Correlation Between CO2 Efflux and Net Nitrogen Mineralization and Its Response to External C or N Supply in an Alpine Meadow Soil

In nutrient-limited alpine meadows, nitrogen (N) mineralization is prior to soil microbial immobilization; therefore, increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils. In addition, low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization. A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau. Two levels of NH4NO3 (N) or glucose (C) were added, with a blank without addition of C or N as the control, before incubation at 5, 15, or 25 degrees C for 28 d. CO2 efflux was measured during the 28-d incubation, and the mineral N was measured at the beginning and end of the incubation, in order to test two hypotheses: 1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive. The results showed a negative correlation between CO2 efflux and net N immobilization in the control. External inorganic N supply did not change the negative correlation. The external labile C supply shifted the linear correlation from negative to positive under the low C addition level. However, under the high C level, no correlation was found. These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures. Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.