Ecological Archives E096-084-A3

Lucía Vivanco, Irina C. Irvine, and Jennifer B. H. Martiny. 2015. Nonlinear responses in salt marsh functioning to increased nitrogen addition. Ecology 96:936–947. http://dx.doi.org/10.1890/13-1983.1

Appendix C. Model fitting of plant, microbial, and sediment responses to nitrogen addition gradient, and a figure showing data fitting to five models and their Akaike values are presented.

Table C1. Results of fitting data to a linear, power, exponential, exponential with asymptote and Monod functions. The preferred model was selected based on the highest Akaike weight (in bold).

 

 

Linear function

Power function

Exponential function

Exponential with asymptopte function

Monod function

Plant characteristics

 

 

 

 

 

 

Plant biomass_7 months (kg/m²)

 

 

 

 

 

 

 

AICc

0.18

25.69

0.33

2.28

25.78

 

Akaike weight

0.44

0

0.41

0.15

0

Plant regrowth_14 months (kg/m²)

 

 

 

 

 

 

 

AICc

11.62

17.42

13.47

7.19

18.2

 

Akaike weight

0.09

0.01

0.04

0.86

0

Leaf N content (%)

 

 

 

 

 

 

 

AICc

9.9

31.68

10.26

1.32

31.7

 

Akaike weight

0.01

0

0.01

0.98

0

Microbial processes

 

 

 

 

 

 

Methane flux (mg m-2 d-1)

 

 

 

 

 

 

 

AICc

1.55

3.58

1.9

4.01

4.08

 

Akaike weight

0.36

0.13

0.3

0.11

0.1

Potential net N mineralization  (μg NH4-N·g-1 dry sediment·d-1)

 

 

 

 

 

 

 

AICc

-4.14

-

1.47

-3.79

-4.18

 

Akaike weight

0.34*

-

0.02

0.29

0.35

Sediment characteristics

 

 

 

 

 

 

Total N (kg/m²)

 

 

 

 

 

 

 

TRE

 

 

 

 

 

 

AICc

-18.88

-8.87

-21.86

-23.95

-6.69

 

Akaike weight

0.06

0

0.25

0.7

0

Extractable ammonium  (μg NH4-N /g dry sediment)

 

 

 

 

 

 

 

CSM

 

 

 

 

 

 

AICc

59.04

59.64

65.59

60.74

59.36

 

Akaike weight

0.33

0.24

0.01

0.14

0.28

 

TRE

 

 

 

 

 

 

AICc

42.42

47.82

33.64

32.94

-

 

Akaike weight

0.01

0

0.41

0.58

-

*Data fit to linear and Monod functions similarly. Linear function was prefered due to parsimony.

 

Fig. C1. (below) Responses to the N addition gradient. The best fits of five functions to each dataset are shown: linear (y = ax + b) (black line), power (y = axb) (blue line), exponential with a horizontal asymptote at zero (y = aebx) (red line), a three-parameter exponential with a horizontal asymptote at c (y = aebx+ c) (green line), and Monod (y = a/(1 + bx-1) (orange line), where x is nitrogen concentration, and a, b, and c are constants. Each data point (circles) is an average ofn = 15, exceptfor panels (f) - (h) where n = 5 (see Methods).

(a) Plant biomass, total harvest after 7 months (kg/m²)

a

(b) Plant biomass, regrowth after 14 months (kg/m²)

b

(c) Leaf N content (%)

c

 

(d) CH4 flux (mg CH4·m-2·d-1)

d

 

(e) Potential net N mineralization (μg NH4-N g-1·dry sediment·d-1) (The power function could not be fit.)

e

(f) CSM Extractable NH4 (μg NH4-N /g dry sediment)

f

(g) TRE Extractable NH4 (μg NH4-N /g dry sediment) (Note: The Monod function could not be fit.)

g

(h) TRE Sediment N content (kg/m²)

h


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