Recent publication
attested that in the urban forest of Brazzaville, litter decomposition is
faster with almost 45% of initial weight loss than in the dry season, where an
average loss of 26% in initial litter weight is noted (
Ifo et al., 2018). This
study was carried out in the urban forest of Brazzaville to follow the
decomposition of some organic compounds/secondary metabolites (reducing Sugars,
total Flavonoid and Polyphenols) of the leaves litters of two tropical species
Antiaris toxicaria Lesch and
Millettia laurentii De Wild. Thin-layer
chromatography and spectrophotometric assay of these metabolites were used on
the samples of litters collected in the field on various dates of follow-up of
the decomposition (0 d, 14 d, 28 d, 42 d, 56 d, 72 d and 84 d). The
chromatographic profile of initial litters shows a series of spots on yellow
florescence materializing presence of flavonoids, green fluorescence revealing
the presence of the acids phenols derived from the cinnamic acid. But the
chromatographic profile of the two litters in decomposition after two weeks
remains without structural information, being able to characterize the
decomposition of the chemical families highlighted in the initial litters.
Also, the analysis of quantitative total reducing sugar in the initial litters,
gives average concentrations of 64.4, 58.6, 57.5 g EG/kg Ms respectively for
the litters of
Millettia laurentii De
Wild,
Antiaris toxicaria Lesch and
the mixed litters (
Millettia laurentii and
Antiaris toxicaria).
Comparatively with the other types of litters, the initial average
concentrations in phenolic compounds (polyphenols and flavonoids totals) were the
highest for the litters of
Antiaris
toxicaria Lesch (27.3 g EAG/kg Ms and 13.07 g EC/kg Ms) (
P = 0.001). The losses of organic
chemical compounds are more significant during the first two weeks of
experiment than after this period.
Antiaris
toxicaria Lesch loses on average 43.8 g EG/kg Ms of reducing Sugars, 12.21
g EC/kg Ms of totals flavonoids and 26.4 g EAG/kg Ms of total polyphenols,
equivalent to 30% of loss of the initial weight. Average losses of 45.7 g EG/kg
Ms were obtained for reducing sugars, 1.5 g EC/kg Ms for totals flavonoids and
8.72 g EAG/kg Ms for totally phenols in for the litters of
Millettia laurentii, comparable to 24% in initial weight loss. This
study showed on the one hand, the direct link between rainfall and litters
decomposition and the losses in weight of the litters resulted in dissolution
in the water of the studied compounds.