Different effects of sheep excrement type and supply level on plant and soil C:N:P stoichiometry in a typical steppe on the loess plateau

摘要

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.