THE EFFECT OF HANDLING ON PHOTOSYNTHESIS, TRANSPIRATION, RESPIRATION,AND NITROGEN AND CARBOHYDRATE CONTENT OF POPULATIONS OF LOLIUM-PERENNE

Two populations of perennial ryegrass (Lolium perenne L.) S23, selecte d for contrasting rates of yield and mature leaf dark respiration, wer e used in this study. Since previous work showed that yield decreased severely in population GL66 due to mechanical perturbation, possible e ffects on respiration rates were examined. Apart from a transient incr ease in population GL72, there was no effect on the respiration rate, but mechanical perturbation did affect other processes. Handling cause d transpiration rates in the light to increase for GL72, and in the da rk to decrease for GL66. In the longer term, the nitrogen content decr eased in handled plants grown at high density. These results emphasize that handling plants should be reduced to a minimum since it might ha ve major effects on several processes, II is concluded that the origin al selection for the Lolium populations was indeed on contrasting rate s in yield and respiration. Furthermore it is argued that the existenc e of low- and high-yielding genotypes can be attributed to the dissimi lar responses of different genotypes to mechanical influence.