Much recent work has focused on the dynamic nature of the abiotic environment, and on the ways plants respond to these changing conditions. In particular, emphasis has been placed on the importance of variation in light availability for two fundamental aspects of plant performance: growth and defense. However, our understanding of light effects on photosynthesis and synthesis of defensive secondary metabolites comes primarily from temperate high light environments and agricultural systems. In humid tropical forests, light availability at the forest floor is extremely low (<1% full sunlight), with periods of higher light lasting from seconds to hours, depending on the size of the opening in the canopy above. Tree saplings and understory plants must therefore be capable of persisting at extremely low light levels, yet be able to take advantage of short periods of intense and perhaps damaging light. Little is known about how these shade-tolerant species adjust to long-and short-term variation in light availability, despite the fact the majority of the world's species exists under these conditions. The investigators will collect comparative data on photosynthetic physiology, secondary metabolites, and leaf anatomy for a range of shade-tolerant tropical woody species. This will enable them to assess the physiological mechanisms underlying adjustments to long-and short-term variation in light availability, and to track how resources are differentially allocated to growth vs defense.
