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Table 1 Response ratios of sugars and organic acids (HA-treated vs control)

From: Humic acids increase the maize seedlings exudation yield

  Root extract Exudates   Root extract Exudates
Carbohydrates metabolism—glycolysis Compounds related to stress response
 Glycerol − 2.02* 2.12 *  Trehalose − 1.28 4.56*
 Glucose-6-phosphate − 1.68 15.48*  Salicylaldehyde − 2.55 3.45*
 Glycerol-3-galactoside − 1.12 12.31*  Tagatose − 1.52 29.93*
 6-Deoxyglucose − 1.66 6.93*  Beta-gentiobiose − 1.64 8.13*
 Glycerol-alpha-phosphate 1.27 3.84* TCA cycle
 Glucose − 1.12 1.59*  Alpha-ketoglutarate 1.75* 4.25*
 Glucose-1-phosphate 1.04 1.41  Isocitric acid 2.74 12.16*
Pentose pathway  Aconitic acid − 1.46 18.81*
 Ribose − 2.05* 3.14*  Itaconic acid − 1.48 2.52*
 Erythritol − 1.71 11.20*  Succinic acid − 1.37 11.85*
 Ribitol − 1.40 9.07*  Malic acid 1.73 25.84*
General carbohydrates metabolism  Maleic acid 1.40 2.08*
 Sophorose − 3.94* 66.51*  Fumaric acid − 1.49 5.92*
 Sorbitol − 3.02* 11.85* Compounds linked to stress response
 Mannose − 6.79* 6.05*  2-Deoxytetronic acid − 3.31* 12.39*
 Methyl O-d-galactopyranoside − 1.15 66.97*  Threonic acid − 1.13 5.07*
 Xylonolactone − 2.57 59.29*  Isothreonic acid − 2.25 8.25*
 Lyxose − 1.45 9.31*  Citramalic acid − 1.72 13.24*
 Fructose 1.08 8.51*  Mucic acid − 1.09 7.45*
 Levoglucosan 1.06 7.19* Compounds linked to pentose pathway
 Lyxitol − 1.49 6.89*  Gluconic acid − 1.94* 8.28*
 Xylulose − 1.49 5.50*  Pyruvic acid − 1.96 1.56*
 Xylose − 1.46 5.24*  Ribonic acid − 2.01 − 1.04
 Methylhexose − 1.26 4.82* Compounds linked to carbohydrates metabolism
 Xylitol − 1.86 4.10*  Lactic acid − 4.80* 12.59*
 Hexose-6-phosphate − 1.45 3.13*  Glycolic acid − 1.65* 2.71*
 Fructose-6-phosphate − 1.59 2.63*  3-Hydroxypropionic acid − 1.40* 2.04*
 Maltotriose − 4.83* 1.34  4-Hydroxybutyric acid − 1.95* 2.80*
 Maltose − 4.86* 2.43  Glyceric acid − 1.79 13.51*
 Maltitol 1.89 2.42  3-Hydroxybutyric acid 1.29 5.26*
 Sucrose 1.55 3.24  2-Hydroxyvaleric acid 4.64 2.43*
 Lactitol − 1.17 10.86  Galactonic acid − 1.29 1.52
 Fucose − 1.86 3.25  2-Hydroxyglutaric acid − 1.47 2.59
Carbohydrates metabolism—cell wall  2-Hydroxybutanoic acid − 1.31 2.18
 Galactose − 1.62 9.01*    
 Galactinol 1.20 10.54*    
 3,6-Anhydro-d-galactose − 1.04 3.23*    
  1. When the response ratio (level in a given treatment divided by the level in the control) was lower than 1 the inverse was taken, and the sign changed. Values in italic type and indicated by * represent a Dunnett’s test significance of p < 0.05 against the control