Ecological Archives E096084A3
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/10.1890/131983.1
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 NH_{4}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 NH_{4}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 threeparameter exponential with a horizontal asymptote at c (y = aebx+ c) (green line), and Monod (y = a/(1 + bx1) (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)
(b) Plant biomass, regrowth after 14 months (kg/m²)
(c) Leaf N content (%)
(d) CH_{4} flux (mg CH_{4}·m^{2}·d^{1})
(e) Potential net N mineralization (μg NH_{4}N g^{1}·dry sediment·d^{1}) (The power function could not be fit.)
(f) CSM Extractable NH4 (μg NH_{4}N /g dry sediment)
(g) TRE Extractable NH4 (μg NH_{4}N /g dry sediment) (Note: The Monod function could not be fit.)
(h) TRE Sediment N content (kg/m²)