REVIEW AND SYNTHESIS

Studies of trace gases in the atmosphere, their sources, sinks, and me chanisms of transport, have developed rapidly in the last few decades. This has been driven partly by increasing recognition that particular gases are associated with problems such as acidification, eutrophicat ion, and global warming, but also by the developing enthusiasm for mul tidisciplinary research in which scientists from many disciplines coll aborate to explore biological, geochemical, and atmospheric cycles and to understand how human action disturbs such cycles. Major internatio nal programs such as the International Biological Program (IBP) and th e International Geosphere-Biosphere Program (IGBP) have been very infl uential in generating and encouraging this new way of working. To answ er these complex environmental research questions, scientists have nee ded to develop new field instrumentation, or at least to modify instru ments normally used in the laboratory. Equally, mathematical simulatio n models are increasingly being used at scales ranging from cellular t o global to allow complex computations that would have been unthinkabl e even a decade ago. The papers in this proceedings illustrate some of the exciting developments taking place in the study of the exchange o f trace gases between the atmosphere and the land. They describe new u nderstanding of the processes in soils, plants and the atmosphere that control gases important in the carbon and nitrogen cycles, they summa rize new techniques and instrumentation that allow field studies at sc ales ranging from soil grains to landscapes, and they present results of mathematical models that allow us to explore consequences of global changes that may yet come.