Table 1 Results of repeated-measures analysis of covariance (ANCOVA) testing the effects of the frequency and rate of N addition on aboveground net primary productivity (ANPP) for community (COM) and species, L.c., Leymus chinensis, A.c., Agropyon cristatum, C.s., Cleistogenes squarrosa, K.c., Koeleria cristata, C.k., Carex korshinskyi, A.t., Allium tenuissimum, and Ch.g., Chenopodium glaucum, using the N-rate as the continuous variable and the initial value in 2008 as a covariate (V0) across 2009–2013.

From: Productivity depends more on the rate than the frequency of N addition in a temperate grassland

 

df

COM

L.c.

A.c.

C.s.

K.c.

C.k.

A.t.

Ch.g.

V0

1,176

0.2

21.4***

13.9***

63.1***

131.4***

10.7**

19.3***

0.3

N-rate (N)

1,176

247.2***

85.6***

9.2**

26.3***

20.0***

10.2**

17.5***

20.9***

N frequency (F)

1,176

0.6

1.9

1.2

1.1

0.0

2.3

0.2

0.1

Year (Y)

4,704

7.0***

12.0***

4.8**

3.7*

6.1***

1.4

0.6

8.5***

Y × N

4,704

40.5***

48.8***

2.5

1.5

2.8*

0.6

0.4

8.0***

Y × F

4,704

0.7

1.5

1.1

0.9

0.3

1.3

0.4

0.1

Regression parameters

Slope

2 N

76.0***

55.0*

13.3

−2.2*

−0.4

−2.4

−0.3*

3.5**

12 N

92.9***

42.8*

32.6*

−1.9**

−1.5**

−2.1

−0.3**

3.4***

  1. Asterisks denote significant levels: *P < 0.05; **P < 0.01; and ***P < 0.001, respectively.
  2. Regression parameters were estimated using log-linear model with N-rate as the continuous predictor, i.e., ANPP = Intercept + Slope × log10(N + 1). 2 N = 2 N additions yr−1 and 12 N = 12 N additions yr−1, respectively.
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