Deciphering the Biotic and Climatic Factors That Influence Floral Scents: A Systematic Review of Floral Volatile Emissions

Abstract

Currently, a global analysis of the information available on the relative composition of the floral scents of a very diverse variety of plant species is missing. Such analysis may reveal general patterns on the distribution and dominance of the volatile compounds that form these mixtures, and may also allow measuring the effects of factors such as the phylogeny, pollination vectors, and climatic conditions on the floral scents of the species. To fill this gap, we compiled published data on the relative compositions and emission rates of volatile organic compounds (VOCs) in the floral scents of 305 plant species from 66 families. We also gathered information on the groups of pollinators that visited the flowers and the climatic conditions in the areas of distribution of these species. This information allowed us to characterize the occurrence and relative abundances of individual volatiles in floral scents and the effects of biotic and climatic factors on floral scent. The monoterpenes trans-bocimene and linalool and the benzenoid benzaldehyde were the most abundant floral VOCs, in both ubiquity and predominance in the floral blends. Floral VOC richness and relative composition were moderately preserved traits across the phylogeny. The reliance on different pollinator groups and the climate also had important effects on floral VOC richness, composition, and emission rates of the species. Our results support the hypothesis that key compounds or compounds originating from specific biosynthetic pathways mediate the attraction of the main pollinators. Our results also indicate a prevalence of monoterpenes in the floral blends of plants that grow in drier conditions, which could link with the fact that monoterpene emissions protect plants against oxidative stresses throughout drought periods and their emissions are enhanced under moderate drought stress. Sesquiterpenes, in turn, were positively correlated with mean annual temperature, supporting that sesquiterpene emissions are dominated mainly by ambient temperature. This study is the first to quantitatively summarise data on floral-scent emissions and provides new insights into the biotic and climatic factors that influence floral scents.

Flower Production, Headspace Volatiles, Pollen Nutrients, and Florivory in Tanacetum vulgare Chemotypes

“…The higher pollen compound diversity later in the blooming season may provide a better defense of the pollen against robbery ( Celedon and Bohlmann, 2019 ). Under natural conditions, in addition also changes in temperatures and in the occurrence of drought events later in the season may affect the composition and chemodiversity of flower volatiles ( Farré-Armengol et al, 2020 ). We expected plant individuals with a high floral headspace chemodiversity to produce less pollen, potentially due to higher enzymatic costs.…”

“…Indeed, the extent to which the composition and concentrations of primary metabolites such as amino acids and sugars within reward traits and specialized metabolites (i.e., compounds that are often restricted to certain plant taxa, formally known as secondary metabolites) such as headspace volatile compounds ( Knudsen et al, 2006 ) and pigments within floral tissues ( Harborne and Smith, 1972 ) differ across plant species is remarkable ( Borghi et al, 2017 ). For example, more than 1700 volatile chemicals have been identified from floral headspace samples of different plant species ( Knudsen et al, 2006 ), with terpenoids and benzenoids occurring most frequently ( Knudsen et al, 2006 ; Farré-Armengol et al, 2015 , 2020 ). The species-specific floral scent bouquet is in the majority of cases an attractant, but not always an honest signal for the presence of reward traits such as nectar and/or pollen ( Knauer and Schiestl, 2015 ) and enables flower visitors to identify their host flowers.…”

Shared semiochemicals in a tri-trophic system benefit crop plants

“…For example, benzaldehyde is commonly dispensed in orchards to attract plum curculio (Conotrachelus nenuphar) to traps (Piñero et al 2001, Prokopy et al 2003. Benzaldehyde is also released by plants and is one of the most widely distributed oral VOCs (Farré-Armengol et al 2020), with a known attractiveness to pollinators (Huber et al 2005, Theis 2006). Further, new active semiochemical release devices being used such as aerosol 'puffers' are capable of releasing signi cantly larger volumes of compounds when compared to more traditional passive open dispersion devices.…”

Plant Volatile Organic Compounds Evolution: Transcriptional Regulation, Epigenetics and Polyploidy

“…Therefore, epigenetic change would propose a flexible evolutionary mechanism and help to explain the continuous gain and loss of specific VOCs in related plant lineages. Epigenetic variations would assist plants in surfing on an adaptative landscape in which abiotic and biotic interactions usually involve trade-offs (e.g., herbivory and pollinator attraction) [ 137 , 138 ].…”