Divergent responses of soil bacterial and fungal biomass carbon and phosphorus (P) to a P addition gradient

Abstract

Microorganisms mediate element dynamics in soils through biomass turnover, and their activity is largely affected by nutrient inputs. However, as the two major subgroups of soil microbial community, little is known regarding how bacterial and fungal biomass carbon (C) and phosphorus (P) respond to a P addition gradient. Herein, the dynamic changes of bacterial and fungal biomass C and P from the soil in northern China were studied using the selective inhibition technique. A 20-d soil incubation experiment was set up with different P additions: 0, 20 and 60 mg kg⁻¹ soil. The experiment selected streptomycin (10 mg g⁻¹ soil) and cycloheximide (20 mg g⁻¹ soil) as bacterial and fungal inhibitors, respectively. The results showed that P addition did not affect the total microbial biomass C but substantially adjusted the composition contributed by bacteria and fungi. Fungal biomass C contributed highest at the low P addition rate, but its significance tended to decrease as P addition increased, whereas the contribution of bacterial biomass C increased. P addition positively affected both bacterial and fungal biomass P, but at a higher extent for bacteria. In terms of time, bacteria showed a higher potential to release P into soil labile P pools through biomass turnover at an earlier stage after P addition, whereas fungi may have a slow effect as sources of soil labile P. These results indicate divergent responses for bacterial and fungal biomass across different P additions. Such insights should be considered at field scale and should inform C and nutrient managements planning in terms of soil C and P cycling.