How functional traits influence plant growth and shade tolerance across the life cycle

Abstract

<p id="d1847087e195">Plant species differ in many functional traits—features of specific tissues and allocation of energy among them. While traits have been used in many correlative approaches to describe communities and demography, it has remained unclear how and why traits should influence whole-plant growth. Here, we present a theoretical framework for understanding the effect of traits on plant growth and shade tolerance. This framework captures diverse patterns of growth in relation to size and explains why the effect of traits on growth changes through ontogeny. By disentangling the effects of plant size, light environment, and traits on growth rates, this study provides a theoretical foundation for understanding growth across diverse tree species around the world. </p><p class="first" id="d1847087e198">Plant species differ in many functional traits that drive differences in rates of photosynthesis, biomass allocation, and tissue turnover. However, it remains unclear how—and even if—such traits influence whole-plant growth, with the simple linear relationships predicted by existing theory often lacking empirical support. Here, we present a theoretical framework for understanding the effect of diverse functional traits on plant growth and shade tolerance by extending a widely used model, linking growth rate in seedlings with a single leaf trait, to explicitly include influences of size, light environment, and five prominent traits: seed mass, height at maturation, leaf mass per unit leaf area, leaf nitrogen per unit leaf area, and wood density. Based on biomass growth and allocation, this framework explains why the influence of traits on growth rate and shade tolerance often varies with plant size and why the impact of size on growth varies among traits. Specifically, we demonstrate why for height growth the influence of: ( <i>i</i>) leaf mass per unit leaf area is strong in small plants but weakens with size; ( <i>ii</i>) leaf nitrogen per unit leaf area does not change with size; ( <i>iii</i>) wood density is present across sizes; ( <i>iv</i>) height at maturation strengthens with size; and ( <i>v</i>) seed mass decreases with size. Moreover, we show how traits moderate plant responses to light environment and also determine shade tolerance, supporting diverse empirical results. </p>