How Soil-Borne Pathogens May Affect Plant Competition

Abstract

A role for pathogens in plant competition has often been suggested, but examples are rare and, in the case of soil pathogens, virtually absent. In this paper we examine if and how soil‐borne pathogens may play a role in plant competition. As a model, two successional plant species from coastal sand dunes were used: Ammophila arenaria (marram grass) and Festuca rubra ssp. arenaria (sand fescue). The root zone of A. arenaria contains pathogens that contribute to the degeneration of their host when dunes become stabilized. These pathogens (plant parasitic nematodes and pathogenic fungi) are relatively harmless to the immediate successor F. rubra. We tested the hypothesis that F. rubra, when grown in a mixed culture with A. arenaria, will be favored when A. arenaria is exposed to soil‐borne pathogens from its own root zone. In a greenhouse, seedlings of both species were grown in replacement series in sterilized (pathogen‐free) and unsterilized (pathogen‐containing) soils originating from the root zone of natural A. arenaria. Nutrient additions, soil moisture, and the length of the experiment were based on two pilot studies. When exposed to its soil‐borne pathogens, A. arenaria was outcompeted, especially when it constituted <50% of the planted mixture. Nutrient limitation enhanced the replacement of A. arenaria by F. rubra especially in unsterilized soil. This was due to reduced plasticity of A. arenaria in responding to nutrient limitation when exposed to its pathogens. The present results support previous suggestions that soil pathogen‐driven competition may be an important mechanism in species replacement in coastal foredune vegetation.

Density-dependency and plant-soil feedback: former plant abundance influences competitive interactions between two grassland plant species through plant-soil feedbacks

“…We hypothesized that negative plant-soil feedbacks would be stronger in the 1:1 plant mixture than in plant monocultures (Kardol et al 2007; Petermann et al 2008; van der Putten and Peters 1997). We found only limited evidence for this.…”

Plant–soil feedback of native and range-expanding plant species is insensitive to temperature

“…We did not include changes in water availability, length of growing season, frequency of extreme events and direct effects of increased CO 2 . These can all affect plant–soil interaction (van der Putten and Peters 1997; Chakraborty and Datta 2003; Ainsworth and Long 2005; Suttle et al 2007; Kreyling et al 2008) and these effects may co-vary with increased temperatures. Therefore, these factors need to be investigated in future studies for a more complete understanding of the effects of climate change.…”

Interactions between nematodes and their microbial enemies in coastal sand dunes

“…This phenomenon also occurs for Ammophila breviligulata in North America, and has been studied in parallel. Soil-borne pathogens and parasites, particularly plant-parasitic nematodes (PPN), are considered to be involved in both the die-back and successional decline of marram grass (Van der Putten et al 1988, 1993Van der Putten and Peters 1997). This has been demonstrated by glasshouse experiments where the application of fungicides and nematicides to marram grass seedlings growing in non-sterile soil promoted plant growth, suggesting the involvement of soil fungi and PPN in a disease complex of marram grass (de Rooij-van der Goes 1995; Van der Putten 1990).…”