Table 2 Effects of N addition levels and methods on NO₃⁻-N concentrations in soil planted with four tree species during the experimental period

AM

Jun.2012

30.3 ± 10.1a

22.7 ± 5.4ab

14.5 ± 3.2bc

11.7 ± 3.9bc

5.6 ± 1.3c

2.3 ± 1.5c

Dec.2012

43.6 ± 2.2a

14.0 ± 3.7bc

3.5 ± 1.8d

19.0 ± 2.5b

5.8 ± 4.5 cd

3.0 ± 4.1d

Apr.2013

106.2 ± 8.3a

12.9 ± 11.4b

7.1 ± 6.4b

69.1 ± 15.0a

5.2 ± 1.7b

4.9 ± 4.6b

Jul.2013

139.2 ± 14.0a

23.4 ± 8.5b

7.3 ± 9.5b

34.3 ± 11.5b

10.0 ± 8.9b

16.4 ± 0.7b

Nov.2013

130.2 ± 16.3a

59.0 ± 8.1b

20.8 ± 7.0b

55.5 ± 15.0b

17.8 ± 8.3b

18.7 ± 6.6b

OP

Jun.2012

49.4 ± 6.1a

44.9 ± 7.6ab

31.3 ± 3.1c

41.2 ± 4.4bc

52.2 ± 6.8a

28.3 ± 2.1c

Dec.2012

38.0 ± 6.2a

16.7 ± 3.4bc

4.7 ± 1.5c

20.5 ± 10.4ab

14.9 ± 10.3bc

3.8 ± 1.3c

Apr.2013

69.0 ± 17.5a

13.2 ± 2.6b

5.8 ± 3.4b

50.0 ± 6.3a

18.4 ± 5.3b

5.9 ± 3.3b

Jul.2013

89.3 ± 7.4a

31.8 ± 10.7b

5.5 ± 0.4c

31.1 ± 7.9b

14.7 ± 9.2bc

3.6 ± 3.4c

Nov.2013

87.5 ± 6.1a

24.1 ± 2.9b

2.8 ± 1.7d

27.2 ± 6.3b

18.1 ± 8.3bc

5.9 ± 2.1 cd

SS

Jun.2012

47.3 ± 9.1a

46.4 ± 4.4ab

20.9 ± 7.2c

37.4 ± 9.8abc

29.0 ± 2.8bc

24.3 ± 4.8bc

Dec.2012

48.0 ± 6.7a

26.3 ± 5.0b

10.8 ± 3.9c

19.2 ± 5.4bc

15.0 ± 5.4bc

8.9 ± 2.2c

Apr.2013

65.2 ± 7.5ab

37.3 ± 15.8bc

14.2 ± 1.3c

74.4 ± 19.8a

25.8 ± 12.4c

14.6 ± 3.9c

Jul.2013

70.0 ± 17.2a

30.8 ± 3.1b

7.9 ± 0b

65.3 ± 14.6a

25.9 ± 6.5b

15.9 ± 9.7b

Nov.2013

75.3 ± 10.3a

38.7 ± 4.2c

8.0 ± 2.0d

56.9 ± 4.6b

20.1 ± 2.8d

15.4 ± 3.0d

PM

Jun.2012

30.6 ± 9.5b

42.3 ± 10.3ab

35.8 ± 2.5ab

54.3 ± 1.2a

50.0 ± 5.8ab

34.7 ± 2.0ab

Dec.2012

39.6 ± 5.0b

26.8 ± 5.1c

12.5 ± 5.1d

57.9 ± 3.6a

30.1 ± 1.0bc

15.3 ± 2.2d

Apr.2013

59.4 ± 27.5ab

46.5 ± 15.8ab

31.7 ± 1.2ab

100.7 ± 6.5a

45.8 ± 8.6ab

25.2 ± 6.0b

Jul.2013

86.5 ± 15.5a

73.7 ± 15.7a

17.1 ± 7.2b

95.3 ± 14.8a

73.5 ± 26.3a

51.0 ± 8.8ab

Nov.2013

121.5 ± 13.7a

38.4 ± 1.9bc

18.5 ± 10.0c

112.5 ± 21.6a

71.3 ± 19.7b

40.7 ± 2.1bc