Biodiversity changes atmospheric chemistry through plant volatiles and particles

Given the significant human-induced changes in biodiversity and climate, the link between atmospheric and biological measurements is crucial to improve our understanding of atmosphere-biosphere feedbacks. Changes in climate and biodiversity influence the emission of biogenic volatile organic compounds (BVOCs) from plants, leading to the formation of biogenic secondary organic aerosols (BSOA). These BSOA can have diverse effects, including influencing Earth's radiative balance and impacting cloud and precipitation formation. However, at present, it is unclear how changing biodiversity will lead to changes in BVOC emissions, BSOA and their corresponding effects. We present a conceptual framework of the relationships between biodiversity and BVOC emissions based on our current mechanistic understanding and combining knowledge from the fields of biology and atmospheric chemistry. In this framework, first, we hypothesized that mixed forests enable resource partitioning, often leading to higher stand productivity and leaf area index, thus emitting higher amounts of BVOC. Second, given the significant difference in biotic and abiotic stress in monoculture and mixture plots, we hypothesized that increasing tree diversity would decrease BVOC emissions. We tested the effect of tree diversity on BVOC emission and BSOA formation in this framework by varying tree species richness, including monocultures, two- and four-species mixtures at the MyDiv experimental site in Germany. We quantified nine different BVOCs from the investigated plots, i.e., α-pinene, camphene, β-pinene, 3-carene, p-cymene, limonene, α-terpinene, isophorone, and acetophenone. The relative differences in tree monocultures and mixtures show that the overall concentration of BVOC decreases with increasing biodiversity. For BSOA, a total of fifteen BSOA compounds have been quantified, including diaterpenylic acid acetate [DTAA], 3-methyl-1,2,3-butanetricarboxylic acid [MBTCA], norpinonic acid, pinonic acid, terebic acid, terpenylic acid, pinic acid, adipic acid, pimelic acid, azelaic acid, suberic acid, succinic acid, glutaric acid, salicylic acid, and sebacic acid. The relative differences in tree monocultures and mixtures for BSOA showed mixed and overall non-significant results. A deeper understanding of how changing biodiversity influences biogenic organic compound emissions and biogenic secondary organic aerosol formation requires in-depth investigations of microclimate conditions, accurate monitoring of above- and below-ground biotic and abiotic stress, and manipulating stress conditions across long-term biodiversity experiments. Our findings highlight the need for multidisciplinary work at the interface between the biosphere and the atmosphere to better understand the reciprocal effects of biodiversity and climate change.