Soil aggregation is a key ecosystem process, especially in arid and semi-arid grassland ecosystem. Ungulates influence soil aggregate stability in conflicting ways, for example, removing biomass by browsing and improving plant growth by excreta deposition to alter plant induced binding agents into soil. Therefore, this outcome is difficult to predict because the magnitude and direction of grazing components and their interaction (defoliation, trampling and dung and urine return) and the response of each individual property from plant and soil and its contribution to soil stability varies. A manipulative experiment with eight treatments and eight replicates was conducted in a semi-arid grassland in Inner Mongolia, China, to investigate the relative role of grazing components on soil aggregates and stability. We assessed the effects of defoliation (mowing), trampling and dung and urine return (mixture of dung and urine addition) and their combinations on the changes in plant attributes, soil properties and soil fungal community that concern soil aggregate stability through a 3-years simulated grazing experiment.
Results/Conclusions
Surprisingly, defoliation, but not trampling, had a strong effect and disintegrated macroaggregates and in turn reduced aggregate stability. Although trampling and defoliation significantly increased soil bulk density, trampling did not decrease soil aggregate stability, even rescue the negative effects in the presence of defoliation (mowing × trampling, P﹤0.05). Soil aggregation and its stability were pronounced correlations with soil fungal community composition. Defoliation significantly altered plant functional community, and it was strongly correlated with soil fungal community composition. Furthermore, the application of dung and urine improved soil nutrient availability (e.g. soil N), in combination with its altered soil fungal community, was benefit to aggregate stability.Our results demonstrated that the importance of defoliation induced indirect effects on soil fungi via changes in plant community in dictating soil aggregates’ responses to grazing. Our results further show that trampling and dung and urine return are essential for soil aggregates cope with a high pressure of plant removal. Grazing management strategy needs to be explore the function of soil fungal community and diversity and its correlated soil aggregate stability, is a key aspect for soil conservation, grassland restoration and erosion prevention from grazing disturbance.