Physiological responses to light explain competition and facilitation in a tree diversity experiment

Ecologists often invoke interspecific facilitation to help explain positive biodiversity–ecosystem function relationships in plant communities, but seldom test how it occurs. One mechanism through which one species may facilitate another is by ameliorating abiotic stress. Physiological experiments show that a chronic excess of light can cause stress depresses carbon assimilation. If shading plant's neighbours reduces enough, growth. instead most limiting factor for photosynthesis, have an adverse, competitive effect. In temperate tree diversity experiment, we measured stem growth rates and photosynthetic physiology broadleaf trees across gradient availability imposed their neighbours. At the extremes, experienced nearly full sun (monoculture), or were shaded nearby fast-growing conifers (shaded biculture). Most had slower with larger neighbours, implying net On other hand, two shade-tolerant (Tilia americana Acer negundo) shade-intolerant (Betula papyrifera) faster The greatest increases photoinhibition (reduced dark-acclimated Fv/Fm) increasing availability, suggests they are more vulnerable While lower assimilation biculture treatment, T. up 25% higher. also dropped its leaves 3–4 weeks earlier monocultures, curtailing growing season. We conclude although large limitation species, increase amelioration species. Finally, B. papyrifera, find pattern elongation shade avoidance response account apparent trend volume. Synthesis. Both negative interactions our experiment be explained part responses environment created underlie relationships. insights ecologists gain searching such physiological mechanisms us forecast under environmental change.