Production of the first one to three leaves requires a substantial amount of energy in the form of carbohydrates stored in the crown of the plant. However, as these first leaves fully extend, rapid rates of photosynthesis supply sufficient carbohydrates for growth of other leaves and roots. When severe defoliation occurs, carbohydrates stored in the roots and crowns may be needed to initiate new growth. Leaves have a definite life span, as do tillers. The first spring leaf normally dies in the summer.
Leaves are most photosynthetically active when they reach full expansion.
As they age, their capacity for photosynthesis declines. The excess carbohydrate produced through photosynthesis helps produce additional leaves, reproductive organs or roots. Thus, photosynthate produced by the plant is used efficiently in growth and maintenance. Once a leaf can no longer produce enough carbohydrates through photosynthesis for its own needs, it dies. Reproductive Growth Grasses often begin a transition from vegetative to reproductive growth when most of the vegetative growth is produced for that year.