Soil Carbon Aggregate Dynamics

The distribution of 13C-glucose in soil aggregate fractions during incubation. Different lowercase letters denote significant differences at P < 0.05 between sampling dates under the same treatment, and different captical letters denote significant differences at P < 0.05 between treatments on the same sampling date.

Soil aggregate dynamics involves aggregate formation, stabilization and breakdown processes, largely controlled by biological processes in soil and their interaction with physical processes such as wetting/drying, thawing/freezing, and tillage. Although considerable research has explored soil aggregate dynamics, the life cycle of an aggregate and its impact on microbial mediated C cycling remains elusive.

New short-term aggregate dynamics research[1] has found

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.

Greater 13C concentration in 2–5 mm and 0.25–2 mm fractions compared to the <0.25 mm fraction indicates that the new C was more readily accumulated in macroaggregates than in microaggregates. This is likely due to the rate of glucose movement into macroaggregates through large pores that are available in comparison to microaggregates.

The negative values of the relative change in 2–5 mm aggregates over time with or without 13C-glucose addition in the breakdown direction indicates progressively less breakdown and hence stabilization of this fraction compared to the initial condition.

The new C input decreased the breakdown of all sizes of aggregates and increased their formation rate.

In the formation direction, the newly formed aggregates exponentially increased with time, with larger aggregates forming faster than smaller ones.

The aggregate stability increased greatly immediately after C input as glucose and then slowed down with the further decomposition of this added substrate.

[1] Combined turnover of carbon and soil aggregates using rare earth oxides and isotopically labelled carbon as tracers


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