Vegetation forms a key interface between Earth surface and atmosphere. The important role of vegetation carbon, water and energy exchanges is well established, but the overall impact of plant trace gas (VOC) emission for large-scale Earth processes is poorly understood. Although it is widely accepted that VOCs play major roles in the formation of ozone, secondary organic aerosols (SOA) and cloud condensation nuclei (CNN) with potentially profound impacts on air quality and Earth radiative balance, the research has so far focused only on constitutive emissions from species considered “emitters”. However, differently from constitutive VOCs emitted only by certain species, all plant species can be triggered to emit induced VOCs under abiotic and biotic stress. So far, induced high-reactivity VOCs are not considered in global VOC budget, and thus, this proposal tests the key assumption that VOC emissions worldwide have been vastly underestimated. As global change is resulting in higher level of stress in Earth ecosystems, the relevance of induced emissions is further expected to gain in importance. The current project has the overall objective to evaluate the effect of plant-generated VOC emissions on air composition and environment under global change, with particular emphasis on the role of VOCs induced in response to environmental stress. The study first quantifies the VOC production vs. stress severity relationships across species with differing stress tolerance and advances and parameterizes the qualitative induced VOC model developed by PI. The novel quantitative model is further verified by flux measurements and scaled up to regional and global scales to assess the contribution of induced emissions to overall VOC budget, and study the feedbacks between stress, ozone, SOA and CNN formation and the Earth climate using an hierarchy of available models. This highly cross-disciplinary project is expected to result in key contributions in two research fields of major significance: plant stress tolerance from molecules to globe and the role of vegetation component in atmospheric reactivity and Earth climate. The first part of the study provides fundamental insight into the stress responsiveness of plants with differing tolerance to environmental limitations, extending “leaf economics spectrum”, a hotspot of current plant ecology research. The second part provides quantitative information on large-scale importance of plant VOCs in globally changing climates with major relevance for understanding the role of plants in the Earth’s large scale processes.