MYCORRHIZAL DYNAMICS OF 3 WOODLAND HERBS OF CONTRASTING PHENOLOGY ALONG TOPOGRAPHIC GRADIENTS

Vesicular-arbuscular mycorrhizal (VAM) dynamics of three woodland herb s of differing phenology were examined along contiguous topographic gr adients in two southwestern Ohio forests during 1992-1994. Cardamine c oncatenata (Brassicaceae) exhibited VAM colonization only during senes cence in May, whereas Trillium flexipes and Smilacina racemosa exhibit ed 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%, res pectively. Overall, analysis of variance (ANOVA) indicated significant seasonal effects with summer months having higher mean PRLC, and wint er and early spring months having the lowest. ANOVA also indicated a s ignificant effect due to topography, with uplands and slopes having gr eater mean PRLC than lowlands. The significantly lower mean PRLC for b oth T. flexipes and S. racemosa may have reflected higher phosphate av ailability in the spring, cooler temperatures, and/or moister conditio ns. The significantly lower mean PRLC in lowland positions may be due to greater soil moisture throughout the year. These results support th e hypothesis that VAM development is lower in moister topographic posi tions, however, they do not support the hypothesis that VAM developmen t would increase with decreasing P availability. Consequently, moistur e appeared more important than P in regulating VAM development in thes e sites.