Associations of soil bacterial and fungal gene abundances with potential microbial respiration and metabolic quotient across grasslands of the eastern Loess Plateau

Abstract Background Soil microbial respiration (SMR) and microbial metabolic quotient (MMQ) are key parameters for understanding the microbial regulation of the carbon (C) dynamics. The changes and associated factors of SMR and MMQ across different grazing intensities and grassland types at the regional scale remain unclear. Methods This study selected 42 grassland sites across the eastern Loess Plateau, representing a gradient of grazing intensities (ungrazed, light grazing, moderate grazing, and heavy grazing) and encompassing multiple grassland types (mountain steppe, subalpine meadow, and warm shrubby tussock), to measure SMR, MMQ, as well as soil bacterial 16S rRNA gene and fungal ITS gene abundances. Results Different grassland types exhibit varying SMR, rather than MMQ; and the SMR of subalpine meadow is significantly higher than that of mountain steppe and warm shrubby tussock. Grazing disturbance did not significantly affect SMR, while MMQ showed a trend of first increasing and then decreasing with increasing grazing intensity. Different grazing intensities had no significant effect on soil bacterial and fungal abundance; however, bacterial 16S rRNA gene and fungal ITS gene abundances in the subalpine meadow were significantly higher than those in the mountain steppe and the warm shrubby tussock. Regression analysis showed that SMR was significantly positively correlated with altitude, bacterial 16S rRNA gene and fungal ITS gene abundances; MMQ was significantly negatively correlated with altitude and bacterial 16S rRNAgene abundances. Results of variation partitioning analysis (VPA) and redundancy analysis (RDA) indicate that SMR and MMQ have stronger associations with soil bacterial 16S rRNA gene and fungal ITS gene abundances than with grazing disturbance, grassland type, climatic and geographical factors. Conclusions The variations in SMR and MMQ were closely associated with bacterial 16S rRNA gene and fungal ITS gene abundances at the regional scale across the grasslands of the eastern Loess Plateau.