title: Effects of nitrogen and phosphorus fertilization on soil carbon fractions in alpine meadows on the Qinghai-Tibetan Plateau.
abstract: In grassland ecosystems, N and P fertilization often increase plant productivity, but there is no concensus if fertilization affects soil C fractions. We tested effects of N, P and N+P fertilization at 5, 10, 15 g m-2 yr-1 (N5, N10, N15, P5, P10, P15, N5P5, N10P10, and N15P15) compared to unfertilized control on soil C, soil microbial biomass and functional diversity at the 0-20 cm and 20-40 cm depth in an alpine meadow after 5 years of continuous fertilization. Fertilization increased total aboveground biomass of community and grass but decreased legume and forb biomass compared to no fertilization. All fertilization treatments decreased the C:N ratios of legumes and roots compared to control, however fertilization at rates of 5 and 15 g m-2 yr-1 decreased the C:N ratios of the grasses. Compared to the control, soil microbial biomass C increased in N5, N10, P5, and P10 in 0-20 cm, and increased in N10 and P5 while decreased in other treatments in 20-40 cm. Most of the fertilization treatments decreased the respiratory quotient (qCO2) in 0-20 cm but increased qCO2 in 20-40 cm. Fertilization increased soil microbial functional diversity (except N15) but decreased cumulative C mineralization (except in N15 in 0-20 cm and N5 in 20-40 cm). Soil organic C (SOC) decreased in P5 and P15 in 0-20 cm and for most of the fertilization treatments (except N15P15) in 20-40 cm. Overall, these results suggested that soils will not be a C sink (except N15P15). Nitrogen and phosphorus fertilization may lower the SOC pool by altering the plant biomass composition, especially the C:N ratios of different plant functional groups, and modifying C substrate utilization patterns of soil microbial communities. The N+P fertilization at 15 g m-2 yr-1 may be used in increasing plant aboveground biomass and soil C accumulation under these meadows.
authors: State Key Laboratory of Grassland Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, P.R. China.
authors: Jin Hua
authors: JH
authors: Li
authors: State Key Laboratory of Grassland Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, P.R. China.
authors: Yu Jie
authors: YJ
authors: Yang
authors: State Key Laboratory of Grassland Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, P.R. China.
authors: Bo Wen
authors: BW
authors: Li
authors: State Key Laboratory of Grassland Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, P.R. China.
authors: Wen Jin
authors: WJ
authors: Li
authors: State Key Laboratory of Grassland Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, P.R. China.
authors: Gang
authors: G
authors: Wang
authors: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America.
authors: Johannes M H
authors: JM
authors: Knops
mesh_terms: D018533:Biomass; D002244:Carbon / Q000737:chemistry*; D017753:Ecosystem; D065948:Grassland; D009584:Nitrogen / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D010944:Plants; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D018609:Tibet
chemical_list: D012987:Soil; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen