Abstract
This study used a combined tracer approach of isotopically labelled carbon (C) and rare earth oxides (REO) to
determine soil aggregate transfer paths following input of organic matter. A model quantifying aggregate
turnover rates over time was verified by a controlled incubation study. Four natural soil aggregate size ranges
(<0.053 mm, 0.053-0.25 mm, 0.25-2 mm and 2-5 mm) were labelled with different REO tracers and packed to
form a composite soil sample. The organic input was 1 mg 13C g-1 soil of 13C-labelled glucose. There were
four treatments: i) soil without REO and 13C as a control, ii) soil labelled with REO, iii) soil without REO but
amended with 13C-glucose, and iv) soil labelled with REO and amended with 13C-glucose. Aggregate stability,
REO concentrations, soil respiration and 13C were measured after 0, 7, 14 and 28 days incubation. REOs were
found to not impact microbial activity (P > 0.05). Based on the 84%-106% recovery of REOs after wet sieving
of aggregates, and a close 1:1 relationship between measured aggregates and model predictions, REOs were
found to be an effective tracer for studies of aggregate dynamics. A greater portion of aggregates transferred
between neighbouring size fractions. The turnover rate was faster for macroaggregates than for
microaggregates, and slowed down over the incubation time. The new C was accumulated more but
decomposed faster in macroaggregates than in microaggregates. A positive relationship was observed
between the 13C concentration in aggregates and the aggregate turnover rate (P < 0.05). The relative change
in each aggregate fraction generally followed an exponential growth over time in the formation direction and
an exponential decay in the breakdown direction. We proposed a first order kinetic model for aggregate
dynamics which can separate aggregate formation, stabilization and breakdown processes. This study
demonstrates that REOs can track aggregate life cycles and provide unique and important information about
the relationship between C cycling and aggregate turnover.
Original language | English |
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Pages (from-to) | 81-94 |
Number of pages | 14 |
Journal | Soil Biology and Biochemistry |
Volume | 109 |
Early online date | 16 Feb 2017 |
DOIs | |
Publication status | Published - Jun 2017 |
Bibliographical note
This work was granted by the China-UK jointed Red Soil Critical Zone project from National Natural Science Foundation of China (NSFC: 41571130053, 41371235) and from Natural Environmental Research Council (NERC: Code: NE/N007611/1).Keywords
- aggregate turnover
- modelling
- organic amendment
- rare earth oxide
- soil aggregation
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Paul Hallett
- Biological Sciences, Aberdeen Centre For Environmental Sustainability - Chair in Soil Physics
Person: Academic