Abstract: The relationship between biodiversity and biogeochemical processes gained much interest in light of the rapidly decreasing biodiversity worldwide. In this article, we discuss the current status, challenges and prospects of functional concepts to plant litter diversity and microbial decomposer diversity. We also evaluate whether these concepts permit a better understanding of how biodiversity is linked to litter decomposition as a key ecosystem process influencing carbon and nutrient cycles. Based on a literature survey, we show that plant litter and microbial diversity matters for decomposition, but that considering numbers of taxonomic units appears overall as little relevant and less useful than functional diversity. However, despite easily available functional litter traits and the well-established theoretical framework for functional litter diversity, the impact of functional litter diversity on decomposition is not yet well enough explored. Defining functional diversity of microorganisms remains one of the biggest challenges for functional approaches to microbial diversity. Recent developments in microarray and metagenomics technology offer promising possibilities in the assessment of the functional structure of microbial communities. This might allow significant progress in measuring functional microbial diversity and ultimately in our ability to predict consequences of biodiversity loss in the decomposer system for biogeochemical processes. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.