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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

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Resource Level Coverage

Spatial

Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
Place/Area Name:
Luquillo Experimental Forest
North Latitude
18.3223°
East Longitude
-65.7407°
South Latitude
18.2614°
West Longitude
-65.8569°

Temporal

Start Date:
End Date:

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

Hall, S., A. A. Berhe, A. Thompson (2020). LCZO -- Soil Biogeochemistry -- Order from disorder: do soil organic matter composition and turnover co-vary with iron phase crystallinity? -- Northeastern Puerto Rico -- (2016-2018), HydroShare, http://www.hydroshare.org/resource/ffb66a2c60f34eeab2af7abd660bb81c

This resource is shared under the Creative Commons Attribution CC BY.

 http://creativecommons.org/licenses/by/4.0/
CC-BY

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