13C NMR spectroscopy characterization of particle-size fractionated soil organic carbon in subalpine forest and grassland ecosystems

Botanical Studies

Table 5 Relative intensities of CP/MAS ¹³C NMR spectra in different particle-size fractions in different sampling locations

Site	Particle size	% of C functional groups				HI^a	AR^b
Site	(μm)	Carboxyl	Aromatic	O-Alkyl	Alkyl	HI^a	AR^b
Forest	Coarse (>250)	6.71	13.72	45.52	34.04	0.92	14.71
	Large (250–53)	7.31	14.55	44.77	33.37	0.93	15.70
	Medium (53–20)	6.35	13.20	43.43	37.02	1.06	14.10
	Small (20–2)	7.12	11.14	43.32	38.43	1.11	11.99
	Fine (2–0.4)	8.91	7.73	40.75	42.62	1.25	8.48
	Very fine (<0.4)	5.61	10.46	45.18	38.74	1.03	11.08
Transition	Coarse (>250)	5.13	16.25	55.04	23.58	0.53	17.13
	Large (250–53)	6.95	21.20	49.27	22.58	0.59	22.78
	Medium (53–20)	6.90	19.19	47.75	26.16	0.71	20.61
	Small (20–2)	7.57	22.77	36.88	32.79	1.22	24.63
	Fine (2–0.4)	7.45	16.93	44.16	31.45	0.92	18.29
	Very fine (<0.4)	7.48	14.90	44.50	33.11	0.95	16.11
Grassland	Coarse (>250)	6.03	14.95	56.14	22.88	0.51	15.91
	Large (250–53)	6.78	16.79	53.95	22.48	0.53	18.02
	Medium (53–20)	7.54	18.49	51.01	22.96	0.58	20.00
	Small (20–2)	7.66	15.25	51.12	25.96	0.65	16.52
	Fine (2–0.4)	6.65	8.10	51.76	33.50	0.80	8.68
	Very fine (<0.4)	6.66	7.50	50.22	35.62	0.87	8.03

^aHumification degree of sampling soils: alkyl-C peak area (0–50 ppm)/O-alkyl-C peak area (50–110 ppm)
^bAromaticity ratio: aromatic-C peak area (110–165 ppm)/total peak area (0–165 ppm)