Landucci, L. | bioRxiv Science

bioRxiv2026

Comparative nectar metabolomics reveals sucrose-nitrogen tradeoffs and chemical drivers of microbial growth in floral nectar

IntroductionMany plant species secrete nectar to attract beneficial animals. The chemical composition of floral nectar influences pollinator nutrition and behavior, as well as microbial growth in flowers. Yet factors that predict nectar composition across plant species, as well as chemical compounds determining microbial growth in nectar, remain poorly understood. MethodsWe used both targeted and untargeted metabolomics to compare the nectar chemical profiles across 31 phylogenetically diverse plant species that span a range of floral morphologies. We examined the common classes of compounds detected in nectar and patterns of co-occurrence among them. We combined newly collected chemical data with previously published data on microbial growth in nectar of the same plant species to examine how nectar chemistry is associated with microbial growth. ResultsPlant species and clades varied in amino acid, minor sugar, and secondary metabolite composition and concentration. Sampled rosids and lilioids generally contained higher amino acids while asterids contained greater concentrations of oligosaccharides and sugar alcohols. Across plant species, proteinogenic amino acids frequently co-occurred in nectar but many were negatively associated with sucrose concentration. Plant species with greater concentrations of amino acids and other nitrogen-containing compounds hosted greater microbial density in nectar, while some other compound groups were negatively associated with microbial diversity. ConclusionsNegative correlations between nectar amino acid and sucrose concentration across species suggest ecological tradeoffs or physiological constraints in nectar composition. Given that the growth of common nectar microbes is limited by amino acid concentration, these findings suggest an ecological cost to amino acid production in nectar. Finally, we document variation among species in nectar vitamins, non proteinogenic amino acids and secondary metabolites with hypothesized yet currently untested ecological roles.

plant biology↗

bioRxiv2024

Plant species vary in nectar peroxide, an antimicrobial defense tolerated by some bacteria and yeasts

Floral nectar attracts pollinators but can also harbor microbes including plant pathogens. Nectar contains antimicrobial constituents including hydrogen peroxide, yet it is unclear how widespread nectar hydrogen peroxide might be among plant species or how effective against common nectar microbes. Here, we surveyed 45 flowering plant species distributed across 23 families and reviewed the literature for measurements of 13 other species to assess the field-realistic range of nectar hydrogen peroxide (Aim 1) and explored whether plant defense hormones induce nectar hydrogen peroxide upregulation (Aim 2). Further, we tested the hypotheses that variation in microbial tolerance to peroxide is predicted by microbe isolation environment (Aim 3), that increasing hydrogen peroxide in flowers alters microbial abundance and community assembly (Aim 4), and that microbial community context affects microbial tolerance to peroxide (Aim 5). We found that sampled plants contained nectar hydrogen peroxide ranging from 0 to 2940 {micro}M, although half of the sampled species concentrations were less than 100 {micro}M. While plant defensive hormones did not change the concentration of hydrogen peroxide in floral nectar, enzymatically upregulated concentrations in living flowers significantly reduced microbial growth. Together, our results suggest that nectar peroxide is a common but not pervasive antimicrobial defense among nectar-producing plants. In addition, nectar microbes vary in tolerance and detoxification ability, and co-growth can facilitate the survival and growth of less tolerant species, suggesting a key role for community dynamics in microbial colonization of nectar.

plant biology↗