Irradiance and Developmental Stages of Crown Architecture Affect Shoot Production in &amp;lt;i&amp;gt;Rhododendron reticulatum&amp;lt;/i&amp;gt;

Kenichi Yoshimura

doi:10.4236/ajps.2013.45a011

Abstract

Plasticity in crown architecture, contributing to leaf arrangement within crown, is an important feature for whole plant carbon assimilation and survival. In this study, I examined the plasticity in crown architecture to light condition and developmental stage by the changes in shoot production. Rhododendron reticulatum expands crown with orthotropic growth in monopodial branching in young stage, but orthotropic growth is ceased in adult stage. Main stem of young crown is described with monopodial branching regardless of light environment. But multi-layer crown is observed in sun-lit environment rather than mono-layer crown in adult stage. Long shoot production for each branching system (foliage derived from sympodial branching) in young crown is associated with local light environment, but not in adult crown. Long shoot production rate is correlated with long shoot production rate of its mother shoot in young crown, but not in mono-layer crown. These results suggest that young crown expands branches to sun-lit position whereas adult crown reduces congestion of shoots with stochastic shoot production regardless of shoot production of mother shoots. I concluded that both light and developmental stage are important factors for shoot production and constructing crown architecture.

Highlights

Plants growing in the forest understory, where insufficient irradiance limits the assimilation rates, have minimally overlapping branches and leaves for efficient sunlight reception and better carbon benefit against carbon investment
Decrease of long shoot production rate from the previous year long shoots over the years in young and multi-layer crowns indicates shoot production becomes lower along years in sympodial branching
Short shoots, which are often found in the internal crown, are supposed to cause a decrease in long shoot production for avoiding self-shading

Summary

Introduction

Plants growing in the forest understory, where insufficient irradiance limits the assimilation rates, have minimally overlapping branches and leaves for efficient sunlight reception and better carbon benefit against carbon investment. Shrub species, growing in the forest understory throughout their lifecycle, especially have higher morphological plasticity in crown architecture to survive the shaded condition [1,2]. Crown architecture is represented as a species-specific growth strategy in response to variable light environments. Pioneer species, which grow rapidly under high light intensity, show multi-layer crown architectures to receive sun light including direct beam and sunlight transmitted through upper leaf layers [3]. Late-successional species, which grow under low light intensity, show mono-layer crown architectures that can receive at least limited sunlight and avoid self-shading because sunlight transmitted through upper leaf layers does not satisfy the sufficient assimilation [3,4]. Saplings of Abies mariesii growing in open conditions show multi-layer crown architectures and those growing in shaded conditions show monolayer crown architectures [5]

Methods

Results

Conclusion