Germination of Co-Occurring Annual Species on a Soil Moisture Gradient

Abstract

To determine possible mechanisms of habitat differentiation, germination of stratified seeds of 6 colonizing species which occur together in 1st-yr oldfields, was tested on a soil moisture gradient. Seeds of Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, Chenopodium album, Polygonum pensylvanicum and Setaria faberii were sown on a controlled soil moisture gradient ranging from flooded conditions down to 4.7% moisture content per soil dry weight. Much of the gradient was unsuitable for germination of any species. The species showed no differentiation in response along the gradient. Proportional similarity was high. .beta.-Niche breadths were also high, but not as high as those of established plants of these species, which exploit a wider range of the gradient. Although there is no differential response of germination to soil moisture, other aspects of germination behavior may contribute to coexistence.