The persistence of mineral-associated organic matter varies with time and litter quality

Soil organic matter is often divided into particulate organic matter (POM), which is assumed to turn over fast, and mineral-associated organic matter (MAOM), which is assumed to persist in soil for extended periods. However, recent studies indicate quick turnover of part of MAOM. While it is well established that litter quality and soil history affect POM and MAOM formation, little is known about how these factors govern the decomposability of POM and MAOM. To address this gap, we investigated the turnover of MAOM relative to that of POM in soils of various ages supplied with litter of varying quality. We used POM and MAOM extracted from soil at different times after major disturbance across three different chronosequences in the Czech Republic. These chronosequences included abandoned fields and sites in which soil developed de novo , either by spontaneous processes or under plantations of N-fixing alder trees. The decomposability of POM and MAOM was evaluated via heterotrophic microbial respiration from these fractions in a 6-week incubation. Overall, cumulative respiration per gram C did not differ between POM and MAOM at the end of the incubation. However, respiration from both POM and MAOM decreased over the course of the incubation. During the first 3 days of incubation, significantly more CO 2 was respired from POM than from MAOM. In the individual chronosequences, more CO 2 was respired from MAOM than from POM under N-fixing alder trees. Our results indicate that the decomposition of MAOM can be faster than that of POM, which is more likely after supply with easily decomposable litter. These findings support recent evidence that part of MAOM cycles rapidly and show that its decomposability depends on ecosystem development and litter quality, emphasizing the context dependency of MAOM persistence.