Soils of a Mangrove Forest Composed ofRhizophora mucronataandBruguiera gymnorrhizafrom Ishigaki Island, Japan

Abstract

Elementary composition and absorption spectra of humic acids (HAs) and fulvic acids (FAs) obtained from 4 Canadian and 2 Japanese soils were determined, and the relationships between these 2 properties were discussed. In this study, FA refers to the PVP adsorbed, i.e. coloured substances in what has been designated, in previous reports, as FA. In 3 soil samples, FA was divided into the acid (pH l.O)-precipitable FAI and non-precipitable FA. fractions.1. In the case of HAs, some correlations were observed between the carbon content and hydrogen content or C/H ratio. The hydrogen and nitrogen contents of the FA and FAl samples tended to be higher while those of the FA. samples tended to be lower than those of HAs obtained from the same soils. In all cases, conspicuous differences in the elementary composition were found between the FAI and FA, fractions.2. The absorption spectra (logE vs. ). curves, in 0.1 N NaOH) of S out of 17 samples of HAs and FAs showed absorption bands due to the dissociation of the dihydroxyperylene quinone moiety (Pg). The absorption spectra of the other 12 samples were almost featureless. E,(E~6f;nm)' E,(El6f;nm)' E,.a(E~~nm) ' EJE.(E400nmIE600nm) and Pg content were adopted as parameters characterizing the spectra.3. The pH dependency of the absorption spectra was examined in solutions having various pHs.4. Several correlations were found between the parameters and the elementary composition of HAs and FAs. Based on the relation between the carbon content and El% values, FAs were divided into 2 groups. The elementary composition of each group showed distinct regularities.

The responses of early foliar litter humification to reduced snow cover during winter in an alpine forest

“…The degree of humification has generally been investigated with some indirect measurements (Milori et al 2002;Rosa et al 2005). Because the UV-visible spectra of humic substances are nearly straight on a logarithmic scale, the slopes of these spectra have been widely used as an index of the humification degree (Kumada et al 1967;Chen et al 1977;Kumada 1985). Moreover, the values of DlogK and E4/E6 decrease with changes in conjugation structures in the macromolecules of humic substances during the process of humification, so a lower DlogK or E4/E6 value serves to indicate a higher degree of humification degree.…”