Abstract
BackgroundRevealing the variations in soil aggregate-related organic carbon (OC) and labile organic carbon (LOC) fractions in a chronosequence of Chinese fir plantations plays an important role in better understanding the impact of soil carbon sink or source on the Chinese fir plantation ecosystem. In this study, soil samples in a depth of 0–20 cm were collected from Chinese fir plantations at different stand ages (0, 9, 17, and 26 years old) in Guangxi, China. With the optimal moisture sieving method adopted, the soil aggregates of 4 different sizes were obtained, including > 2-mm, 2–1-mm, 1–0.25-mm, and < 0.25-mm aggregates. Soil OC and LOC fractions were measured in the aggregates of different sizes. The LOC fractions included readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC).ResultsSoil aggregate stability, as indicated by the mean weight diameter (MWD), was the highest in the 17-year-old Chinese fir plantations and was significantly positively related (p < 0.05) to the concentrations of OC and LOC fractions (except for the ROC and MOC), with the POC in particular. As for all stand ages of Chinese fir plantations, the concentrations of soil OC and LOC fractions were significantly increased as the aggregate size decreased. Consequently, there were more OC and LOC fractions distributed in the < 0.25-mm aggregates. During the stand development, the concentrations of soil OC and LOC fractions first increased and then decreased, with the highest levels detected in the 17-year-old Chinese fir plantations, indicating that the 17-year-old Chinese fir plantations were conducive to the accumulation of soil OC and LOC fractions.ConclusionAfter 17 years of planting, promoted soil carbon (especially for the POC) accumulation contributes significantly to enhancing soil aggregate stability for the Chinese fir plantations in Guangxi, China.
Highlights
Over the last century, extensive deforestation and longterm tillage have resulted in land degradation given the sharp rise in population pressure across China
The peak of soil aggregate stability appeared in the 17-year-old fir plantations, which is suspected to result from the accumulation of soil organic carbon (OC) and labile organic carbon (LOC) fractions in these fir plantations
The correlation between soil aggregate stability and LOC fraction concentrations was tested, and the results showed that aggregate stability was positively correlated with particulate organic carbon (POC), microbial biomass carbon (MBC), and water-soluble organic carbon (WOC) concentrations in bulk soil to a significant extent (Fig. 3c–e), implying that soil aggregate stability was largely affected by
Summary
Extensive deforestation and longterm tillage have resulted in land degradation given the sharp rise in population pressure across China. As the active parts of soil OC, labile organic carbon (LOC) fractions, including readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC), are possibly more sensitive to the conversion of land use than soil OC (Sheng et al 2015). WOC consists of various soluble organic residues and is regarded as the least stable fraction of soil OC (Schnabel et al 2002). MOC comprises small molecular weight compounds resulting from microbial processing and is prone to the decomposition by soil microorganisms (Zhao et al 2008). Soil OC and LOC fractions were measured in the aggregates of different sizes. The LOC fractions included readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC)
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