Research on mycorrhizas: trends in the past 40 years as expressed in the 'MYCOLIT' database.

A detailed analysis of MYCOLIT, a comprehensive bibliographic database of mycorrhizal research containing almost 12000 references, showed some interesting trends over the past 40 yr. During the last four decades, the average number of papers published per year were 84, 110, 214 and 488, respectively. The current rate of publication is about 700 papers per year. Much research has focused on nutrient dynamics, inoculum production, mycorrhiza formation, and morphology and physiology of both vesicular-arbuscular mycorrhizas (VAM) and ectomycorrhizas (EM). There has been a shift of attention from EM to VAM since 1970. Very little work has been done on the other kinds of mycorrhizas. Barriers to progress in some areas, such as our inability to grow the Glomales in axenic culture, have stimulated a large number of methodological papers over the past decade, while the genetics and molecular biology, especially of VAM, have been neglected. Ecological studies were more numerous than any other kind. However, there was a bias towards laboratory studies as opposed to field studies. Within field studies, researchers focused on agricultural ecosystems, while neglecting disturbed and especially natural systems. This analysis also suggests that we may know less than we think about mycorrhizas, since we have consistently based broad hypotheses and conclusions on studies of a small number of tax. Future research should be directed towards correcting the various imbalances revealed by this analysis.