Fig 1.
Box plots showing the variability among five different Populus taxa (left panels) and between the Monroe and Pontotoc sites (right panels).
Bars with different letters indicate statistically significant differences (P-value < 0.05). Parameters include maximum carboxylation rate of Rubisco (Vcmax) by (a) taxa and (b) site, maximum electron transport limited carboxylation rate (Jmax) by (c) taxa and (d) site, triose phosphate utilization limited carboxylation rate (TPU) by (e) taxa and (f) site, nitrogen per unit leaf area (Narea) by (g) taxa, (h) site, and tree biomass by (i) taxa and (j) site. D×T and T×D taxa were combined and shown as D×T, and (D×N)×M was included in D×N (S1 Table). D×D = P. deltoides × P. deltoides, D×M = P. deltoides × P. maximowiczii, D×N = P. deltoides × P. nigra, D×N×M = P. deltoides × P. nigra × P. maximowiczii, D×T = P. deltoides × P. trichocarpa, T×D = P. trichocarpa × P. deltoides, and T×M = P. trichocarpa × P. maximowiczii.
Fig 2.
Leaf reflectance curves of five different Populus taxa.
D×T and T×D taxa were combined and shown as D×T, and taxa (D×N)×M was included in D×N (S1 Table). D×D = P. deltoides × P. deltoides, D×M = P. deltoides × P. maximowiczii, D×N = P. deltoides × P. nigra, (D×N)×M = P. deltoides × P. nigra × P. maximowiczii, D×T = P. deltoides × P. trichocarpa, T×D = P. trichocarpa × P. deltoides, and T×M = P. trichocarpa × P. maximowiczii.
Table 1.
Pearson correlation coefficient (r) matrix among tree biomass, Vcmax, Jmax, TPU, and Narea.
Fig 3.
Scatterplots showing the linear relationship between measured and estimated Vcmax, Jmax, TPU and Narea for the LASSO models: (a), (b), (c), and (d) and the PCA models: (e), (f), (g), and (h).
The solid black line is the regression line, and the dotted red line is the 1:1 line.
Table 2.
Selected predictor variables in the models and averaged 10-fold cross validation results.
Fig 4.
Lollipop plot showing the loadings of all spectral wavelengths in (a) PC1 and (b) PC2.
As shown by vertical green dashed line, a significant peak and trough occurred at or near 935 nm, which was also selected by the LASSO models for estimating Vcmax and Jmax.
Table 3.
Comparison of model performance among the LASSO model, the PCA model, and published vegetation indices.