Abstract
Low molecular weight organic carbon (LMWOC) can be physiochemically protected by soil particles via sorption and enfolding. Soil management usually changed the soil particle distribution (e.g. upland vs paddy soil). Higher organic carbon stocks in paddy soil than upland soil could partially be because of the greater immobilization and inaccessibility of LMWOC in paddy soil. To assess the effects of soil management and types of LMWOC on its carbon stabilization in soil density fractions, a simulated study was conducted to investigate the distribution of LMWOC (i.e., glucose, acetic acid, and oxalic acid) in soil density fractions based on 13C-labeling experiments in both soils. The results showed that the total 13C recovery was determined by LMWOC types, following the order of glucose> acetic acid > oxalic acid (p < 0.05). Both soil management and types of LMWOC significantly affect carbon distribution in soil density fractions. The 13C from LMWOC was predominant in the 1.85–2.4 g.cm−3 fraction of upland soil, while the highest concentration of LMWOC 13C was found in mineral grains (2.4–2.65 g.cm−3) in paddy soil, suggesting that more LMWOC was preserved in high density fractions in paddy soil than in upland soil. Our results highlighted that the LMWOC was mainly associated with aggregates in upland soil while subjected to mineral adsorption in paddy soil.
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