Soluble Organics from Forest Litter and their Role in Metal Dissolution

Abstract

The effect of soluble organics from O1 and O2 litter of seven overstory and understory forest species on dissolution of Al, Fe, Mg, and Mn from two forest soils was investigated. Litter was leached in absence and presence of soil under controlled laboratory conditions, and the leachates were analyzed. In absence of soil, different litters varied widely in their ability to release dissolved organic carbon (DOC) and metals. No significant correlations (p > 0.1) between protons consumed and DOC, Al, Mg, and Mn released from litter were found. In the presence of soils there was a direct relationship between organics released from litters and Al and Fe dissolved from soils but not for the other two metals. The predominant class of organics found in all litter leachates were acids and neutrals, and their contents were directly proportional to total organics dissolved. Thus, hydrophobic plus hydrophilic acid, base, and neutral content of litter leachates corresponded to mean values of 49.6, 8.8, and 41.1%, respectively, for all litters. Total acid content was composed of 30.6% hydrophobics and 18.5% hydrophilics. A good correlation was obtained between soil dissolved Al and hydrophobic acids (r = 0.91, p < 0.001), Al and Fe, and hydrophilic acids (r = 0.93, r = 0.85, p < 0.001, respectively). Polyphenolics constituted from 10 to 23% of the DOC content of both O1 and O2 litter extracts. Polyphenolic content was highly correlated with dissolved Al (r = 0.94, p < 0.001) and with dissolved Fe (r = 0.80, p < 0.001). Five aliphatic acids and six aromatic acids were detected and quantified. Free‐organic acids with high chelating abilities such as oxalic, malic, gallic, and protocatechuic acids made up 60 to 80% of the identified free‐acid content of six litter leachates. Significant correlation was obtained between total free‐organic acid content and dissolved Al (r = 0.87, p < 0.001) and Fe (r = 0.82, p < 0.001) from soils.

Study of interactions between relevant organic acids and aluminium in model solutions using HPLC and IC

“…Thus, we can conclude that the determination of free oxalic acid under such conditions was not possible due to the presence of stable Al complexes co-eluting with it. Similar problems were reported by Hue et al (1986), Fox et al (1990), and Pohlman and McColl (1988). They used ion exclusion chromatography columns in combination with UV detection.…”

Formas de carbono em Latossolo Vermelho Eutroférrico sob plantio direto no sistema biogeográfico do cerrado

“…Contrastes entre plantio direto irrigado (PI) e plantio direto de sequeiro (PS) para carbono orgânico total (CT), carbono mineralizável (CM) e carbono da biomassa microbiana (CB) em agregados maiores e menores que 0,25 mm, respectivamente (1 e 2), de um Latossolo Vermelho Eutroférrico Típico, em cinco profundidades NS, °, * e **: não-significativo e significativo a 10, 5 e 1 %, respectivamente. (Pohlman & Mccoll, 1988). Assim, os maiores índices de CS encontrados no solo sob floresta nativa se devem, provavelmente, ao maior incremento e à qualidade das substâncias orgânicas no ambiente natural.…”

Resíduos de plantas de cobertura e mobilidade dos produtos da dissolução do calcário aplicado na superfície do solo

“…A identificação de ácidos orgânicos de baixo peso molecular na solução de solo tem sido efetuada em solos de clima temperado (Hue et al, 1986;Pohlman & McColl, 1988;Bissani, 2000). Nas condições de clima e solo do Sul do Brasil, a identificação desses compostos na solução do solo não tem sido bemsucedida (Miyazawa et al, 1992).…”