Biomarkers evidence shows a preferential occlusion of microbial necromass in mineral-associated and not particle organic matter

Abstract

Increasing experimental evidence and modeling efforts have found that microbial necromass is highly associated with mineral-associated organic matter (MAOM). However, recent studies found that MAOM is predominantly derived from plant litter materials, challenging the notion that microbial necromass is preferentially occluded in MAOM. Here, we compiled 245 observations of glucosamine, galactosamine, mannosamine and muramic acid (specific biomarker for microbial necromass) in MAOM and particle organic matter (POM) from current experiments conducted in croplands, forests and grasslands. We evaluated the influence of climatic and edaphic factors on the partitioning of amino sugars in MAOM and POM. Total amino sugars are predominantly occluded within MAOM (3.23 ± 0.53 mg/g soil) rather than POM (1.73 ± 0.26 mg/g soil) on a global scale, and this preference varies among ecosystem types. Specifically, there are no significant differences in the concentrations of total amino sugars between MAOM and POM in croplands and grasslands. However, forests have significantly higher concentrations of total amino sugars in MAOM (3.88 ± 0.85 mg/g soil) compared to POM (2.23 ± 0.57 mg/g soil). Our results corroborate a consistent preponderance of glucosamine over muramic acid in MAOM and POM across diverse ecosystems. Altitude and MAT were key factors in explaining the occlusion of total amino sugars in MAOM, but those in POM decreased with increasing soil bulk density. Our synthesis across different ecosystems suggests that microbial necromass is predominantly preserved in MAOM, which is driven by climatic factors.