Doetterl, S. | Search bioRxiv

bioRxiv2026

Floral scent diversity and evolution in deceptive Cypripedium, and post-pollination effects on floral scent and its biosynthesis in C. henryi

Background and Aims: Floral scent is a primary driver of pollinator attraction and reproductive isolation in deceptive orchids. Yet, little is known about the variation and evolution of scent in a phylogenetic framework and how pollination affects the biosynthesis and emission of scents in these lineages. This study characterizes scent diversity across Cypripedium, a genus of deceptive orchids, examines phylogenetic constraints, and investigates post-pollination effects on scent composition in one of the species. Methods: Floral volatile organic compounds (VOCs) were sampled from 31 Cypripedium taxa using dynamic headspace techniques, and analysed by gas chromatography coupled to mass spectrometry (GC/MS). Uni- and multivariate methods were used to analyse intra- and interspecific scent variation and test for phylogenetic signal in floral scent. Post-pollination effects on scent composition were experimentally tested in C. henryi using four pollination treatments, combined with RNA-seq analyses of floral tissues to examine transcriptional responses in VOC biosynthetic pathways. Key results: We detected 258 floral VOCs, revealing a high chemical diversity dominated by terpenoids, aliphatics, and aromatic compounds. Floral scent composition was highly species-specific, and closely related taxa often shared only few compounds. Scent composition differed among pollination groups, but these groups explained only a limited proportion of overall scent variation. We detected a significant but weak phylogenetic signal, suggesting limited evolutionary constraint in floral scent. Pollination had limited effect on C. henryis floral scent and volatile biosynthesis gene expression, despite a significant decrease in total scent emission after pollinium deposition. Transcriptional changes predominantly occurred in the petals rather than the labellum and staminode. Conclusion: Floral scent evolution in Cypripedium is characterized by high chemical diversity, and a weak phylogenetic constraint, consistent with variable selection in food-deceptive systems. The pollination study further suggests the absence of a strong, directed post-pollination effect on the floral scent of C. henryi. Keywords: Cypripedium; deceptive pollination; floral scent; volatile organic compounds (VOCs); phylogenetic signal; linalool; post-pollination effects; transcriptome profiles; differential gene expression; floral organs

plant biology↗

bioRxiv2026

Microbial carbon metabolism is linked to organic matter chemistry across soil systems

Soil microbial growth and respiration play a critical role for soil organic carbon dynamics. Yet, we lack understanding of the main controls of soil microbial carbon metabolism at large scales. Here, we investigated whether and how the chemical composition of microbially available organic matter affects soil microbial carbon metabolism across soil systems. We linked soil microbial growth and respiration rates as well as carbon use efficiency (quantified with 18O stable isotope probing) to the chemical composition of extractable organic matter (characterized with reversed-phase liquid chromatography coupled to Fourier-transform ion cyclotron resonance mass spectrometry) along a geoclimatic gradient of 33 Chilean temperate grassland soils. We found that biomass-normalized rates of growth and respiration were primarily positively linked to aliphatics such as carbohydrate-, proteinaceous- and amino sugar-like compounds, and secondarily to unsaturated lignin-like compounds. Respiration was positively linked to compounds with carbon in a reduced oxidation state, suggesting carbon-conserving catabolism, while growth appeared unrelated to the oxidation state of carbon. This suggests that other mechanisms than mere energetic constraints control microbial growth rates in aerated soils. Our findings demonstrate that information on the chemical composition of bioavailable organic matter can provide insights into the processes that govern the fate of carbon across different ecosystems. Key pointsO_LIWe investigated if bulk soil microbial growth (18O stable isotope probing) and respiration is linked to the chemical composition of extractable organic matter (LC-FT-ICR MS) along a geoclimatic gradient of temperate grasslands. C_LIO_LIHigher rates of microbial carbon turnover were positively linked to aliphatic and unsaturated compounds. C_LIO_LISpecific (i.e., biomass-normalized) respiration was positively linked to compounds with carbon in a reduced oxidation state, suggesting carbon-conserving catabolism. C_LIO_LISpecific growth was unrelated to the oxidation states of substrate carbon, suggesting that soil microbial substrate use for anabolism may not be determined by direct energetic constraints. C_LI

microbiology↗