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| Titel |
Influence of pore structure on carbon retention/loss in soil
macro-aggregates |
| VerfasserIn |
Michelle Quigley, Alexandra Kravchenko, Mark Rivers |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147066
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| Publikation (Nr.) |
 EGU/EGU2017-11166.pdf |
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| Zusammenfassung |
| Carbon protection within soil macro-aggregates is an important component of soil carbon
sequestration. Pores, as the transportation network for microorganisms, water, air and
nutrients within macro-aggregates, are among the factors controlling carbon protection
through restricting physical accessibility of carbon to microorganisms. The understanding of
how the intra-aggregate pore structure relates to the degree of carbon physical protection,
however, is currently lacking. This knowledge gap can lead to potentially inaccurate
models and predictions of soil carbon’s fate and storage in future changing climates.
This study utilized the natural isotopic difference between C3 and C4 plants to
trace the location of newly added carbon within macro-aggregates before and after
decomposition and explored how location of this carbon relates to characteristics
of intra-aggregate pores. To mimic the effect of decomposition, aggregates were
incubated at 23˚ C for 28 days. Computed micro-tomographic images were used
to determine pore characteristics at 6 μm resolution before and after incubation.
Soil (0-10 cm depth) from a 20 year continuous corn (C4 plant) experiment was
used. Two soil treatments were considered: 1) “destroyed-structure”, where 1 mm
sieved soil was used and 2) “intact-structure”, where intact blocks of soil were used.
Cereal rye (Secale cereale L.) (C3 plant) was grown in the planting boxes (2 intact, 3
destroyed, and one control) for three months in a greenhouse. From each box, ∼5
macro-aggregates of ∼5 mm size were collected for a total of 27 macro-aggregates. Half of
the aggregates were cut into 5-11 sections, with relative positions of the sections within
the aggregate recorded, and analyzed for δ13C. The remaining aggregates were
incubated and then subjected to cutting and δ13C analysis. While there were no
significant differences between the aggregate pore size distributions of the two
treatments, the roles that specific pores sizes played in carbon protect were disparate. In
intact-structure aggregates, prior to incubation, there was no association between carbon
distribution and pores. After incubation, significant correlations (α=0.05) were
observed between abundance of 6-40 μm pores and both soil organic carbon (SOC) and
δ13C. Sections containing more 6-40 μm pores also had increased amounts of SOC
(r2=0.23) with higher presence of C4 carbon (r2=0.27). This indicates preferential
preservation of older carbon in the pores of this size range. Prior to incubation,
destroyed-structure aggregates had higher amounts of C3 carbon associated with 40-95 μm
pores (r2=0.14), pointing to a greater presence of newly added carbon within these pores.
However, after incubation there was a significant loss of SOC from these pores
(r2=0.22) and, specifically, the loss of C3 carbon (r2=0.16). In the studied soil,
pores of 6-40 μm size range appeared to control the preservation of older carbon,
while 40-95 μm pores controlled the fate of newly added carbon. Older carbon
preservation in 6-40 μm pores was mostly observed in macro-aggregates from the soil
with intact structure, while the associations between 40-95 μm pores and gains and
losses of newly added carbon were primarily observed in the macro-aggregates
that were formed anew in the sieved soil during the plant growing experiment. |
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