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Knius, E., Kolloffel, C. and Lamhers, H. 1994. The effecl of handling on photosynthesis, transpiration, respiration, and nitrogen and cai bohydrate conteni of populations of Uiiiuin perenne. -Physiol Plam. 91: "(i31-63W.Two popui'ations of perennial ryegrass i Loiium perenne L.) S23. selected fo]-contrasting rales of yield and maiure ieaf dark lespiralion. were used in this study. Since previous work showed ihat yield decreased seveiely in population GL66 due to mechanical periurbalion. possible effects on respiialion i-ates were e.xamined. .^pari irotii a ti'ansient increase in population GL72, there was no effec! on the respiration rate, but i-nechanical pei'ttirbation did affect other processes. Handling caused transpiration raies in the light to increase for GL72, and in Ihe dark lo decrease for GL66. In the longer term, the niliogen content decreased in handled plants gro\\n al high density.These resulls emphasize thai handling phints should be iedueed to a minimum since it might have major effects on several processes. It is concluded thai the origii-ial selection for the Loiiimi pcipulations was indeed on conirastiiig rales in >ield and respiration. Furthermore it is argued thai the existence of low-and higli-ytelding genotypes can be attributed to the dissimiljr responses of diflerenl genotypes to mechanical influence

Autotoxicity and allelopathy affect the respiration and yield of GL66 and GL72, two populations of perennial ryegrass (Lolium perenne L. cv. S23) that were originally selected for contrasting rates of mature-leaf dark respiration under conditions where allelopathic effects could not occur and autotoxic effects were minimal. The aim of this study was to further investigate growth and biomass allocation of these two populations in relation to their autotoxic and allelopathic properties. To this end, plants were subjected to two conditions (monoculture and mixed culture) and two treatments (growth in 'renewed' and 'replenished' nutrient solution, allowing for short- and long-term accumulation of allelochemicals, respectively). The fast-respiring population, GL66, showed a reduced total yield due to allelopathic effects only when long-term accumulation of allelochemicals was allowed (mixed culture, replenished). However, short-term accumulation (mixed culture, renewed) of allelochemicals was sufficient to affect allocation of biomass to leaf sheaths. The slow-respiring population, GL72, suffered from autotoxicity only when long-term accumulation was allowed (monoculture, replenished), and from allelopathy under both short- and long-term accumulation (mixed culture, either renewed or replenished). The predominant allelopathic and autotoxic effect was on dry matter percentage and dry weight of leaf sheaths. We conclude that the roots of both populations release one or more chemical compounds that primarily affect biomass allocation to leaf sheaths, both of the same and of the other population. Sensitivity to the putative inhibitor(s) released by the other population was greater than sensitivity to the inhibitor(s) released by a population's own roots.

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