Kitajima’s research interests

As a plant functional ecologist, I am interested in the ecological and evolutionary significance of various morphological, physiological and developmental traits of plants. I seek a deeper understanding of the adaptive significance of functional traits, i.e., traits that influence ecological performance, such as growth and survival, in interaction with biotic and abiotic environmental factors. My general approach is to describe and compare phenotypic variations of functional traits both in natural habitats and under experimental conditions in which ontogenetic stages and environmental conditions are standardized. This approach allows me to evaluate how functional traits are determined by the interplay of genetic differences, developmental patterns and environmental factors. I am particularly interested in trait syndromes associated with carbon-allocation strategies, life-history trade-offs and niche specialization in species-rich tropical forests. Because light is the most critical resource for juvenile survival and competitive interactions among trees in moist and wet tropical forests, species differences in shade tolerance are considered to be central for forest community dynamics and assembly.

The most important goal of my research program is to improve functional understanding of the trait diversity among tropical trees and its influence on ecological dynamics in species-rich tropical forests. The dominant paradigm on shade tolerance used to postulate that efficient utilization of limited light was the basis of shade tolerance. This perspective, however, has been repeatedly rejected by the results of my projects that examined how photosynthetic light-utilization and carbon allocation patterns affect growth and survival. Instead, my studies have consistently demonstrated that shade tolerance requires maintenance of positive net carbon balance over a long-term through 1) defensive traits to cope with various biotic and abiotic hazards and 2) energy-reserves that allow a quick recovery from tissue loss when these hazards could not be prevented, even though such allocation strategy means inefficient light use and slower growth rates. My comparative studies of leaf traits also have demonstrated a parallel between leaf traits and whole-plant traits, such that well-defended leaves inefficient in light utilization are selected when plants become adapted to shade. In other words, shade-adapted species have lower productivity and grow more slowly in shade in order to achieve high survival compared species adapted to more open environment. This “counter-intuitive idea” has become increasingly accepted during the last 15 years as studies by others find independent support for it.

The majority of my research projects on community-wide comparison of plant functional traits have been conducted in Neotropical forests in Panama and Bolivia. Most of my work in Florida, in contrast, has aimed to elucidate the functional basis for the competitiveness of several exotic invasive plant species.  In addition, I am increasingly interested in application of plant functional ecology to evaluate the impacts of global changes on ecosystem carbon balance and community dynamics in coupled human-natural systems in the tropical forest biome. In all these research areas, my work has shown that ecological significance of physiological and morphological traits of plants require consideration of their ecological interactions with not only abiotic environmental factors such as light and soil nutrients and other plants, but also biotic factors, i.e., animals and microbes that may act as consumers, pathogens, or mutualists.

Ecophysiology of upper forest canopy of tropical forests, in particular carbon balance in response to environmental factors and climate change

© Kaoru Kitajima 2016