Nitrogen and phosphorus enrichment accelerates soil organic carbon loss in alpine grassland on the Qinghai-Tibetan Plateau

Anthropogenic activities have substantially increased soil nutrient availability, which in turn affects ecosystem processes and functions, especially in nutrient-limited ecosystems such as alpine grasslands. Although considerable efforts have been devoted to understanding the responses of plant productivity and community composition to nitrogen (N) and phosphorus (P) enrichment, the nutrient enrichment effects on soil organic carbon (SOC) and microbial functions are not well understood. A four-year field experiment was established to evaluate the influence of continuous N and P enrichment on plant growth and SOC content in an alpine grassland of the Qinghai-Tibetan Plateau. The study included four treatments: Control without addition, N addition, P addition, and N plus P addition. N addition strongly increased aboveground plant biomass and decreased species richness by promoting growth of the dominant grasses species. In contrast, N and P enrichment significantly decreased SOC, especially the recalcitrant organic C content in the surface layer (0–10 cm) by reducing the slow C pool and enlarging the active C pool. Microbial biomass and activities of C-degrading enzymes (β-glucosidase, cellulase and polyphenol oxidase) and an N-degrading enzyme (chitinase) increased with nutrient inputs. The CO2 emissions during a 300 d incubation period were positively correlated with the cellulase and chitinase activities, while the slow C pool was negatively correlated with the cellulase and polyphenol oxidase activities. Consequently, N and P enrichment accelerated decomposition of the recalcitrant C by stimulating microbial growth and increasing enzyme activities, leading to negative impacts on soil C sequestration. Overall, the results indicate that alpine grassland soils of the Qinghai-Tibetan Plateau may be changing from a C sink to a C source under increasing N and P availability, and improvement of alpine grassland management through nutrient inputs should consider not only the aboveground biomass for grazing, but also the soil C sequestration and ecosystem functioning. © 2018 Elsevier B.V.

Luo R.1, 2 , Fan J.1 , Wang W.3, 4 , Luo J.5 , Kuzyakov Y. 6, 7, 8 , He J.-S.9 , Chu H.1 , Ding W.1
Elsevier B.V.
  • 1 State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China
  • 2 University of the Chinese Academy of Sciences, Beijing, 10049, China
  • 3 Department of Environment and Science, Dutton ParkQLD 4102, Australia
  • 4 Environmental Futures Research Institute, Griffith University, Nathan, QLD 4111, Australia
  • 5 AgResearch Limited, Ruakura Research Centre, Hamilton, 3240, New Zealand
  • 6 Agro-Technology Institute, RUDN University, Moscow, Russian Federation
  • 7 Department of Soil Science of Temperate Ecosystems, Department of Agricultural Soil Science, University of Göttingen, Büsgenweg 2, Göttingen, 37077, Germany
  • 8 Soil Science Consulting, Göttingen, 37077, Germany
  • 9 College of Urban and Environmental Sciences, Peking University, Beijing, 100871, China
Ключевые слова
Aboveground biomass; Alpine grassland; Carbon fractions; Enzyme activity; Nutrient enrichment; Species richness
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