Changes in the SOM composition along the grazing-exclusion grassland chronosequence.

† GE0, free grazing; GE4, 4-year grazing exclusion; GE7, 7-year grazing exclusion; GE11, 11-year grazing exclusion; GE31, 31-year grazing exclusion.‡ HAC, Humic acid carbon; FAC, Fulvic acid carbon; HUC, Humin carbon; Extractable humus C, Extractable humus carbon;HAC/FAC, The ratio of humic acid carbon to fulvic acid carbon; HAC/extractable humus C, The ratio of humic acid carbon to extractable humus carbon.§ Data were represented as mean ± SD (n = 3). The same superscript letters within each column indicated no significant difference at P Changes in the SOM composition along the grazing-exclusion grassland chronosequence.