Reduced Organic Carbon Content during the Evolvement of Calcareous Soils in Karst Region

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).

Conversion of farmland to forest or grassland improved soil C, N and multi-functionality in a subtropical karst region, southwest China

“…1a,b). These ndings suggest that during the recovery process, afforestation land and abandonment land are more conducive to SOC accumulation compared to grassland models 24,25 .…”

Microbial Communities and Soil Respiration during Rice Growth in Paddy Fields from Karst and Non-Karst Areas

“…SOC played an important pole in shaping the pattern of soil bacteria and fungi community structures [25], which indicated that increasing biomasses of root and litter stimulated microbial growth in KA [26]. In addition, bacterial and fungal populations are able to increase the stability of calcareous SOC [27] that might reduce the decomposition of soil organic matter. For example, Flavobacterium and Lysobacter dominated the karst area communities and exhibited relative abundances of 1.24-14.73%,which Flavobacterium can decompose organic matter and Lysobacter can synthesize organic matter using CO 2 as a carbon source [25].…”

Soil Organic Carbon Distribution and Its Response to Soil Erosion Based on EEM-PARAFAC and Stable Carbon Isotope, a Field Study in the Rocky Desertification Control of South China Karst

“…Carbon sinks in karst regions around the world account for more than one-third of the global "missing sinks" [17,18]. According to zoning calculation, carbon sinks in karst regions in China amount to 36,991 million tons [19], making it significant for improving ecological carbon sink capacity [20]. The soil habitat in karst areas is fragile and susceptible to erosion.…”