Abstract
Understanding the changes in soil organic carbon (SOC) storage is important for accurately predicting ecosystem C sequestration and/or potential C losses, but the relevant information, especially for the evolvement of calcareous soil is limited in karst regions. Three calcareous soils with different evolvement intensities were sampled from an evergreen broadleaved forest in the subtropical region of southwest of China to investigate the changes in different SOC fractions and microbial communities. The results showed that: (1) The contents of SOC, dissolved organic carbon (DOC), mineral protected organic carbon (MOC), and recalcitrant organic carbon (ROC) significantly decreased with increasing evolvement intensity of calcareous soil, but pH and the chemical composition of SOC, including Alkyl C, O-alkyl C, Aromatic C, and Carbonyl C, did not significantly change, suggesting that various SOC fractions synergistically decrease with the evolvement of calcareous soil. (2) The evolvement of calcareous soil had a substantial negative effect on total phospholipid fatty acids (PLFA), bacteria (i.e., Gram positive bacteria and Gram negative bacteria), fungi, and actinomycetes, but did not affect the ratio of fungi to bacteria. This result supported the conclusion that various SOC fractions were synchronously loss with the evolvement of calcareous soil. (3) Results from the multivariate statistical analysis showed a significant correlation between SOC fractions (including SOC, DOC, MOC, and ROC) and soil base cations, mainly calcium (Ca), iron (Fe), and aluminum (Al). This strengthens the fact that SOC stability largely depends on the complex relationship between organic matter and mineral composition in soil. Taken together, the reduction of SOC during the evolvement of soil in the karst areas accords with some mechanisms of previous studies (e.g., microbial composition and soil geochemistry), and also has its own unique characteristics (e.g., the relative contribution of carbons to chemical shift regions of CPMAS 13C-NMR spectra and F:B ratio).
Highlights
Soil organic matter (SOM) is the core of soil quality, which is important to soil fertility, sustainable agricultural systems, climate change, and many other factors related to the survival and development of the earth and human beings [1]
We explored the responses of soil chemistry, microbial community as assessed by phospholipid fatty acid (PLFA) analysis, and C stock in three soil fractions, including dissolved organic carbon (DOC), mineral protected organic carbon (MOC), and recalcitrant organic carbon (ROC)
The SiO2 /Al2 O3 ratio (Sa) and SiO2 /(Al2 O3 + Fe2 O3 ) ratio (Saf) in soil decreased significantly, while Fed/Fet increased significantly as black calcareous soil (BLCS) evolved to red calcareous soil (RCS)
Summary
Soil organic matter (SOM) is the core of soil quality, which is important to soil fertility, sustainable agricultural systems, climate change, and many other factors related to the survival and development of the earth and human beings [1]. Soils store climatically significant amounts of carbon (C) as SOM, which is about 2.3 times and 3.5 times greater than that in atmospheric CO2 and all living terrestrial plants [2]. SOM decomposition is one of the key ways for soil to release CO2 into the atmosphere, and it has a significant impact on global climate change. Considering the role of soil organic carbon (SOC) storage, many soil types such as Cambosols [5], permafrost soil [4], and Oxisols [6] have been widely investigated. These studies were mainly conducted in non-karst regions, but the relevant studies are limited in karst regions
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