| Abstrakt: |
Nitrogen availability affects decomposition of soil organic carbon (SOC), and hence impacts soil quality. It remains unclear whether N availability determines the direction of SOC transformation and how this may interact with C availability in soil. Nitrogen-deficient topsoil from two depths (0-5 cm, Soil5; 5-10 cm, Soil10) were supplied with eight rates of Ca(NO3)2(0-160 mg N kg−1soil), and incubated for four weeks. Two experiments, with and without weekly addition of glucose at 0.5 mg C g−1, were conducted. Without glucose, N addition at 40-80 mg kg−1to Soil5 stimulated CO2release, but further supply up to 120 mg kg−1showed no effect on CO2release in Week 1. Compared with N addition alone, glucose addition lowered N requirement (20 vs.40 mg kg−1) for the peak CO2release in Soil5, indicating that labile-C supply decreased N demand for microbial activity. With glucose addition, CO2release rates in Soil5 remained constant at N supply ranging from 20 to 160 mg kg−1. In contrast, CO2release rates in Soil10 was affected by N supply only when glucose was supplied, suggesting the important role of C availability in regulating N-induced CO2efflux in soil. Irrespective of N supply, specific CO2release per unit SOC following glucose addition was higher in Soil10 than Soil5, albeit no differences between two soils without glucose addition. These results suggest that enhanced N availability up to 20-40 mg kg−1favors soil CO2release when C availability is not limiting. |
