Optimal resource allocation in tree canopy under heterogeneous
light environments
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In this study, we aimed to reveal optimal resource allocation patterns in the process of tree canopy formation in heterogeneous light environments by model simulations and pot experiments. Most of woody plants from saplings to mature trees have heterogeneous light environments within their canopy caused by self-shading and/or mutual shading. Consequently, there are branches both in high-light and low-light environments within the canopy. In such a heterogeneous light environments, allocation patterns of nitrogen and water absorbed by root and those of storage carbohydrate and nitrogen used for formation of new leaves to each branch have remained unknown. As a phenomenon that high-light shoots inhibit new shoot formation on low-light shoots of the same tree was reported as “correlative growth inhibition”, it is important to consider resource allocation patterns in heterogeneous light environments to understand a process of canopy formation. In the present study, I first investigated criteria for determining biomass allocation pattern in homogeneous high and low-light environments by optimal biomass allocation model. Then I extended the model to predict growth of a plant in heterogeneous light environments. The model plant has one high-light branch and one low-light branch, and effects of various resource allocation patterns on whole-plant growth rate were analyzed by the dynamic system model. The dynamic system model predicted that whole-plant growth rate is enhanced if storage carbohydrate and nitrogen are allocated more to high-light branch and less to low-light branch in the spring. It was also predicted that concentrating allocation of root-absorbed nitrogen and water to high-light branch don’t enhance whole-plant growth rate in vegetative growth stage. These predictions were tested by pot experiments using saplings of mulberry and maple, and concentrating allocation of storage material to high-light branch was actually observed in the spring. I conclude that tree canopy is formed efficiently by adopting such a resource allocation strategy. |
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