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As the interface between plants and soil, the organic horizon is the foundation of forest ecosystems. Two potential predictors of O-layer properties, vegetation and mineral soil type, are difficult to separate because they typically covary. We conducted a factorial study involving four canopy tree species and two soil types with distinctly different hydrology and topographic position to parse patterns in chemistry and microbiota of the O-layer in a north-temperate deciduous forest. There were frequent strong effects of tree species. White ash frequently differed from the other trees: e.g., lower cation exchange capacity and exchangeable acidity, thinner Oi layer, lower %C and C:N, and, from phospholipid fatty acids, more AM fungi and less gram+ bacteria. These patterns, presumably due to species-specific attributes of leaf litter quality, root exudates, and microbial associations, must arise over decades, given that the stands in the study age between 85 and 100 years. We also found patterns in the O-layer related to underlying soil type, independent of tree species: e.g., Bh podzols, compared to Typical podzols, had higher trace metals, thicker Oa layer, and more AM fungi. Relations between mineral soil type and the organic layer, which were larger than expected, could arise because landscape features that influence hydrology and therefore soil formation over millennia also influence biogeochemistry of the organic layer over decades. It could also involve bioturbation by organisms across horizons. There is basic and applied value in models that can predict properties of the O-layer based on vegetation and soil types.
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This content will become publicly available on December 8, 2026
Relations of the O-horizon with canopy tree species and hydropedologic soil types
As the interface between plants and soil, the organic horizon is the foundation of forest ecosystems. Two potential predictors of O-horizon properties, vegetation and mineral soil type, are difficult to separate because they typically covary. We conducted a factorial study involving four canopy tree species and two soil types with different hydrology and topographic position to parse patterns in chemistry and microbiota of the O-horizon in a north-temperate deciduous forest. There were frequent strong effects of tree species. Organic horizon properties under white ash frequently differed from the other trees: e.g., lower cation exchange capacity and exchangeable acidity, thinner Oi horizon, lower %C and C:N, and, from phospholipid fatty acids, more AM fungi and less gram positive bacteria. These patterns, presumably due to species-specific attributes of leaf litter quality, root exudates, and microbial associations, must arise over decades, given that the forest stands that we studied were established only 85—100 years ago. We also found patterns in the O-horizon related to underlying soil type, independent of tree species: e.g., Bh podzols, compared to typical podzols, had higher trace metals, thicker Oa horizon, and more AM fungi. Relationships between mineral soil type and the organic horizon could arise because landscape features that influence hydrology and therefore soil formation over centuries also influence biogeochemistry of the organic horizon over decades. It could also involve bioturbation by organisms across horizons. There is basic and applied value in better understanding of properties of the O-horizon based on vegetation and soil types.
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- Award ID(s):
- 2224545
- PAR ID:
- 10659313
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Biogeochemistry
- Volume:
- 169
- Issue:
- 1
- ISSN:
- 1573-515X
- Subject(s) / Keyword(s):
- Ash trees Fraxinus Hydropedology O-horizon Soil chemistry
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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