Growth and Senescence of the Successive Grass Leaves on a Tiller. Ontogenic Development and Effect of Temperature

The tiller characteristics (length and age of laminae, number of leaves per tiller) which depend on morphogenetic characters such as leaf appearance and expansion rates, leaf growth duration and leaf lifespan were studied in the field over four growing seasons to gain a better understanding of the progressive changes in leaf digestibility over time, and to facilitate the development of predictive mathematical models. We show that, for a given regrowth, only the number of leaves per tiller and the lamina expansion rate remain constant throughout growth. In other words, the length of successive laminae, their growth duration and lifespan increased while their rate of appearance decreased in such a way that the lamina expansion rate at the tiller level remained constant. These changes were associated with an increase in sheath length which governs both the lamina appearance rate and its growth duration. As temperature increased, the average lamina expansion rate and the number of laminae which grew both increased simultaneously. Therefore, high temperature accelerates the changes in tiller characteristics which occur as growth progresses.