© 2000 Heron Publishing—Victoria, Canada
Shoot growth responses to light microenvironment and correlative inhibition in tree seedlings under a forest canopy
Akio Takenaka (1)
1. National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-0053, Japan (takenaka@nies.go.jp) / Received October 26, 1999
Summary
To examine the mechanisms underlying crown development, I investigated the dependence of shoot behavior on light microenvironment
in saplings of the evergreen broad-leaved tree species, Litsea acuminata (Bl.) Kurata, growing on a forest floor. The local light environment of individual shoots (shoot irradiance) and plants (plant
irradiance, defined as the shoot irradiance of the most sunlit shoot of a plant) were analyzed as factors affecting shoot
behavior. Daughter shoots that developed under partially sunlit conditions were longer and less leafy than daughter shoots
developed under shaded conditions. Shoot production increased with increasing shoot irradiance. Terminal shoots receiving
5% or less of full sunlight produced 0.67 daughter shoots on average, whereas shoots receiving 10% or more of full sunlight
produced 1.72 daughter shoots. In terminal shoots receiving 5% or less of full sunlight, the probability of producing no daughter
shoots was about 63% when other shoots on the plant received 10% or more of full sunlight, but was < 35% where the rest of
the plant was also shaded. Shoot death was observed only in shoots receiving 5% or less of full sunlight. The mortality of
shaded shoots was higher in plants growing in high irradiance than in plants growing in low irradiance. The ecological significance
of correlative inhibition (the enhanced mortality and reduced production of new shaded shoots in the presence of partially-sunlit
shoots) is discussed.
Keywords:
branching, Litsea acuminata, shoot demography, shoot structure.
