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LCZO -- Soil Biogeochemistry -- Order from disorder: do soil organic matter composition and turnover co-vary with iron phase crystallinity? -- Northeastern Puerto Rico -- (2016-2018)
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Abstract
Soil organic matter (SOM) often increases with the abundance of short-range-ordered iron (SRO Fe) mineral phases at local to global scales, implying a protective role for SRO Fe. However, less is known about how Fe phase composition and crystal order relate to SOM composition and turnover, which could be linked to redox alteration of Fe phases. We tested the hypothesis that the composition and turnover of mineral-associated SOM co-varied with Fe phase crystallinity and abundance across a well-characterized catena in the Luquillo Experimental Forest, Puerto Rico, using dense fractions from 30 A and B horizon soil samples. The d13C and d15N values of dense fractions were strongly and positively correlated (R2 = 0.75), indicating microbial transformation of plant residues with lower d13C and d15N values. However, comparisons of dense fraction isotope ratios with roots and particulate matter suggested a greater contribution of plant versus microbial biomass to dense fraction SOM in valleys than ridges. Similarly, diffuse reflectance infrared Fourier transform spectroscopy indicated that SOM functional groups varied significantly along the catena. These trends in dense fraction SOM composition, as well as D14C values indicative of turnover rates, were significantly related to Fe phase crystallinity and abundance quantified with selective extractions. Mo¨ssbauer spectroscopy conducted on independent bulk soil samples indicated that nanoscale ordered Fe oxyhydroxide phases (nanogoethite, ferrihydrite, and/or very-SRO Fe with high substitutions) dominated (66–94%) total Fe at all positions and depths, with minor additional contributions from hematite, silicate and adsorbed FeII, and ilmenite. An additional phase that could represent organic-FeIII complexes or aluminosilicate-bearing FeIII was most abundant in valley soils (17–26% of total Fe). Overall, dense fraction samples with increasingly disordered Fe phases were significantly associated with increasingly plant-derived and fastercycling SOM, while samples with relatively morecrystalline Fe phases tended towards slower-cycling SOM with a greater microbial component. Our data suggest that counter to prevailing thought, increased SRO Fe phase abundance in dynamic redox environments could facilitate transient accumulation of litter derivatives while not necessarily promoting long-term C stabilization.
publication can be found here https://doi.org/10.1007/s10533-018-0476-4
Subject Keywords
Coverage
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Temporal
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Content
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LCZO -- Soil Biogeochemistry -- soil organic matter; Iron phase crystallinity -- Northeastern Puerto Rico -- (2016-2018)
OVERVIEW
Description/Abstract
Soil organic matter (SOM) often increases with the abundance of short-range-ordered iron (SRO Fe) mineral phases at local to global scales, implying a protective role for SRO Fe. However, less is known about how Fe phase composition and crystal order relate to SOM composition and turnover, which could be linked to redox alteration of Fe phases. We tested the hypothesis that the composition and turnover of mineral-associated SOM co-varied with Fe phase crystallinity and abundance across a well-characterized catena in the Luquillo Experimental Forest, Puerto Rico, using dense fractions from 30 A and B horizon soil samples. The d13C and d15N values of dense fractions were strongly and positively correlated (R2 = 0.75), indicating microbial transformation of plant residues with lower d13C and d15N values. However, comparisons of dense fraction isotope ratios with roots and particulate matter suggested a greater contribution of plant versus microbial biomass to dense fraction SOM in valleys than ridges. Similarly, diffuse reflectance infrared Fourier transform spectroscopy indicated that SOM functional groups varied significantly along the catena. These trends in dense fraction SOM composition, as well as D14C values indicative of turnover rates, were significantly related to Fe phase crystallinity and abundance quantified with selective extractions. Mo¨ssbauer spectroscopy conducted on independent bulk soil samples indicated that nanoscale ordered Fe oxyhydroxide phases (nanogoethite, ferrihydrite, and/or very-SRO Fe with high substitutions) dominated (66–94%) total Fe at all positions and depths, with minor additional contributions from hematite, silicate and adsorbed FeII, and ilmenite. An additional phase that could represent organic-FeIII complexes or aluminosilicate-bearing FeIII was most abundant in valley soils (17–26% of total Fe). Overall, dense fraction samples with increasingly disordered Fe phases were significantly associated with increasingly plant-derived and fastercycling SOM, while samples with relatively morecrystalline Fe phases tended towards slower-cycling SOM with a greater microbial component. Our data suggest that counter to prevailing thought, increased SRO Fe phase abundance in dynamic redox environments could facilitate transient accumulation of litter derivatives while not necessarily promoting long-term C stabilization.
Creator/Author
Steven J. Hall|Asmeret A. Berhe|Aaron Thompson
CZOs
Luquillo
Contact
Miguel Leon leonmi@sas.upenn.edu
Subtitle
do soil organic matter composition and turnover co-vary with iron phase crystallinity?
SUBJECTS
Disciplines
Biogeochemistry
Topics
Soil Biogeochemistry
Subtopic
soil organic matter; Iron phase crystallinity
Keywords
Radiocarbon|FTIR|Mossbauer|Nitrogen isotope|Carbon isotope|Redox
Variables
Free light fraction percent N Free light fraction percent C Free light fraction C:N ratio Free light fraction C stable isotope composition|per mil relative to VPDB Free light fraction N stable isotope composition|per mil relative to N2 Occluded light fraction percent N Occluded light fraction percent C Occluded light fraction C:N ratio Occluded light fraction C stable isotope composition|per mil relative to VPDB Occluded light fraction N stable isotope composition|per mil relative to N2 Dense fraction percent N Dense fraction percent C Dense fraction C:N ratio Dense fraction C stable isotope composition|per mil relative to VPDB Dense fraction N stable isotope composition|per mil relative to N2 Dense fraction 14C composition|capital delta notation Dense fraction Fe measured in acid ammonium oxalate extraction|mg Fe per gram dry soil Dense fraction Fe measured in citrate-dithionite extraction|mg Fe per gram dry soil
Variables ODM2
Iron|Chlorophyll c|Magnesium|Carbon-14|Carbon to nitrogen mass ratio|Carbon-13, stable isotope ratio delta|Soil Organic matter (SOM) density fractionation
TEMPORAL
Date Start
2016-01-01
Date End
2018-01-01
SPATIAL
Field Areas
Northeastern Puerto Rico and the Luquillo Mountains
Location
Northeastern Puerto Rico
North latitude
18.32232903
South latitude
18.26143335
West longitude
-65.85692813
East longitude
-65.7407
REFERENCE
Citation
Hall, S.J., Berhe, A.A. & Thompson, A. Biogeochemistry (2018). https://doi.org/10.1007/s10533-018-0476-4
CZO ID
6795
Additional Metadata
| Name | Value |
|---|---|
| czos | Luquillo |
| czo_id | 6795 |
| citation | Hall, S.J., Berhe, A.A. & Thompson, A. Biogeochemistry (2018). https://doi.org/10.1007/s10533-018-0476-4 |
| keywords | Radiocarbon, FTIR, Mossbauer, Nitrogen isotope, Carbon isotope, Redox |
| subtitle | do soil organic matter composition and turnover co-vary with iron phase crystallinity? |
| variables | Free light fraction percent N Free light fraction percent C Free light fraction C:N ratio Free light fraction C stable isotope composition, per mil relative to VPDB Free light fraction N stable isotope composition, per mil relative to N2 Occluded light fraction percent N Occluded light fraction percent C Occluded light fraction C:N ratio Occluded light fraction C stable isotope composition, per mil relative to VPDB Occluded light fraction N stable isotope composition, per mil relative to N2 Dense fraction percent N Dense fraction percent C Dense fraction C:N ratio Dense fraction C stable isotope composition, per mil relative to VPDB Dense fraction N stable isotope composition, per mil relative to N2 Dense fraction 14C composition, capital delta notation Dense fraction Fe measured in acid ammonium oxalate extraction, mg Fe per gram dry soil Dense fraction Fe measured in citrate-dithionite extraction, mg Fe per gram dry soil |
| disciplines | Biogeochemistry |
Credits
Funding Agencies
This resource was created using funding from the following sources:
| Agency Name | Award Title | Award Number |
|---|---|---|
| NSF DEB | 1457805 | |
| NSF EAR | Luquillo Critical Zone Observatory | 1331841 |
How to Cite
This resource is shared under the Creative Commons Attribution CC BY.
http://creativecommons.org/licenses/by/4.0/
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