title: Soil resource availability impacts microbial response to organic carbon and inorganic nitrogen inputs.
abstract: Impacts of newly added organic carbon(C) and inorganic nitrogen (N) on the microbial utilization of soil organic matter are important in determining the future C balance of terrestrial ecosystems. We examined microbial responses to cellulose and ammonium nitrate additions in three soils with very different C and N availability. These soils included an organic soil (14.2% total organic C, with extremely high extractable N and low labile C), a forest soil (4.7% total organic C, with high labile C and extremely low extractable N), and a grassland soil (1.6% total organic C, with low extractable N and labile C). While cellulose addition alone significantly enhanced microbial respiration and biomass C and N in the organic and grassland soils, it accelerated only the microbial respiration in the highly-N limited forest soil. These results indicated that when N was not limited, C addition enhanced soil respiration by stimulating both microbial growth and their metabolic activity. New C inputs lead to elevated C release in all three soils, and the magnitude of the enhancement was higher in the organic and grassland soils than the forest soil. The addition of cellulose plus N to the forest and grassland soils initially increased the microbial biomass and respiration rates, but decreased the rates as time progressed. Compared to cellulose addition alone, cellulose plus N additions increased the total C-released in the grassland soil, but not in the forest soil. The enhancement of total C-released induced by C and N addition was less than 50% of the added-C in the forest soil after 96 d of incubation, in contrast to 87.5% and 89.0% in the organic and grassland soils. These results indicate that indigenous soil C and N availability substantially impacts the allocation of organic C for microbial biomass growth and/or respiration, potentially regulating the turnover rates of the new organic C inputs.
authors.affiliation: Department of Agronomy, Nanjing Agricultural University, Nanjing 210095, China. zwj@njau.edu.cn
authors.forename: Wei-Jian
authors.initials: WJ
authors.lastname: Zhang
authors.forename: W
authors.initials: W
authors.lastname: Zhu
authors.forename: S
authors.initials: S
authors.lastname: Hu
mesh_terms: D000704:Analysis of Variance; D018533:Biomass; D002244:Carbon / Q000032:analysis*; D002482:Cellulose / Q000378:metabolism; D017753:Ecosystem; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis*; D009657:North Carolina; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology
chemical_list: D009566:Nitrates; D012987:Soil; D002244:Carbon; D002482:Cellulose; D009584:Nitrogen; C006568:ammonium nitrate