Acidity impacts on microbial diversity and litter decomposition for organic soils

•Background: Dissolved organic carbon (DOC) concentrations have increased in soil solutions and surface waters over the past 30 years in acid sensitive areas of Europe and Northern America. This has been linked to recovery from acidification of soils with decreasing levels of atmospheric pollution. Whilst previous research has found pH related DOC solubility is a likely driver of increased DOC concentrations in surface waters, it is unclear whether increased DOC production from organic matter decomposition, due to more favourable pH conditions for biological activity, has also contributed to the rising trends in surface waters. •Aim: We investigated how acidity impacts microbial communities, the decomposition of litter types common to acid-sensitive ecosystems, and the impact on DOC production. •Methods: A decomposition study using litter bags and the Tea Bag Index was incorporated into an established acidity manipulation field experiment across two sites with contrasting acid deposition histories, and two characteristic soil types (peats and peaty podzols). •Results: We found higher rates of litter decomposition in podzol soil than peat leading to higher DOC production and aromaticity, as indicated by absorbance properties. Acidity manipulations did not influence decomposition rates for most litter types, DOC production for any litter type, Tea Bag Index parameters (stabilisation factor and decomposition rate) or microbial diversity, for any site or soil type. •Conclusion: Our study suggests that decomposition of aboveground-collected litter does not mediate acidity effects on DOC production, whilst soil type, and physiochemical soil responses to acidity, are more influential on DOC release from organic soils.