Production of organic matter and interference of two grasses at different levels of water supply

Arrhenatherum elatius (L.) Presl. (Oatgrass) and Bromus erectus Huds. (Bromegrass) were grown in pots in pure culture and with (a) root, (b) shoot and (c) root and shoot (total) competition with three levels of irrigation. There was one preliminary harvest of shoots and one final harvest of shoots and roots. Plant height, tiller number, and fresh and dry weight were recorded. The plant material was analyzed for protein and acid soluble nitrogen, for total ash, total lipids, carbon, DNA and RNA.

The experiment took place in an unusually dry summer. For this reason both grasses showed nearly the same competitive ability. There was a slight advantage to Arrhenatherum under root and total competition, especially with watering, and a slight advantage for Bromus under shoot competition, with respect to competitive coefficients based on dry matter production. The most distinct effect was the reduction of the root system of Bromus under total competition with watering. The data clearly indicate that water is one of the factors for which Arrhenatherum and Bromus compete.

Although there were only small changes in dry matter production, there were clear differences in the chemical composition of the plants. In the main part of the experiment, Arrhenatherum was able to increase its protein content under root and total competition, whereas Bromus showed a similar tendency only under shoot competition. These data confirm the earlier hypothesis that higher protein content of the green parts causes higher growth rate and thus indicates the stronger competitor. Both grasses exhibited an increase of carbon content under competition, whereas DNA and RNA, inversely related to each other, reacted specifically to root and shoot as well as total competition. These findings cannot be explained without further investigation.