FEEDBACK BETWEEN PLANTS AND THEIR SOIL COMMUNITIES IN AN OLD FIELD COMMUNITY

The nature of the interaction between plants and their soil community was investigated by testing for differential responses of four old-field perennial plant species to inocula derived from soil communities that had been grown with (''cultured by'') one of these four plant species. The differentiation of the soil communities was evident in measurements of plant survival, phenology, growth, and root-shoot ratios. Effects on survival and growth suggest negative feedbacks between these species and the soil communities that they culture. Survival rates of Krigia dandelion were significantly reduced when grown with their ''own'' soil community. Considered as a whole, the three other species (all grasses) had significantly lower growth and root-shoot ratios when grown with soil communities started with their own inocula compared to soil communities started with the inocula of other species. However, the significance of this effect on growth rate and root-shoot ratios was due primarily to the pairwise comparison of Anthoxanthum odoratum and Danthonia spicata and of Anthoxanthum and Panicum sphaerocarpon, respectively. Pairwise comparisons of Danthonia and Panicum do not suggest differential responses to each other's soils in growth rate or root-shoot ratios nor do soil communities appear to affect the relative competitive ability of these two species. While the components of the soil community responsible for these effects have not been identified, similar although less pronounced patterns were observed in experiments using inocula consisting of washed live root segments as compared to experiments using whole soil as inoculum, suggesting that root pathogens are one important agent.