TIME CHANGES OF RELATIVE GROWTH-RATE IN 2 NATURAL POPULATIONS OF DACTYLIS-GLOMERATA L

Changes in the relative growth-rate (RGR) between successive harvests were studied in two natural populations of Dactylis glomerata, one from Norway and the other from Portugal, grown at four temperatures in a 16-h photoperiod. Young seedlings were harvested at six equal intervals of 7 days at 5 and 10 °C and 3.5 days at 20 and 30 °C. Quadratic curves were fitted to loge dry weight by a method employing inverse matrices. There was a decline in RGR with time and the magnitude of this decline differed for the two populations with an intersection of the curves at each temperature. At 5 and 10 °C the RGR of the Portuguese population was greater than that of the Norwegian at the initial harvests, but it declined more rapidly than the RGR of the Norwegian population. This relationship was reversed at 20 and 30 °C, with the RGR of the Norwegian population being greater when the plants were small, and declining more rapidly with time. The implications of these changes in RGR are discussed in relation to earlier growth-analysis experiments where only two harvests were taken. © 1969 OXFORD UNIVERSITY PRESS.