Vegetative Responses of Bromus inermis to Certain Variations in Environment

Abstract

1. Vegetative responses of diverse plants of smooth brome grass (Bromus inermis Leyss.) to variations in soil temperature, container size, clipping intensity, and shading were investigated in the greenhouses and garden of the University of Chicago with plants derived from both clonal divisions and seed from diverse places of origin. The responses of the individual plants were measured in one or more of the following ways: stem count; total oven-dry top weight; root count; and total oven-dry root weight. 2. The effects of clipping upon plants of diverse origins were studied in three separate experiments: clipping in greenhouse (seventeen clones); clipping in garden (twenty-two clones); and clipping seedlings in greenhouse (three strains of diverse origin). Three series were run in the experiments on clones started in April, 1946: series C, control; series 1, clipped once; and series 2, clipped twice in the 1946 growing season. Throughout the course of the experiments with clonal materials, which were terminated in June; 1947, stem counts were made and dry weights of clipped tops determined. Dry weights of tops and roots were determined for the seedlings. At the final harvest dry weights of tops and roots and the number of stems were inversely proportional to frequency of clipping. In the greenhouse experiment, where light and temperature as well as container size were limiting factors, the weight per stem did not seem to be affected by clipping, but in the garden experiment it was inversely correlated with frequency of clipping. It was further found that clipping was more adverse in its effects upon root growth than upon top growth and that the effect upon both carried over into the season following clipping. 3. Divisions of four clones were grown at soil temperatures of 20⚬, 26⚬ and 31⚬ C. Greatest total top weight was produced at 20⚬ C. in three clones of northern origin and at 26⚬ in one clone of southern origin. At all temperatures the increase in number of stems was less in the clipped series than in the unclipped, and the increase was inversely proportional to the soil temperature. One northern clone did not survive clipping at 31⚬ C., and another died at both the 31⚬ and the 26⚬ soil temperatures. The weight of single roots and the total root weight in each clone showed a much stronger inverse correlation with soil temperature than did total top weight. 4. Three divisions of twenty, three different clones were brought into the green-house from the garden and planted in 8-inch clay pots in late April, 1946. one series was placed on a well-lighted bench in the greenhouse, another under a single layer of sheeting, and the third was placed under a double layer of sheeting. Relative light intensities were: outside, 100; greenhouse, 46; one layer of cloth, 14; two layers, 5. At the lowest intensity only four clones survived until the fall of 946. In the spring of 1947, when the experiment was terminated, ten clones were still alive under the single layer of sheeting, seventeen were still alive in the control series, but none had survived in the most shaded series 5. Divisions of four clones were grown in unglazed clay pots of five different sizes, in 8-inch glazed pots, and in 12inch-square wooden boxes. With the exception of the plants in the glazed pots, the final stem count, oven-dry top yield, top yield per original stem, total root number, top-weight/ root-weight ratio, top yield per root, and ratio of weight per stem/weight per root were directly proportional to the size of the container. In the glazed pots the plants were as vigorous as in clay pots two and a half times larger.