| Zusammenfassung: | Vesicular-arbuscular mycorrhizal (VAM) dynamics of three woodland herbs of differing phenology were examined along contiguous topographic gradients in two southwestern Ohio forests during 1992-1994. Cardamine concatenata (Brassicaceae) exhibited VAM colonization only during senescence in May, whereas Trillium flexipes and Smilacina racemosa exhibited robust VAM development throughout the year. The lowest mean percent root length colonized (PRLC) for T. flexipes and S. racemosa was 38.3% and 37.7%, respectively, while the greatest was 80.2% and 80.8%, respectively. Overall, analysis of variance (ANOVA) indicated significant seasonal effects with summer months having higher mean PRLC, and winter and early spring months having the lowest. ANOVA also indicated a significant effect due to topography, with uplands and slopes having greater mean PRLC than lowlands. The significantly lower mean PRLC for both T. flexipes and S. racemosa may have reflected higher phosphate availability in the spring, cooler temperatures, and/or moister conditions. The significantly lower mean PRLC in lowland positions may be due to greater soil moisture throughout the year. These results support the hypothesis that VAM development is lower in moister topographic positions, however, they do not support the hypothesis that VAM development would increase with decreasing P availability. Consequently, moisture appeared more important than P in regulating VAM development in these sites.
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