EFFECTS OF ARTIFICIAL NITROGEN AND PHOSPHORUS DEPOSITIONS ON SOIL RESPIRATION in TWO PLANTATIONS IN SOUTHERN CHINA

In the present study, atmospheric nitrogen (N) and phosphorus (P) depositions were simulated with NH4NO3 and KH2PO4 solutions respectively to investigate the effects of N and P depositions on soil respiration in two plantations in southern China. The annual soil respiration rate under the control plot was 3190 ± 39.4 g CO2 m^-2 and in the Acacia mangium and Eucalyptus urophylla plantations, the rate was 5180 ± 72.2 g CO2 m^-2. Results of the field experiment showed that both N and P treatments promoted soil respiration rates under A. mangium but significantly decreased the soil respiration under E. urophylla. The lower level (5 ppm) P treatment significantly enhanced soil respiration rates in A. mangium and E. urophylla plantations. However, with the increase in P concentration, the soil respiration rates decreased under A. mangium but increased under E. urophylla. Soil respiration rates exhibited significant fluctuation and approached to nearly equal values at the end of the experiment.