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Partitioning sources of ecosystem and soil respiration (Reco and Rs) is important for understanding how climate change affects carbon cycling. Plant and microbial biomass analyses and daytime measurements of Reco and Rs were performed for 25 plots in an alpine meadow at elevation 4313 m on the Tibetan Plateau. Plant and microbial biomass were determined by harvesting method and the chloroform fumigation-extraction method, respectively. Respiration fluxes were measured by an automated CO2 flux system (LI-8100, LI-COR Biosciences, Lincoln, NE, USA). Soil respiration can be estimated by a linear or exponential relationship between Reco and aboveground plant biomass (AGB). Microbial respiration (Rm) can be estimated by a linear or exponential relationship between Rs and belowground plant biomass (BGB) or by a multiple relationship between Reco and AGB and BGB. Soil respiration (or Rm) is respiration flux when AGB (or BGB) is extrapolated to zero for the linear and exponential regression methods. Similarly, Rm is respiration flux when both AGB and BGB are zero for the multiple regression method. Our findings suggest that the exponential regression method to partition sources of Reco and Rs may be more appropriate compared to other methods for this alpine meadow of Tibet.
One-year-old seedlings of silver birch (Betula pendula Roth.) were grown in pots filled with a soil substrate that originated from an area polluted by a phosphate fertiliser factory and characterised by a high soil Al level and low Ca/Al ratio or with a substrate from an area regarded as free from toxic pollution. In addition the effect of fertilisation with a mixture of nutrients was evaluated. Birch seedlings grew slowest in the unfertilised polluted substrate. In the unfertilised polluted substrate seedlings were characterised by high biomass allocation to roots (60% vs. 30 to 40% in control or fertilised substrate), lower diversity of ectomycorrhizae and the lowest rate of root and substrate microbial respiration. Roots of seedlings grown in the polluted soil were characterised by a significantly higher level of phenolic compounds. Fertilisation of plants grown in the polluted soil accelerated their growth, and lowered RWR (g root g-1 plant) and increased biomass allocated to foliage. Our results indicate that elimination of air pollution does not decrease the toxic effect of a polluted soil. Fertilisation may improve the condition of seedlings growing in polluted soil, however it was not able to eliminate entirely the adverse effect of soil pollution.
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