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Organized Oral Session

Session: : Integrating Light Spectra to Understand the Causes and Consequences of Variation in Plant Function Across Biological Scales

OOS 51-2 - Cross-scale consequences of light quality in diverse tree communities.

Thursday, August 10, 2023
8:15 AM – 8:30 AM PDT
Location: 254
In closed-canopy forests, photosynthetically active light is a resource that can limit the carbon assimilation and growth of individual trees. Partitioning light via differences among trees in physiology, phenology or architecture is a key way in which mixed species forests may be more productive than monospecific ones. However, light may shape forest function not only as a resource but also as a cue. Plants can perceive light at various wavelengths in the UV-B, blue, green, red, and far red. They can use this information to assess their neighborhoods and adjust their allocation toward growth and defence. Such light-mediated shifts in plant function could, in theory, shape relationships between diversity and productivity. While these cues and their physiological consequences have been well established in laboratory studies, how they play out across diversity gradients and in ecosystems with rich and complex signals—like forests—is unknown. Here we explored relationships between tree diversity, light quality, and plant function. Across four tree diversity experiments in two continents, amounting to >250 tree plots planted with one to 12 species, we characterized light quality, canopy structure, leaf optical properties, and leaf secondary chemistry among and within tree canopies. At the top, middle and bottom of the canopy on each plot, we measured irradiance at all wavelengths known to elicit biological activity, from the ultraviolet to shortwave infrared, and measured leaf area index to indicate canopy structure. We sampled leaves from the top, middle and bottom of the crowns of each species on each plot, and we measured their reflectance and transmittance and secondary chemistry. Our results show how tree diversity relates to light quality, illustrate how canopy structure and leaf optical properties both shape and are shaped by these relationships, and demonstrate how light quality mediates biological consequences across scales of organization from the production of secondary metabolites in leaves to forest function. Ultimately, our study lends deeper and mechanistic insight into light-related drivers of the relationship between biodiversity and the functioning of forest ecosystems.