Abstract
Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle. In this study, the seasonal fluctuations in LOC, the activities of carbon-cycle related enzymes, and the bacterial and fungal communities were analyzed for soils collected from two forests, namely Betula albosinensis (Ba) and Picea asperata Mast. (Pa), in the Qinling Mountains of China. Results revealed that the seasonal average contents of microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), and dissolved organic carbon (DOC) of Pa forest soil were 13.5%, 30.0% and 15.7% less than those in Ba soil. The seasonal average enzyme activities of β-1,4-glucosidase (βG), and β-1,4-xylosidase (βX) of Ba forest soils were 30.0% and 32.3% higher than those of Pa soil while the enzyme activity of cellobiohydrolase (CBH) was 19.7% lower. Furthermore, the relative abundance of Acidobacteria was significantly higher in summer than in winter, whereas the relative abundance of Bacteroidetes was higher in winter. Regarding the fungal communities, the relative abundance of Basidiomycota was lowest in winter, whereas Ascomycota predominated in the same season. In addition, the soil LOC was significantly positively correlated with the CBH, βG and βX activities. Changes in LOC were significantly correlated with Acidobacteria, Bacteroidetes and Basidiomycota. We conclude that the seasonal fluctuations in forest soil LOC fractions relied on carbon cycle-associated enzymatic activities and microorganisms, which in turn were affected by climatic conditions.
Highlights
Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle
The presence of significant positive correlations between Acidobacteria and easily oxidized organic carbon (EOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in this study indicated that Acidobacteria promoted LOC formation via their metabolic processes
Compared with Betula albosinensis (Ba) forest soil, Picea asperata Mast. (Pa) soil was featured with lower contents of soil organic carbon (SOC), MBC, EOC and lower activities of βG and βX, which were mainly attributable to the differences in litterfall and root exudates of coniferous forest (Pa) and broadleaf forest (Ba)
Summary
Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle. We conclude that the seasonal fluctuations in forest soil LOC fractions relied on carbon cycle-associated enzymatic activities and microorganisms, which in turn were affected by climatic conditions. Soil microbial communities and enzymatic activities are affected by season alternation. Season change can affect the types and amount of soil organic matter by regulating the growth and photosynthesis of trees[21], thereby affecting the soil microbial composition and enzymatic activities. Soil microbial communities are affected by other seasonal climatic factors, such as temperature and h umidity[22,23]. Changes in season and climatic factors are of significant importance, which directly or indirectly affect soil microbial communities and enzymatic activities. The controlling factors might differ in different systems; no consistent conclusions have been drawn and requiring more investigation
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