title: Plant community diversity influences allocation to direct chemical defence in Plantago lanceolata.
abstract: BACKGROUND
  Forecasting the consequences of accelerating rates of changes in biodiversity for ecosystem functioning requires a mechanistic understanding of the relationships between the structure of biological communities and variation in plant functional characteristics. So far, experimental data of how plant species diversity influences the investment of individual plants in direct chemical defences against herbivores and pathogens is lacking.
  
  
  RESULTS
  We used Plantago lanceolata as a model species in experimental grasslands differing in species richness and composition (Jena Experiment) to investigate foliar concentrations of the iridoid glycosides (IG), catalpol and its biosynthetic precursor aucubin. Total IG and aucubin concentrations decreased, while catalpol concentrations increased with increasing plant diversity in terms of species or functional group richness. Negative plant diversity effects on total IG and aucubin concentrations correlated with increasing specific leaf area of P. lanceolata, suggesting that greater allocation to light acquisition reduced the investment into these carbon-based defence components. In contrast, increasing leaf nitrogen concentrations best explained increasing concentrations of the biosynthetically more advanced IG, catalpol. Observed levels of leaf damage explained a significant proportion of variation in total IG and aucubin concentrations, but did not account for variance in catalpol concentrations.
  
  
  CONCLUSIONS
  Our results clearly show that plants growing in communities of varying species richness and composition differ in their defensive chemistry, which may modulate plant susceptibility to enemy attack and consequently their interactions with higher trophic level organisms.
authors.affiliation: Max Planck Institute for Chemical Ecology, Jena, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Mraja
authors.forename: Sybille B
authors.initials: SB
authors.lastname: Unsicker
authors.forename: Michael
authors.initials: M
authors.lastname: Reichelt
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gershenzon
authors.forename: Christiane
authors.initials: C
authors.lastname: Roscher
mesh_terms: D044822:Biodiversity; D057888:Iridoid Glucosides / Q000378:metabolism*; D008027:Light; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D010943:Plantago / Q000276:immunology* / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects; D013045:Species Specificity
chemical_list: D057888:Iridoid Glucosides; C078040:catalpol; C006650:aucubin; D009584:Nitrogen