Abstract
The relationships between photosynthesis rate of leaves and specific leaf area (SLA) were elucidated in 50 plants from five timothy varieties. There were significantly. negative correlationships between photosynthesis rate and SLA through the growing season and the correlationship was closest (r=-0.763)in June, the heading time of timothy plants. The varietal differences existed in both the photosynthesis rate and SLA, for instance, CLIMAX was a variety showing high photosynthesis rate and low SLA, and S 51 was a variety showing low photosynthesis rate and high SLA. The timothy plants with high photosynthesis rates during the heading season had a considerably high possibility of showing high photosynthesis rates during another season. As the correlationship between photosynthesis rate and SLA became closest in the heading time (June), it was considered most effective to use SLA observed in this time as a criterion for the selection of timothy plants with high photosynthesis rates. Using 32 plants from four timothy varieties, the influences of day length on photosynthesis rate of leaves and SLA were investigated. During the mild air temperature (16℃) season (August-September) the timothy leaves grown under the long day (18 hours day length) condition showed higher photosynthesis rates than those grown under the natural day length (14 hours) condition. Contrary to this, during the cool (9.6℃) season (October-November) the photosynthesis rates were lower in the leaves grown under the long day condition. The influences of interaction of day length and air temperature on the photosynthesis rate were recognized. The values of SLA had a tendency of increasing under the long day condition at both the mild and low air temperature.
