Effect of N addition, moisture, and temperature on soil microbial respiration and microbial biomass in forest soil at different stages of litter decomposition

Purpose The objective of the present study was to investigate the interactive effects of nitrogen (N) addition, temperature, and moisture on soil microbial respiration, microbial biomass, and metabolic quotient (qCO(2)) at different decomposition stages of different tree leaf litters. Materials and methods A laboratory incubation experiment with and without litter addition was conducted for 80 days at two temperatures (15 and 25 degrees C), two wetting intensities (35 and 50 % water-filled porosity space (WFPS)) and two doses of N addition (0 and 4.5 g N m(-2), as NH4NO3). The tree leaf litters included three types of broadleaf litters, a needle litter, and a mixed litter of them. Soil microbial respiration, microbial biomass, and qCO(2) along with other soil properties were measured at two decomposition stages of tree leaf litters. Results and discussion The increase in soil cumulative carbon dioxide (CO2) flux and microbial biomass during the incubation depended on types of tree leaf litters, N addition, and hydrothermal conditions. Soil microbial biomass carbon (C) and N and qCO(2) were significantly greater in all litter-amended than in non-amended soils. However, the difference in the qCO(2) became smaller during the late period of incubation, especially at 25 degrees C. The interactive effect of temperature with soil moisture and N addition was significant for affecting the cumulative litter-derived CO2-C flux at the early and late stages of litter decomposition. Furthermore, the interactive effect of soil moisture and N addition was significant for affecting the cumulative CO2 flux at the late stage of litter decomposition but not early in the experiment. Conclusions This present study indicated that the effects of addition of N and hydrothermal conditions on soil microbial respiration, qCO(2), and concentrations of labile C and N depended on types of tree leaf litters and the development of litter decomposition. The results highlight the importance of N availability and hydrothermal conditions in interactively regulating soil microbial respiration and microbial C utilization during litter decomposition under forest ecosystems.