Intra- and interspecific soil feedback as a driver of coexistence and ecosystem function

Background/Question/Methods

The processes that maintain coexistence between species have been a central topic of scientific discussion in Ecology for decades. In addition to resource niches, other mechanisms imparting negative density dependence have received increasing attention. In plant communities, negative soil feedbacks resulting from the accumulation of species-specific soil pathogens have been studied extensively in recent years. These feedbacks have been shown to operate in many plant communities from tropical forests to temperate grasslands. They have the potential to maintain coexistence even in the presence of large fitness differences between plant species. Negative soil feedbacks have also been associated with the higher productivity of diverse plant communities, possibly being one of the major drivers of the positive biodiversity-functioning relationship. However, all of these processes have so far almost exclusively been studied at the species or functional group level.
Here, we used one of the most famous model organisms in biology, Arabidopsis thaliana and other Arabidopsisspecies in greenhouse experiments to study the role of soil feedback in the maintenance of coexistence and ecosystem function within and between species and relate this feedback to morphological trait similarities.

Results/Conclusions

We found that ten different ecotypes of A. thaliana exhibited soil feedbacks that ranged from strongly negative to strongly positive. The plants produced different quantities of biomass and seeds depending on whether they grew on soils previously occupied by their own ecotype or by other ecotypes. The ecotypes differed strongly in their above- and belowground traits. However, the strength and direction of the soil feedback was independent of any of the measured traits. We furthermore found that productivity of communities assembled from ten different ecotypes produced more biomass than single-ecotype assemblages. In a further experiment using A. thaliana and A. lasiocarpa we are testing whether soil feedbacks are stronger at the between-species level than within species and if the strength of the feedback can be linked to trait differences and the differential use of nutrients of these species.
Our results show that soil feedbacks are not only important at the species level but also occur intraspecifically. Thus, they have the potential to contribute to the stabilization of genotypic diversity and to the positive effect of intraspecific diversity on ecosystem function. Using soil feedback experiments at different taxonomic levels is bringing us closer to understanding the fundamentals of coexistence in ecological communities.