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Table 3 Linear regression models m to explain foliar N and Mg concentrations without (m = 1) and with soil solution inorganic N in inorganic topsoil Nmin (m = 2) and througfall N deposition TFN (m = 3) for each tree species group

From: Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Species groupa

m

Estimates for intercept and regression coefficients for significant variables (at p < 0.1)

sd

sd resid

Adj R2

n

N concentration in foliage

Spruce

1

13.4*** + 0.0002 z

1.56

1.56

−0.02

39

2

14.0*** + 0.614 Nmin*** + 0.0001 z

 

1.24

0.34

 

3

13.5*** + 0.520 Nmin** + 0.040 TFN + 0.00006 z

 

1.2

0.36

 

Pine

1

11.9*−0.371 x*** + 0.165 y−0.008 z** + 0.119 BS*

2.41

1.31

0.65

27

2

12.3* + 0.447 Nmin −0.299 x** + 0.150 y−0.006 z +0.074 BS

 

1.23

0.67

 

3

6.2 + 0.110 Nmin +0.203 TFN**−0.152 x + 0.167 y−0.006 z* + 0.077 BS

 

1.04

0.76

 

Fir

1

11.5−0.0106 x + 0.0635 y + 0.0002 z−0.0097 BS

0.64

0.27

0.45

7

2

11.5−0.0040 Nmin −0.0105 x + 0.0648 y + 0.0002 z−0.0099 BS

 

0.27

−0.09

 

Beech

1

23.1***−0.137 x* + 0.002 z* + 0.003 trees

1.99

1.63

0.26

30

2

23.1***−0.022 Nmin −0.136 x* + 0.002 z* + 0.003 trees

 

1.63

0.23

 

3

22.9***−0.021 Nmin +0.008 TFN−0.136 x + 0.002 z* + 0.003 trees

 

1.63

0.19

 

Oak

1

30.3***−0.00003 z−0.03148 BS−0.00729 trees

3.49

2.54

0.29

13

2

31.0***−0.3419 Nmin +0.0008 z−0.0388 BS−0.0087 trees

 

2.5

0.23

 

3

28.6***−0.31952 Nmin +0.14423 TFN + 0.00003 z−0.02825 BS−0.00806 trees

 

2.42

0.18

 

Mg concentration in foliage

Spruce

1

0.965***−0.00007 P + 0.01697 CN

0.23

0.21

0.09

39

 

2

0.968*** + 0.00283 Nmin −0.00007 P + 0.01705 CN

 

0.21

0.06

 
 

3

0.967***−0.0017 Nmin +0.00209 TFN−9 10−5 P + 0.01642 CN

 

0.21

0.04

 

Pines

1

2.06***−0.001 P***−0.002 CN

0.31

0.23

0.4

27

 

2

2.18*** + 0.0671 Nmin −0.0017 P*** + 0.0005 CN

 

0.21

0.48

 
 

3

2.08*** + 0.095 Nmin *−0.012 TFN−0.0013 P**−0.0002 CN

 

0.2

0.51

 

Fir

1

5.02*−0.0007 P−0.1768 CN

0.57

0.35

0.41

7

 

2

6.10* + 0.166 Nmin −0.001 P−0.195 CN*

 

0.24

0.63

 
 

3

5.68* + 0.132 Nmin +0.046 TFN−0.002 P−0.150 CN

 

0.16

0.77

 

Beech

1

3.11* + 0.1828 Mgss*** + 0.0361 x**−0.0476 y−0.0003 z + 0.0034 BS

0.51

0.3

0.6

30

 

2

1.21*** + 0.0673 Nmin +0.1229 Mgss* + 0.0050 BS*−0.0002 P

 

0.34

0.48

 
 

3

1.41*** + 0.0620 Nmin −0.0193 TFN + 0.1368 Mgss* + 0.0047 BS*−0.0002 P

 

0.34

0.48

 

Oak

1

1.08*** + 0.194 Mgss* + 0.004 BS

0.33

0.23

0.41

13

 

2

1.07***−0.008 Nmin +0.200 Mgss* + 0.004 BS

 

0.23

0.34

 
 

3

1.23**−0.005 Nmin −0.010 TFN + 0.194 Mgss + 0.004 BS

 

0.23

0.29

 
  1. m model number, sd standard deviation of data (mg g−1), sd resid standard deviation of residuals (mg g−1), adj R2 adjusted R2, n number of plots, *p < 0.05, **p < 0.01, ***p < 0.001, x longitude, y latitude, z lower boundary of altitude class (m), P precipitation (mm), CN C/N ratio of the inorganic topsoil from 0− to 40−cm depth, BS base saturation (%) in the inorganic topsoil from 0− to 40−cm depth, Mgss Mg concentration in the soil solution from the inorganic topsoil from 0− to 40−cm depth, trees tree density (trees ha−1), Nmin inorganic N concentration in soil solution (mg L−1), TFN throughfall deposition of N (kg ha−1 year−1)
  2. aSpecies grouped as suggested by Stefan et al. (1997)
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Annals of Forest Science

ISSN: 1297-966X