Plant Community Diversity Influences Allocation to Direct Chemical Defence in Plantago lanceolata

Sybille B Unsicker,Anne Mraja,Andrew Hector,Michael Reichelt,Christiane Roscher,Jonathan Gershenzon

doi:10.1371/journal.pone.0028055

Abstract

BackgroundForecasting 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.Methodology/Principal FindingsWe 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/SignificanceOur 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.

Highlights

In the last decades, the important role of plant diversity for ecosystem functioning has been verified in numerous studies [1,2]
Diversity effects on foliar iridoid glycoside concentrations Total foliar iridoid glycoside (IG) concentrations did not vary in response to increasing species richness (Fig. 1a), a significant interaction ‘‘Life stage6SR’’ (Table 1) indicated that species-richness effects on total iridoid glycosides (IG) concentrations depended on life stage
Total IG concentrations decreased with increasing numbers of plant functional groups present in the experimental communities

Summary

Introduction

The important role of plant diversity for ecosystem functioning has been verified in numerous studies [1,2]. Apart from simple increases in plant species richness, other changes in community composition and the presence or absence of certain plant functional groups, legumes and grasses, strongly impact plant performance Changes in plant diversity drastically affect both the biotic and abiotic environment of individual plant species. Herbivore loads and levels of invertebrate herbivory have been shown to be influenced either positively or negatively by increasing plant diversity [16,17]. The multiple changes in the individual plants environment that occur along a diversity gradient require a coordinated response to achieve the appropriate balance among different functions. Experimental data of how plant species diversity influences the investment of individual plants in direct chemical defences against herbivores and pathogens is lacking

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