Effects of nitrogen and phosphorus fertilization on soil carbon fractions in alpine meadows on the Qinghai-Tibetan Plateau

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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 (N 5 , N 10 , N 15 , P 5 , P 10 , P 15 , N 5 P 5 , N 10 P 10 , and N 15 P 15 ) 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 N 5 , N 10 , P 5 , and P 10 in 0-20 cm, and increased in N 10 and P 5 while decreased in other treatments in 20-40 cm. Most of the fertilization treatments decreased the respiratory quotient (qCO 2 ) in 0-20 cm but increased qCO 2 in 20-40 cm. Fertilization increased soil microbial functional diversity (except N 15 ) but decreased cumulative C mineralization (except in N 15 in 0-20 cm and N5 in 20-40 cm). Soil organic C (SOC) decreased in P 5 and P 15 in 0-20 cm and for most of the fertilization treatments (except N 15 P 15 ) in 20-40 cm. Overall, these results suggested that soils will not be a C sink (except N 15 P 15 ). 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. © 2014 Li et al.

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Li, J. H., Yang, Y. J., Li, B. W., Li, W. J., Wang, G., & Knops, J. M. H. (2014). Effects of nitrogen and phosphorus fertilization on soil carbon fractions in alpine meadows on the Qinghai-Tibetan Plateau. PLoS ONE, 9(7). https://doi.org/10.1371/journal.pone.0103266

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