Effects of ecological succession on chemical characteristics of humic and fulvic acids in a Japanese volcanic ash soil

摘要

To obtain further details regarding effects of ecological succession on chemical characteristics of humic and fulvic acids in a Japanese volcanic ash soil, humus quantitative analysis, HPSEC, and liquid-state 13C NMR analysis were performed with surface mineral soils (0-20 cm). Grassland at site 1 has been maintained by mowing, while the maintenance of sites 2 (pine forest) and 3 (broad-leaved forest) was discontinued approximately 30 and more than 100 years ago, respectively. The concentration of humic acids decreased from 60.4 to 47.4 C g/kg in only 30 years (site 1 vs. site 2), and then decreased from 47.4 to 30.2 C g/kg after 100 years (site 2 vs. site 3). Simultaneously, the concentration of fulvic acids decreased only slightly throughout the series (site 1 to site 3). Physicochemical properties appeared to be affected by succession only in humic acids. In particular, the proportion of aryl C moieties in the humic acid of site 2 decreased from 49.6 to 31.4%, a level similar to that of site 3.The findings of this study clearly demonstrate that humic acids, but not fulvic acids, significantly changed with decreasing aryl C content, over the first 30 years and then remained fairly constant.