Table 2 Summary of the best-fit models of log-transformed aboveground plant biomass (APB) with one or two quadratic terms, without and with multiplicative interactions

From: Interactive and unimodal relationships between plant biomass, abiotic factors, and plant diversity in global grasslands

X1

X2

Model structure

P value

P value

interaction

X1 and X2

P value

interaction

X12 and X2

Multiple R2

Adjusted R2

MAP

MAT

Y ~ X1*X2 + X12*X2

< 0.001

0.079

0.034

0.42

0.36

MAP

TDry

Y ~ X1 + X2 + X12 + X22

< 0.001

-

-

0.41

0.36

MAP

Clay

Y ~ X1 + X12 + X2

< 0.001

-

-

0.38

0.34

N

Sha

Y ~ X1*X2 + X12*X2

< 0.001

0.027

0.025

0.38

0.32

NDep

Sha

Y ~ X1*X2 + X12*X2

0.004

0.122

0.030

0.29

0.21

  1. Shown is the best-fit model for each set of predictors, selected based on the AIC (for model comparisons see Supplementary Table S1). Depicted are the P values of the models and the coefficients of determination (multiple and adjusted R2). For the models with interactions, the P values of the interactions are given. All models were calculated based on site-level data for all sites with data on soil clay content (N = 55). The independent variables (X) were centered and APB was log-transformed (natural logarithm).
  2. MAP mean annual precipitation, MAT Mean annual temperature, TDry mean temperature of driest quarter of the year, Clay soil clay content, N soil total nitrogen content, Sha Shannon index of plant diversity, NDep atmospheric nitrogen deposition.
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