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The effect of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolikum perenne L. cv. parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at tow levels of nitrogen (N) supply (no additional N and 200 kg N ha-1) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations in open- top chamebers. Stands were cut foru times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measued. In addition, plant height of both species at harves dats and during several regrowth periods was monitored. Results indicate that both species made demand on different resources and profited from growht in a mixed sward. CO2- related yield increase amounted to 16-42% for white clover whera the effect of high CO2 on rygrass yield ranged between -33% and +9% dependign on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was singifcantly enhanced by CO2 enrichment at many harvests in both N supply treaements. Without additional N supply, shoot competition for lighr was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petriles grew longer and ryegrass was shorter at elevated CO2. With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. [ABSTRACT FROM AUTHOR]

Pure stands of Trifolium repens L. N.Z. Huia and Lolium perenne L. S32 and mixtures of various densities and frequencies were treated with sulphuric acid solutions of pH 2.5, 3.5 and 5.6. The species yield was recorded over live sequential harvests. Multifactorial response equations were used to describe the behavior of the species yield as a function of acidity and the density of both species. Predictions, made through these models, showed that the response of yield of these species to simulated acid rain treatments varied greatly depending on the planting density, the time of harvesting and on whether the plants were growing in monoculture or in mixture. This suggests that it is not sufficient to consider the effects of experimentally applied acid rain on single individuals or low density stands, since the results obtained will not reflect the response in a close canopy sward. [ABSTRACT FROM AUTHOR]

Shoot concentrations of Se associated with a 10% reduction in dry matter yield were established for perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) grown in sand culture. Selenite-treated plants had lower shoot concentrations of Se than those treated with selenate; the critical toxic values associated with a 10% reduction in growth were 48 and 320 µg Se g-1 dry matter shoots for ryegrass plants, and 160 and 330 µ Se g-1 dry matter shoots for white clover plants, respectively. Differences in the mode of absorption of selenite and selenate, and in the distribution and chemical form of Sc found in the plant after absorption, probably account for this disparity in toxicity. While both selenate and selenite increased the Se concentration in the tissues of the plants to high levels, a greater proportion of the absorbed Se was transported to the shoots of the selenate-treated plants than of those treated with selenite. Increasing supplies of selenate were associated with a reduction in chlorophyll content. Contrary to the concept of a common uptake mechanism in the roots for selenate and sulphate, increasing supplies of selenate had a synergistic effect on S concentrations in the shoots rather than the expected antagonistic effect. [ABSTRACT FROM AUTHOR]

In six experiments Lolium perenne L. and Plantago lanceolata L. were grown together in pots. Two experiments also included L. perenne alone, P. lanceolata alone, or L. perenne + Trifolium repens L. In five of the experiments prior sterilization of the soil followed by reinoculation was used to obtain two treatments, one having plants infected with vesicular-arbuscular mycorrhiza, the other non-mycorrhizal. The shoots of some plants in each pot ('donors') were injected with 32P. After a week these shoots were removed, and after a further week the remaining plants ('receivers') were harvested and their 32P content determined. In all experiments and species-combinations there was some 32P transfer to the shoots of both mycorrhizal and non-mycorrhizal receiver plants. The amount of transfer in mycorrhizal treatments was 2 to 8-fold greater than in non-mycorrhizal treatments, except in one experiment where mycorrhizal infection was very low. There was no clear difference between the different species combinations in the amount by which phosphorus transfer was enhanced by mycorrhizas. These results show that mycorrhizas can increase phosphorus transport between plants, but do not show whether there is direct transport from one root to another via interconnecting hyphae or whether the phosphorus must leave the donor root before being taken up by mycorrhizal hyphae. [ABSTRACT FROM AUTHOR]