Open AccessCarbon delivery to deep mineral horizons in Hawaiian rain forest soils
Author(s) -
MarinSpiotta Erika,
Chadwick Oliver A.,
Kramer Marc,
Carbone Mariah S.
Publication year - 2011
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jg001587
Subject(s) - soil water , ammonium oxalate , subsoil , organic matter , environmental chemistry , total organic carbon , geology , podzol , dissolved organic carbon , soil horizon , soil organic matter , soil science , geochemistry , mineralogy , chemistry , inorganic chemistry , organic chemistry
This study aimed to better understand the mechanisms for soil organic matter delivery to and accumulation in mineral horizons of tropical rain forest, volcanic soils. We used soil morphology, lysimetry, isotopes, and spectroscopy to investigate the role of preferential flow paths in the delivery of carbon (C) to the subsoil. High rainfall, high primary productivity, and the dominance of highly reactive, short‐range‐order minerals combine to sequester substantial stocks of soil C with long mean residence times. The soils have large peds, separated by wide cracks, which form a network of channels propagating downward through the top 40 to 60 cm, facilitating macropore flow. The channel infillings and crack surfaces were enriched in organic material (OM) with lower C:N ratios, and had higher ammonium oxalate‐extractable Al, and lower ammonium oxalate‐extractable Fe than the adjacent mineral bulk soil. CP MAS 13 C‐NMR spectra of OM accumulating at depth showed strong signal intensities in the carboxyl and carbonyl C regions, indicative of organic acids, while decaying roots showed greater contributions of aromatic and O‐alkyl C. The ratios of alkyl‐to‐O‐alkyl C in the organic infillings were more similar to those of the bulk Bh and to dissolved organic matter than to those of decaying roots. Radiocarbon‐based ages of OM infillings at >50 cm depth were significantly younger than the mineral soil (2000 years versus 7000 years). Respired CO 2 from incubated soils showed that OM accumulating at depth is a mixture of modern and much older C, providing further evidence for the downward movement of fresh C.