Species-specific effects of polyploidisation and plant traits of Centaurea maculosa and Senecio inaequidens on rhizosphere microorganisms

Abstract

Invasive plant species represent a threat to terrestrial ecosystems, but their effects on the soil biota and the mechanisms involved are not yet well understood. Many invasive species have undergone polyploidisation, leading to the coexistence of various cytotypes in the native range, whereas, in most cases, only one cytotype is present in the introduced range. Since genetic variation within a species can modify soil rhizosphere communities, we studied the effects of different cytotypes and ranges (native diploid, native tetraploid and introduced tetraploid) of Centaurea maculosa and Senecio inaequidens on microbial biomass carbon, rhizosphere total DNA content and bacterial communities of a standard soil in relation to plant functional traits. There was no overall significant difference in microbial biomass between cytotypes. The variation of rhizosphere total DNA content and bacterial community structure according to cytotype was species specific. The rhizosphere DNA content of S. inaequidens decreased with polyploidisation in the native range but did not vary for C. maculosa. In contrast, the bacterial community structure of C. maculosa was affected by polyploidisation and its diversity increased, whereas there was no significant change for S. inaequidens. Traits of S. inaequidens were correlated to the rhizosphere biota. Bacterial diversity and total DNA content were positively correlated with resource allocation to belowground growth and late flowering, whereas microbial biomass carbon was negatively correlated to investment in reproduction. There were no correlations between traits of the cytotypes of C. maculosa and corresponding rhizosphere soil biota. This study shows that polyploidisation may affect rhizosphere bacterial community composition, but that effects vary among plant species. Such changes may contribute to the success of invasive polyploid genotypes in the introduced range.

Eco‐evolutionary dynamics in plant–soil feedbacks

“…However, these effects of genotype are species dependent, as different cytotypes of Centaurea maculosa (spotted knapweed) had no effect on soil microbial communities (Thébault et al . ).…”

“…Similarly, Senecio inaequidens (narrow-leafed ragwort) produces different genotypes, or cytotypes, as a result of polyploidy. Cytotype affects flowering phenology and the ratio of resource allocation to reproduction vs. below-ground growth, which alters bacterial diversity and abundance in the soil (Th ebault et al 2010). However, these effects of genotype are species dependent, as different cytotypes of Centaurea maculosa (spotted knapweed) had no effect on soil microbial communities (Th ebault et al 2010).…”

Species interactions and plant polyploidy

“…Because polyploidy can cause changes in physiology such as secondary chemistry, nutrient use, or photosynthetic rates that could have a direct impact on soil microbes, we might expect polyploidy to induce large changes in the soil community (e.g., Knight et al, 2005; Thébault et al, 2010). In the only study comparing soil communities of diploids and tetraploids, Thébault et al (2010) showed that soil bacterial diversity increased in pots containing tetraploid Centaurea maculosa and that the abundance of nonbacterial microbes decreased in soil containing tetraploid Senecio inaequidens . These results suggest a species‐specific pattern that might be caused by selection following whole‐genome duplication.…”

Complex interactions between spatial pattern of resident species and invasiveness of newly arriving species affect invasibility

“…Native from western Asia to western Europe, Centaurea stoebe was introduced in the PaciWc Northwest of the United States in the late 1800s (Watson and Renney 1974) and expanded rapidly throughout north-western America and western Canada, where it is now widespread in rangelands, pastures, and on roadsides (Skinner et al 2000;Duncan 2001). Introduced genotypes are known to induce changes in soil bacterial communities, which may explain their invasion success (Thébault et al 2010). Seeds of C. stoebe were collected during summer 2005 throughout its native range in Europe as well as in Montana and Oregon, USA, in its introduced range (Broennimann et al 2007;Treier et al 2009).…”

“…These two species: (1) belong to the same family (Asteraceae); (2) occupy similar ecological niches in their native range; and (3) tend to invade similar habitats in their introduced range. However, previous studies have shown that they have two diVerent invasion mechanisms: Senecio inaequidens relies on an increased propagule pressure to invade (Thébault et al 2011), whereas C. stoebe can induce changes in the soil bacterial community to succeed (Thébault et al 2010). We experimentally established two types of artiWcial mixtures of intra-speciWcally aggregated and randomly dispersed resident plant species.…”