Plant biodiversity is changing in terrestrial ecosystems at unprecedented rates as human activities alter the global climate and fragment landscapes. Plants provide important ecosystem functions: they create habitats for organisms, sequester carbon from the atmosphere, and drive soil nutrient cycling. Many ecological studies have established clear relationships between biodiversity and ecosystem functioning. Yet, we still do not fully understand how plant diversity affects ecosystem processes on different spatial and temporal scales.
The central goal of this project is to understand how tree diversity contributes to forest ecosystem function across time. Our research in the second Forest and Biodiversity (FAB2) experiment at the Cedar Creek Ecosystem Science Reserve (CCESR) tests how tree community composition influences photosynthetic functioning, light stress, and health of trees. We hypothesize that greater phylogenetic and functional diversity of trees leads to increased productivity and less light-induced stress of trees in forest ecosystems due to optimized niche partitioning and facilitation between neighbor trees throughout the growing season. We test this hypothesis by using in-situ methods to accurately predict aboveground plant chemical traits through time at the individual plant and community levels.
Understanding how abiotic and biotic factors affect photosynthetic mechanisms can give us insight into how tree community composition affects ecosystem functioning. Chlorophyll fluorescence measurements were made to understand how neighbor trees affected each other’s light stress levels at multiple timepoints in the 2021 growing season. Results show that non-photochemical quenching of leaves (NPQ), a measure of stress induced by excess light, generally decreased with increasing shade at the plot level, expressed in leaf area index (LAI). In addition to reduced light-induced stress, electron transport rates (ETR) increased in tree communities with more LAI. Elevated ETR are indicative of higher rates of photosynthesis. Multiple linear regressions were run to examine the relationships. The adj. R2 for NPQ is 0.3158 and the adj. R2 for ETR is 0.3818. One potential reason for this observed trend is that neighboring trees of taller heights and greater LAI can offer shade to light-sensitive trees. Thus, functionally diverse tree communities may contribute to higher productivity when some trees benefit from the shade provided by others. This benefit may be more pronounced in the early part of the growing season when leaves are developing and are more sensitive to excess light.