Drying and rewetting effects on organic matter mineralisation of contrasting soils after 36 years of storage

Abstract Soil incubation studies commonly use archived, dry stored soil samples. Numerous studies have detected a profound impact of dry storage on soil microbial community composition and activity. However, comparatively few studies have explored the impact of storage on the short-term mineralisation of soil organic matter (SOM) after moistening dry soils to revive and stabilise microbial activity (“pre-incubation”). We examined whether pre-incubation of dry stored soil of contrasting texture (Alfisol and Vertisol) can recover native soil microbial functions in fresh soil or soil stored for 3 weeks, 3 or 36 years. The oldest samples had a delayed CO 2 response after moistening, but matched CO 2 production rates of younger samples within hours. The two soil types displayed contrasting CO 2 emission responses after moistening; the Alfisols had a rapid but short-lived CO 2 emission peak (the so-called “Birch Effect”) while the Vertisols demonstrated a long, sustained release of CO 2 reflecting its higher abundance of microsite abundance and microaggregates which may protect SOM and microorganisms during adverse conditions like drying. After 10 days of pre-incubation, older Alfisol samples had higher protease activity and response to amino acid addition demonstrating altered microbial physiological responses relating to nitrogen (N) compared to fresher counterparts. However, such responses in Vertisols were unchanged suggesting high clay soils with high potential microsite abundance may improve preservation of soil N functions through dry storage or even drought. This work highlights both limitations and possibilities of incubating dry archived soils for SOM mineralisation studies.