Plant–soil feedbacks contribute to an intransitive competitive network that promotes both genetic and species diversity

Abstract

Summary1. Plant communities are generally thought to follow strict competitive hierarchies, in which species can be linearly ordered according to their ability to compete for a few limiting resources. Such strict hierarchies should lead to reduced diversity, since the single best competitor will eventually exclude the other species. However, more complex dynamics may emerge if different plant species or genotypes compete in different ways, such as through the release of toxic allelochemicals or the alteration of soil microbial communities. 2. Brassica nigra genotypes and their competitor species show a 'rock-paper-scissors' like dynamic, in which no one type is competitively superior to all others. This intransitive dynamic can maintain both species diversity and genetic variation in an allelochemical trait of B. nigra. 3. Here we show that feedbacks with soil biota, probably involving arbuscular mycorrhizal fungi, facilitate these dynamics. Brassica nigra genotypes that invest heavily in the allelochemical sinigrin reduce mycorrhizal abundance of surrounding soils, which reduces the growth of heterospecific competitors. Since B. nigra is non-mycorrhizal, investment in sinigrin does not improve a genotype's ability to compete with other conspecifics. 4. Synthesis. These results highlight the importance of complex soil communities for the maintenance of both genetic and species diversity in plant communities.

The relative importance of rapid evolution for plant-microbe interactions depends on ecological context

“…First, plant genotypes are known to influence microbial communities [18,19]. Second, plantsoil feedbacks can contribute to plant-plant competitive interactions and coexistence [41][42][43], and recent studies suggest that plant-soil feedbacks can contribute to fitness differences among plant genotypes within a species [18,44]. Finally, eco-evo dynamics are expected to occur when organisms have large effects on their environment and as a result can alter the selective environment for themselves and other species in the community (i.e.…”

Microbes as Targets and Mediators of Allelopathy in Plants

“…While declines in AMF infection rates of native species would seemingly have negative fitness effects, it is not always clear that changes in AMF community composition, when seen, will necessarily have negative effects on competing plants (but see Lankau, 2011a). Providing additional support for potentially important allelopathic effects are reports of the impact of other weedy Brassicaceous species on mycorrhizae, including that of Brassica nigra (Lankau et al, 2011) and Sysimbrium loeselii (Bainard et al, 2009), but none of these cases have been as fully developed as that of Alliaria, and may be subject to the same limitations that intensive study of this species has revealed. The role of glucosinolates in effects of Brassicaceous species on mycorrhizae also remains to be fully elucidated.…”

Intraspecific genetic variation and species coexistence in plant communities

“…The reason for the negative impact of sinigrin on heterospecific plants can, at least partly, be explained by the toxic effects of sinigrin on mycorrhizal fungi in the soil. Most heterospecifics benefit from mycorrhiza association, whereas Brassica is non-mycorrhizal and hence not affected by reduced mycorrhizae in the soil [31]. High concentration genotypes are favoured when B. nigra is rare and most often competes against heterospecifics but are disfavoured as B. nigra becomes more abundant and increasingly competes against conspecifics.…”