Abstract
Biodiversity and ecosystem functioning research typically shows positive diversity- productivity relationships. However, local increases in species richness can increase competition within trophic levels, reducing the efficacy of intertrophic level population control. Pseudomonas spp. are a dominant group of soil bacteria that play key roles in plant growth promotion and control of crop fungal pathogens. Here we show that Pseudomonas spp. richness is positively correlated with take-all disease in wheat and with yield losses of ~3 t/ha in the field. We modeled the interactions between Pseudomonas and the take-all pathogen in abstract experimental microcosms, and show that increased bacterial genotypic richness escalates bacterial antagonism and decreases the ability of the bacterial community to inhibit growth of the take-all pathogen. Future work is required to determine the generality of these negative biodiversity effects on different media and directly at infection zones on root surfaces. However, the increase in competition between bacteria at high genotypic richness and the potential loss of fungal biocontrol activity highlights an important mechanism to explain the negative Pseudomonas diversity-wheat yield relationship we observed in the field. Together our results suggest that the effect of biodiversity on ecosystem functioning can depend on both the function and trophic level of interest.
Highlights
IntroductionThe putative role of some Pseudomonas spp. in take-all control, and their general dominance in the soil bacterial community, positions them as a useful focal group taxon to explore the phenomenon of take-all build up, and to test more general ideas of how bacterial diversity in wheat root system might be related to fungal pathogen suppression
We tested if the ratio of log(Φobs/Φexp) differed between levels of richness and phylogenetic diversity.We found that increasing Pseudomonas genotypic richness was associated with a reduced inhibition of the fungal pathogen, beyond that expected from the additive inhibitory effects of individual Pseudomonas genotypes (F1, 37 = 10.45, P = 0.003; Fig. 4a)
Our field trials show that take-all disease severity, and crop grain losses are positively associated with increased Pseudomonas genotypic richness in wheat rhizospheres
Summary
The putative role of some Pseudomonas spp. in take-all control, and their general dominance in the soil bacterial community, positions them as a useful focal group taxon to explore the phenomenon of take-all build up, and to test more general ideas of how bacterial diversity in wheat root system might be related to fungal pathogen suppression. We used field trials to test if the genotypic richness Pseudomonas spp. in wheat root systems is correlated to severity of infection by the take-all pathogen and yield loss (e.g. Fig. 1). We tested for generic changes in the background rhizosphere bacterial community structure based on relative abundance of 16S rRNA genes and sub-sampled culturable isolates in both the endosphere and rhizosphere of wheat roots to describe the patterns of Pseudomonas spp. genotypic richness and phylogenetic diversity across pre-culture treatments at finer resolution. We conducted a complementary set of competition experiments to test if the effects of Pseudomonas genotypic richness on inhibition of the take-all pathogen could be explained by the degree of antagonism between bacteria expressed in Pseudomonas mixtures (defined here as the compound effects of direct antagonistic toxin production and indirect exploitative resource competition)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
