Grazing directly or indirectly affect shoot and root litter decomposition in different decomposition stage by changing soil properties

Abstract Grazing can affect the grassland microclimate, soil properties, and litter quality, thereby affecting litter decomposition. However, it is still unclear which grazing intensity provides the most suitable environment for litter decomposition, and which factors play the dominant role in shoot and root litter decomposition. To investigate the effect of grazing on shoot and root litter decomposition, and the dominant factors in each decomposition period, we conducted a 17-month (from May 2016 to September 2017) litter bag experiment under five grazing intensities (control, light grazing, medium grazing, heavy grazing, and extremely heavy grazing, based on local grazing pressure standard) in a temperate grassland in Inner Mongolia, China. We divided the litter decomposition process into three stages according to the seasons. In the first growing season, the decomposition rate of shoot litter was faster under light grazing, probably because better soil environment was beneficial for microbes, and the high precipitation promoted leaching loss of soluble components. In the non-growing season, snow cover played an important role in litter decomposition. In the second growing season, the accumulation of macroelements (nitrogen, N; phosphorus, P) and microelements (magnesium, Mg; manganese, Mn) accelerated litter decomposition. Heavy and extremely heavy grazing intensities promoted the breakdown of cellulose in shoot litter. Medium grazing intensity could promote refractory substances decomposition in root litter. But the mass loss rate of root litter was inhibited by grazing, which was regulated by MBC/MBN. Our results indicate that different grazing intensities had different effects on the decomposition of shoot and root litter. At each stage of decomposition, the dominant factors of shoot and root litter decomposition were different and directly or indirectly affected by grazing and season.