Gross nitrogen ammonification and nitrification rates
Nitrogen addition level and frequency had significant effects on both gross ammonification (GA, P < 0.05) and gross nitrification rates (GN, P < 0.05) while mowing showed no significant effects on GA and GN. Besides, the interaction of N addition level and N addition frequency was significant for GA (P< 0.001), but not for GN. In contrast, there were significant interactions between mowing and N addition level or N addition frequency on GN (P < 0.01), but not on GA (Table 2).
Across the N addition levels, the highest N addition (N-50) significantly increased GA by 278.45% (P < 0.05). For the lowest addition level (N-2), GA was significantly decreased by 44.61% (P < 0.05), but was not significantly changed at higher N addition levels (N-10, N-20) with mowing (Fig. 2a, Table 2). Higher N addition levels (N-10, N-20) significantly increased GN by 398.61% and 548.75% (P < 0.05, Fig. 2b). N addition with mowing significantly increased GN (P < 0.05, Fig. 2b). However, the frequency of N addition and mowing had no interactive effects on GN (Fig. 2b).