Responses of Plants from Three Successional Communities to a Nutrient Gradient

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Abstract
Seventeen plant species [Abutilon theoprasti, Amaranthus retroflexus, Ambrosia artemisiifolia, Chenopodium album, Polygonum pensylvanicum, Setaria faberii, Aster pilosus, Sorghastrum nutans, Daucus carota, Oenothera biennis, Solidago canadensis, Vernonia altissima, Andropogon gerardii, Aster laevis, Petalostemum purpureum, Ratibidia pinnata and Solidago rigida] from communities of early, mid- and late successional position were examined for their response to a gradient of nutrients. All species germinated over a wide range of nutrient concentrations. The early successional species began and completed germination sooner at all nutrient concentrations than did late successional species. There was an increase in total germination at moderate nutrient concentrations, but at the highest concentration, germination of most of the species was reduced. Plant survival at higher nutrient concentrations was significantly less than at low concentrations. The early successional species were less affected than were mid- and late successional species. Most of the species from the early and late successional assemblages grew fastest at the intermediate nutrient concentration, while the mid-successional species grew fastest at the low nutrient concentration. Early successional species had higher concentrations of nutrients in their shoots and more marked changes in shoot nutrient concentration with increased concentration of nutrients in the soil than did species from mid- and late successional assemblages. Species from the late successional community had narrower response breadths and smaller proportional similarity among them than did species of the earlier assemblages. From the observed differences in niche breadth and similarity at the different successional positions, past competition resulting in niche divergence was probably most important in the organization of the late successional community, while competition within each season was important in the organization of the early successional community but only after other factors had determined the number and identity of the competitors.

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