Date of Award:

5-1-1976

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

Ivan G. Palmblad

Committee

Ivan G. Palmblad

Committee

Arthur Holmgren

Committee

James MacMahon

Committee

George Welkie

Committee

M. Coburn. Williams

Abstract

A model of adaptive germination was tested by observing germination responses of six annual weed species with respect to soil nitrate levels. Setaria lutescens (Weigel) Hubbard, Echinochloa crusgalli (L.) Beauv., and Amaranthus retroflexus L. were selected as species for which it would be adaptive to increase germination percentages when soil nitrate was high. Avena fatua L., Brassica nigra (L.) Koch, and Medicago lupulina L. were selected as species for which it woμld be adaptive to decrease germination percentages when soil nitrate was high. A controlled environment was used for the experiments, except for one field experiment with M. lupulina. Emphasis was on simulating the conditions encountered by populations in the field. No evidence for adaptive germination with respect to nitrate level could be found for the six species tested. Concomitant experiments with A. retroflexus, E. crusgalli, and S. lutescens used ammonium for the treatments, but again produced no effects of nitrogen level on germination percentage. The nitrogen levels ranged from 1 to 225 ppm in soil solution at field capacity. When conditions were relaxed by using A. retroflexus and S. lutescens seeds in freshly harvested condition, the latter species showed some increase in germination with higher nitrate levels. Logistic equations were fitted by regression to the cumulative germination curves of S. lutescens and A. retroflexus, with the coefficient of determination ranging from 80 to 95 percent. The rate parameter of the equations exhibited no relationship to the nitrogen level. Both rate and total appear to be sensitive to environment prior to germination and to population sampling error, but rate is the variable more sensitive to environment during germination. Seed catalase activity declines when A. retroflexus and S. lutescens are subjected to cold, moist conditions in soil. These results contradict those reported in the literature. Although this decline is consistent with the loss of nitrate stimulated germination in S. lutescens during overwintering, most freshly harvested seeds do not have their dormancy imposed by high catalase levels alone. Possible reasons for the noncongruence of the results with the predictions of the model are discussed.

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