Interactions of soil particulate organic matter chemistry and microbial community composition mediating carbon mineralization in karst soils

Abstract

Particulate organic matter (POM) chemistry and microbial degraders are important determinants of soil carbon (C) mineralization, but the effects of their interactions on C mineralization are largely unknown. Two contrasting soils with different POM chemical composition from karst ecosystems were sampled, sterilized, and cross-inoculated with microorganisms for 124 days to explore the relationships between POM chemical composition, microbial community composition, and soil organic C (SOC) mineralization. Pyrolysis-gas chromatography/mass spectrometry analysis was used to determine POM chemistry, and phospholipid fatty acid (PLFA) analysis was used to characterize the soil microbial community. Microbial cross-inoculation showed that the microbial community composition did not change in response to changes in soil C and that the relatively labile POM components, e.g., fatty acids and n-alkenes, explained 61.2% of the variation in microbial community composition. Microbial community composition, such as PLFAs cy19:0, i17:0, 10Me16:0, and 18:2ω6,9c, strongly influenced POM chemical composition, explained 94.5% of the variation in POM chemical composition. These results indicated that soil microbial communities could adapt to changes in POM and served as main drivers of POM chemistry alterations. In addition, mineralized soil C (% of SOC) was significantly influenced by microbial community composition, soil source, and their interactions. Redundancy analysis and Mantel tests further revealed that SOC mineralization was strongly affected by POM chemical composition (e.g., the content of ketones and p-hydroxyphenyl) and microbial community composition (e.g., the content of PLFAs 16:1ω7c and 10Me16:0), and that the influence of microbial community composition on SOC mineralization was highly dependent on POM chemical composition, suggesting that the interactions of POM chemistry and microbial community composition mediate SOC mineralization. These analyses indicate a tight relationship between POM chemistry and microbial community composition, and highlight the importance of their interactions in mediating the persistence of organic matter in karst soils.