Properties of neutral phosphate buffer extractable organic matter in soils revealed using size exclusion chromatography and fractionation with polyvinylpyrrolidone

Figures & data

Table 1 Properties of the soil samples used

Soil	Soil type	Land use	pH (H2O)	Total C (g kg^−1)	Total N (g kg^−1)	C/N
Fujisaki	Brown Lowland soil	Chestnut orchard	6.3	29.5	2.1	9.9
Fukushima	Ando soil	Upland field	5.9	91.1	5.2	17.7
Nayoro	Gray Lowland soil	Upland field	6.4	27.0	2.3	11.8

Figure 1  Size exclusion chromatograms of the whole neutral phosphate buffer (NPB) extracts. The moluecular weights (MWs) indicated in the figure were estimated using polyethylene glycols as standards. AU, absorbance unit; RFU, relative fluorescence unit.

Figure 2  Ultraviolet (UV) absorption spectra and fluorescence emission spectra obtained for bovine serum albumin and the broad peaks of whole neutral phosphate buffer (NPB) extracts.

Table 2 Contents of organic C, organic N and Coomassie Blue-reactive substances (CBRS) and their distribution among the fractions

Soil	Fraction	Organic C		Organic N		C/N	CBRS
		mg kg^−1	Distribution(%)	mg kg^−1	Distribution(%)		mg kg^−1 ^†	Distribution (%)	CBRS-N/organic N^‡
Fujisaki	Whole	663	100	80	100	8.2	215	100	43
	HA	43	6	6	8	7.0	62	29	163
	PVP-adsorbed FA	156	24	9	11	17.1	63	29	111
	PVP-non-adsorbed FA	469	71	65	80	7.2	90	42	22
Fukushima	Whole	933	100	69	100	13.5	254	100	59
	HA	77	8	8	12	9.3	35	14	67
	PVP-adsorbed FA	300	32	11	17	26.3	83	33	116
	PVP-non-adsorbed FA	586	63	51	74	11.5	137	54	43
Nayoro	Whole	809	100	104	100	7.8	306	100	47
	HA	100	12	10	9	10.2	79	26	128
	PVP-adsorbed FA	212	26	11	11	18.8	82	27	117
	PVP-non-adsorbed FA	491	61	82	79	6.0	149	49	29
^†Equivalent to bovine serum albumin.
^‡Calculated from the N content of bovine serum albumin. FA, fulvic acid; HA, humic acid; PVP, polyvinylpyrrolidone.

Figure 3  Size exclusion chromatograms of the humic acid (HA), polyvinylpyrrolidone (PVP)-adsorbed fulvic acid (FA) and PVP-non-adsorbed FA fractions monitored by absorption at 280 nm. The molecular weights (MWs) indicated in the figure were estimated using polyethylene glycols as standards. AU, absorbance unit.

Figure 4  Ultraviolet (UV) absorption spectra and fluorescence emission spectra obtained for the broad peaks of the humic acid (HA), polyvinylpyrrolidone (PVP)-adsorbed fulvic acid (FA) and PVP-non-adsorbed FA fractions.

Figure 5  Amounts of organic C and N in the incubated (□) and unincubated (

) whole neutral phosphate buffer (NPB) extracts and their fractions. Vertical bars indicate standard error. NS, not significant at P = 0.05. *P < 0.05; **P < 0.01; ***P < 0.001 (Student's t-test). FA, fulvic acid; HA, humic acid; PVP, polyvinylpyrrolidone.

Figure 6  Size exclusion chromatograms of the whole neutral phosphate buffer (NPB) extracts and their fractions before (----) and after (–––) incubation. FA, fulvic acid; HA, humic acid; PVP, polyvinylpyrrolidone.