Figure 1. Component 1 vs component 2 of the partial least squares discriminant analysis (PLS-DA) of the elemental, stoichiometric and metabolomic variables in Quercus ilex leaves for data of all seasons. (a) Component 1 and (b) component 2 of the stoichiometric and metabolomic variables. Carbon (C) : nitrogen (N) : phosphorus (P) : potassium (K) ratios are shown in red. Different metabolomic families are indicated by different colors: blue, sugars; green, amino acids; cyan, nucleotides; violet, phenolics; yellow, related compounds of amino acid and sugar metabolism (RCAAS); brown, terpenes; dark blue, overlapped nuclear magnetic resonance (NMR) signals, and light orange, nonpolar metabolites. Acronyms and abbreviations are used for some of the variables and a number has been assigned to each metabolite forming part of the overlapped NMR signals: sucrose (Suc; 1), α-glucose (αG; 2), β-glucose (βG; 3), hexose (Hex), pentose (Pent), disaccharide (Disacch), lactic acid (11), citric acid (4), alanine (Ala; 5), isoleucine (Ile; 6), threonine (Thr), valine (Val; 7), leucine (Leu), phenylalanine (Phen), proline (Pro), arginine (Arg), tryptophan (Trp), tyrosine (Tyr), quercitol (8), quinic acid (9), choline (10), N-acetyl group (12), polyphenol (13), fatty acids (FA), unsaturated fatty acids (UFA), polyunsaturated fatty acids (PUFA), diacylglycerides (DGA), triacylglyceride 1 (TGA1), triacylglyceride 2 (TGA2), aldehyde group (Ald), acetyl group (Acetyl), linoleyl fatty acid (Linoleyl FA), overlapped NMR signals (O1–O10): O1, 5 + 10 + 2 + 1; O2, 10 + 2 + 1; O3, 10 + 3 + 1; O4, 4 + 13; O5, 6 + 7; O6, 11 + unknown, O7, 11 + 12, O8, 8 + 9; O9, 8 + 9 + 2 + 3 + 1 and O10, 8 + 1. Unassigned metabolites are not represented in the variable plot. (c) Samples categorized by season and drought treatment. Seasons are indicated by different colors (green, spring; red, summer; yellow, autumn; blue, winter). Control and drought trees are indicated by asterisks and triangles respectively. Capital letters indicate the mean component 1 vs component 2 scores for the treatments in each season (C, control trees; D, droughted trees). Variables marked with asterisks showed statistical significance (P < 0.05) or marginal statistical significance (P < 0.1) in one-way ANOVAs (Supporting Information Table S5).
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