Abstract
The principle of enzyme kinetics suggests that the temperature sensitivity (Q 10) of soil organic matter (SOM) decomposition is inversely related to organic carbon (C) quality, i.e., the C quality-temperature (CQT) hypothesis. We tested this hypothesis by performing laboratory incubation experiments with bulk soil, macroaggregates (MA, 250–2000 μm), microaggregates (MI, 53–250 μm), and mineral fractions (MF, <53 μm) collected from an Inner Mongolian temperate grassland. The results showed that temperature and aggregate size significantly affected on SOM decomposition, with notable interactive effects (P<0.0001). For 2 weeks, the decomposition rates of bulk soil and soil aggregates increased with increasing incubation temperature in the following order: MA>MF>bulk soil >MI(P <0.05). The Q 10 values were highest for MA, followed (in decreasing order) by bulk soil, MF, and MI. Similarly, the activation energies (Ea) for MA, bulk soil, MF, and MI were 48.47, 33.26, 27.01, and 23.18 KJ mol−1, respectively. The observed significant negative correlations between Q 10 and C quality index in bulk soil and soil aggregates (P<0.05) suggested that the CQT hypothesis is applicable to soil aggregates. Cumulative C emission differed significantly among aggregate size classes (P <0.0001), with the largest values occurring in MA (1101 μg g−1), followed by MF (976 μg g−1) and MI (879 μg g−1). These findings suggest that feedback from SOM decomposition in response to changing temperature is closely associated withsoil aggregation and highlights the complex responses of ecosystem C budgets to future warming scenarios.
Highlights
Soil aggregates play important roles in maintaining soil structure, fertility, and stability, and in influencing the decomposition dynamics of soil organic matter (SOM) [1,2,3]
The main objectives of this study were to investigate (i) how decomposition of SOM varies among aggregate size and temperature; (ii) how Q10 values differ among soil aggregates; and (iii) whether C quality-temperature (CQT) hypothesis is appropriate for soil aggregates
The decomposition rate of SOM still varied among soil aggregates.Some studies have found that SOM decomposition rates generally decrease with decreasing aggregate size [3,24], and that MA contains a greater proportion of decomposable C than whole soil [25]
Summary
Soil aggregates play important roles in maintaining soil structure, fertility, and stability, and in influencing the decomposition dynamics of soil organic matter (SOM) [1,2,3]. Soil aggregates store large quantities of SOM [1,2], and the distribution of SOM within aggregates is PLOS ONE | DOI:10.1371/journal.pone.0117033. SOM Decomposition and Temperature Sensitivity in Soil Aggregates Soil aggregates store large quantities of SOM [1,2], and the distribution of SOM within aggregates is PLOS ONE | DOI:10.1371/journal.pone.0117033 February 18, 2015
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