Dissolved organic matter in soils - future directions and unanswered questions

Dissolved organic matter (DOM) is an important constituent of soil solution that plays a role in many chemical and biological processes in soils. Tremendous strides have been made in the past 25 years to more fully describe the composition of DOM and its role in soil. The papers in this special issue contribute to this literature by both summarizing recent research and reporting on new projects. Based on the papers presented here and others in the literature, I suggest that the following three questions would prove fruitful for future research on DOM in soils: (1) How large are various sources and sinks and how are they controlled?; (2) What is the ecological significance of dissolved organic nitrogen (DON) in comparison to dissolved organic carbon (DOC)?; (3) How are fluxes altered in human-dominated environments? In support of answering these questions, I recommend that emphasis be placed on developing new analytical techniques (isotopic, or detailed characterization of DOM constituents), increasing interchanges between aquatic and terrestrial biogeochemists and developing an integrated conceptual approach to the study of DOM in soils that addresses interactions among solid soil organic matter, microorganisms including fungi and mycorrhizal fungi, and DOM. (C) 2002 Elsevier Science B.V. All rights reserved.