Abstract
Rhizophagus intraradices, one of the common arbuscular mycorrhizal fungi (AMF) grown in the roots ofFlaveria bidentis, facilitates the invasion of this exotic plant species into China. However, it is still unknown whether nutrient transfer through the common mycorrhizal networks (CMN) between this exotic species and the native species enhances the competitive growth ofF. bidentisover the native species. To elucidate this question and the related mechanism, an isotopic labeling technique was used to test the transfer of carbon (C) and nitrogen (N) by CMN. Native species likeSetaria viridisandEclipta prostratawere selected to compete withF. bidentisin a polyvinyl chloride (PVC) box. Two competitive groups (F. bidentis-S. viridisandF. bidentis-E. prostrata), three treatments (monoculture ofF. bidentis, the mixture ofF. bidentisand the native plant, and the monoculture of the native plant), and two levels of AMF (presence or absence) were assigned. Results showed that the corrected index of relative competition intensity (CRCI) ofF. bidentisin the presence of AMF < 0 suggests that the competition facilitated the growth ofF. bidentiswith eitherS. viridisorE. prostrata. The reason was that the inoculation ofR. intra radicessignificantly increased the C and N contents ofF. bidentisin the mixtures. However, the effects ofR. intra radiceson the two native species were different: negative effect on the growth ofS. viridisand positive effect on the growth ofE. prostrata. The change of N content inS. viridisorE. prostratawas consistent with the variation of the biomass, suggesting that the N uptake explains the effects ofR. intraradiceson the competitive interactions betweenF. bidentisand the two native species. Moreover, the transfer of C and NviaAMF hyphal links did occur betweenF. bidentisand the native species. However, the transfer of C and N by the CMN was not positively related to the competitive growth ofF. bidentis.
Highlights
Arbuscular mycorrhizal fungi (AMF), an ecologically and economically important fungal guild, usually establish mutualistic associations with the majority of exotic plants (Bunn et al, 2015)
The mycorrhizal colonization of R. intraradices on S. viridis was significantly lower when it competed with F. bidentis than that when it was grown in the monoculture treatment [F(1, 18) = 36.470, P < 0.001] (Figure 2A)
The mycorrhizal colonization of R. intraradices on E. prostrata was significantly higher when it competed with F. bidentis than that when it was grown in the monoculture treatment [F(1, 18) = 204.833, P < 0.001] (Figure 2B)
Summary
Arbuscular mycorrhizal fungi (AMF), an ecologically and economically important fungal guild, usually establish mutualistic associations with the majority of exotic plants (Bunn et al, 2015). Some studies indicated that AMF colonization of the exotic species was usually higher than that of the native species. Other studies showed that the symbiotic relationship between the native plants and the AMF could be changed by the invasion of the exotic species (Callaway et al, 2008; Lekberg et al, 2013; Bunn et al, 2015). The changes in the mutualistic associations might lead to an increase (i.e., positive feedback) in the relative growth rate of the exotic species and a decrease (i.e., negative feedback) in the relative growth rate of the native species (Bever, 2002; Stinson et al, 2006; Pringle et al, 2009)
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