep significantly increased C:P of Poaceae. The C:P of Leymus chinensis and Phragmites australis when grazing cattle alone were significantly higher than when grazing sheep alone and mixed grazing. Grazing significantly reduced the N:P of Compositae-Artemisia anethifolia.(2) At high plant diversity, the different grazing significantly reduced C:N of Poaceae. The effects of sheep grazing alone on C:N of Poaceae was greater than that cattle grazing alone and mixed grazing of cattle and sheep. Different grazing modes had no consistent effect on C:P of Poaceae, C:N and C:P of Compositae. Sheep grazing alone and mixed grazing significantly reduced the C:P of Calamagrostis epigeios, but had no significantly effects on the other Poaceae plant species. Grazing significantly reduced C:N and C:P of Artemisia scoparia and Artemisia anethifolia, but had no significantly effects on Kalimeris integrifolia. Grazing increased N:P of Leymus chinensis and Puccinellia tenuiflora, but had no significantly effects on Phragmites australis and Calamagrostis epigeios.(3) At the plant community level, different grazing on plant C:N:P characteristics of ecological stoichiometry were also different under plant diversity. At low plant diversity, cattle grazing alone and mixed grazing of cattle and sheep significantly reduced C:N and C:P of plant. The sheep grazing alone significantly increased C:P of plant, while C:N:P of plant were most significantly changed under cattle grazing alone. At high diversity, grazing significantly reduced C:N, but increased N:P, and no significant effects for C:P.(4) At different plant diversity, the effects of grazing on the soils were also different. At low plant diversity, cattle grazing alone and mixed grazing significantly increased P content of shallow soil (0-15 cm), while C:N, C:P and N:P were significantly reduced. Short-term grazing had no significantly effects on C:N:P ecological stoichiometry of 15-30 cm soil, but the significant effects could be seen in further study.In summary, the effects of grazing on C:N:P ecological stoichiometry characteristics of plant and soil were different at different plant diversity. Increasing plant diversity reduced the effects of cattle on plant C:N:P, but strengthened the role of sheep. Mixed grazing of sheep and cattle had different compensation effects on the plant at low plant diversity. Grazing affected C:N:P ecological stoichiometry of shallow soil (0-15 cm). Increasing plant diversity decreased the effect of grazing on the 0-15 cm soil. |
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