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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]

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]