Weirauch, S. K. | Search bioRxiv

bioRxiv2026

Drought and Herbivory Shape Growth and Chemical Traits in Black Poplar (Populus nigra)

Due to climate change, extreme weather events such as droughts are becoming more frequent and intense. This has a profound impact on plant performance and ecological interactions, including those involving herbivorous insects. The combined impact of drought stress and insect herbivory on plant metabolism has rarely been studied, particularly in woody plants. In this study, we investigated the influence of varying degrees of drought, both alone and in combination with herbivory by the leaf beetle Chrysomela tremulae, on the morphological and chemical characteristics of black poplar (Populus nigra) trees using a full factorial experimental design. We quantified morphological traits, volatile organic compound (VOC) emissions, phytohormone and amino acid concentrations, and phenolic profiles. Drought conditions increased the concentrations of salicylic acid (SA) and abscisic acid (ABA), while feeding induced ABA and SA. Amino acid profiles shifted significantly under drought conditions, particularly in beetle-infested plants. In contrast, salicinoids, which are the most important phenolic defense compounds in poplars, remained relatively stable. We also observed significant compound-specific effects on both constitutive and herbivore-induced VOC emissions. Our results demonstrate that drought and insect herbivory exert a joint influence on the chemical responses of P. nigra across multiple metabolic pathways. These findings highlight how the interaction between abiotic and biotic stresses can influence the defense chemistry of trees, which will consequently affect ecological interactions in forest ecosystems in the face of climate change.

ecology↗

bioRxiv2026

Common, species-specific, and accession-specific responses of foliar phytohormones and morphological traits to drought and herbivory

BackgroundPlants are exposed to various environmental challenges. With ongoing climate change, droughts and insect outbreaks are expected to become more frequent. Thus, a better understanding is needed of how different plant species respond to such single and combined challenges. This study investigated common versus species-specific responses to environmental challenges in three perennial plant species of different growth forms and whether responses differ intraspecifically among accessions. Clones of different accessions of the herbaceous species Tanacetum vulgare, the woody vine Solanum dulcamara, and the tree Populus nigra were subjected to similar control, herbivory, drought, and combined (drought and herbivory) treatments for the same periods. After the exposure, concentrations of foliar phytohormones and various morphological traits were measured. ResultsAcross all species, several foliar phytohormones and one of ten morphological traits responded consistently to the environmental challenges. Jasmonoyl-isoleucine was induced by herbivory and the combined treatment, abscisic acid (ABA) by drought and the combined treatment, and indole acetic acid by the combined treatment in all species. Root mass remained unchanged in all species. However, structural equation models (SEMs) revealed a shared regulatory pathway across species in which ABA connected treatment and root mass, indicating a common hormonal response potentially linking challenges to growth responses. Despite these common patterns, species-specific responses were pronounced. In P. nigra, a unique induction of salicylic acid was found under the combined treatment, while aboveground mass and root-shoot ratio remained unaffected by any treatment, in contrast to the other two species. Species-specific SEMs further indicated distinct phytohormone-mediated pathways underlying morphological variation. Phenotypic plasticity reflected these species-specific patterns, with none of the phytohormones or morphological traits exhibiting uniform plasticity across species. Intraspecific variation further shaped responses, as phytohormone and morphological trait plasticity depended on accession, indicating substantial accession-specific plant responses. ConclusionsOur results indicate that some responses to comparable challenges may be conserved across species, while others are species-specific. The combined treatment elicited the most pronounced responses, and such complex responses may become more frequent under current global change. Our study highlights that comprehensive understanding of plant responses requires systematic comparisons at both interspecific and intraspecific scales.

ecology↗