Spatial Variations in Concentration, Compositions of Glomalin Related Soil Protein in Poplar Plantations in Northeastern China, and Possible Relations with Soil Physicochemical Properties

Figure 1

Schematic diagram with partition method of functional traits of GRSP by using infrared spectrum. Note: functional trait I (wave number of 3750–3000 cm⁻¹) is a mixture of O–H stretching of carboxylic acid, phenols, alcohols, clay minerals and oxides, N–H stretching of organic amines, amides, and aromatic C–H stretching. Functional trait II (wave number of 3000–2820 cm⁻¹) is aliphatic C–H stretching. Functional trait III (wave number of 1750–1480 cm⁻¹) is a mixture of C=O stretching of carboxylic acid, ketones and amides, and asymmetric COO– stretching of carboxylic acid salts. Functional trait IV (wave number of 1480–1320 cm⁻¹) is a mixture of symmetric COO– stretching of carboxylic acid salts and C–H bending of –CH₂– and –CH₃ groups. Functional trait V (wave number of 1320–1200 cm⁻¹) is a mixture of C–O stretching and O–H bending of –COOH. Functional trait VI (wave number of 1200–930 cm⁻¹) is a mixture of C–O stretching of polysaccharide and Si–O–Si stretching in clay minerals and oxides. Functional trait VII (wave number of 930–840 cm⁻¹) is O–H bending of structural OH in clay minerals and oxides.