The Effects of Flavonoid Allelochemicals from Knapweeds on Legume–Rhizobia Candidates for Restoration

Abstract

Russian knapweed (Acroptilon repens) and Spotted knapweed (Centaurea maculosa) are allelopathic weeds invasive in North American grasslands. Both species contain at least one phytotoxic flavonoid root exudate with demonstrated negative influences on other plants. Previous findings indicated that Silky lupine (Lupinus sericeus), among other legumes, was relatively resistant to Spotted knapweed invasion and allelochemistry. We hypothesized that legume species may exhibit resistance to flavonoids in knapweed root exudates and may serve as candidate species for management efforts. Because legumes form symbiotic relationships with rhizobia, these bacteria must also be evaluated for allelochemical resistance before legumes can be recommended for restoration. In this study, we examined four legume species for effects of 7,8-benzoflavone (from Russian knapweed) and (±)-catechin (from Spotted knapweed) on rhizosphere interactions involving legume roots and associated rhizobia. Pure cultures of four rhizobia strains exhibited varied responses when grown with 7,8-benzoflavone or (±)-catechin. Alfalfa (Medicago sativa) and its bacterial symbiont, Sinorhizobium meliloti, exhibited allelochemical resistance that varied with (±)-catechin concentration when grown in vitro. Four legume species were grown under greenhouse conditions. Plants that were inoculated and nodulated generally exhibited no response to 7,8-benzoflavone or (±)-catechin treatments. Plants that were not inoculated exhibited stronger responses. Therefore, inoculation and nodulation may confer resistance to allelochemicals. These results, when coupled with previous research and field observations, suggest that legumes may not be susceptible to knapweed allelopathy and may be good choices in restoration of knapweed infestations when inoculated, particularly on sites with low soil nitrogen.

Acroptilon repens, an Asian invader, has stronger competitive effects on species from America than species from its native range

“…The North American species paired with C. intybus, G. aristata, germinated poorly and did not grow in any treatment and was excluded from analysis. Medicago sativa (alfalfa) has been reported to have allelopathic potential itself (AbdulRahman and Habib 1989) and to coexist with Acroptilon (Kulmatiski 2006;Alford et al 2008). Alford et al (2008) reported that M. sativa showed no response to 7,8-benzoflavone, one of the phytochemicals reported to have been isolated from Acroptilon roots, but Quintana et al (2008) were unable to confirm that the invader produces this chemical.…”

A novel impact of a novel weapon: allelochemicals in Alliaria petiolata disrupt the legume-rhizobia mutualism

“…Similarly, the invasive plant, Amaranthus viridis (green amaranth), reduced rhizobia growth in culture and nodulation when native Acacia legumes were grown in the presence of tissue extracts (Sanon et al 2009). In some cases, nodulation may actually protect native plants from allelopathic effects; legumes inoculated with rhizobia were unaffected by (±)-catechin treatments, while uninoculated plants experienced allelopathic effects (Alford et al 2009). …”

Shared and host‐specific microbiome diversity and functioning of grapevine and accompanying weed plants

“…Plant species investigated in this study show different root morphologies (Supporting Information Table S1), which are likely to influence resource uptake and the formation of an interaction with microbial communities (Bardgett et al ., ). Furthermore, plant growth stage (Rasche et al ., ; Micallef et al ., ), species‐specific root exudation patterns (Dennis et al ., ), input of litter with unique chemical properties (Ashton et al ., ), the release of secondary compounds (Callaway and Aschehoug, ) and production of allelochemicals (Alford et al ., ) could also contribute to the observed variances in bacterial community composition.…”