Can Arbuscular Mycorrhizal Fungi Reduce the Growth of Agricultural Weeds?

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) are known for their beneficial effects on plants. However, there is increasing evidence that some ruderal plants, including several agricultural weeds, respond negatively to AMF colonization. Here, we investigated the effect of AMF on the growth of individual weed species and on weed-crop interactions. METHODOLOGY/PRINCIPAL FINDINGS: First, under controlled glasshouse conditions, we screened growth responses of nine weed species and three crops to a widespread AMF, Glomus intraradices. None of the weeds screened showed a significant positive mycorrhizal growth response and four weed species were significantly reduced by the AMF (growth responses between -22 and -35%). In a subsequent experiment, we selected three of the negatively responding weed species--Echinochloa crus-galli, Setaria viridis and Solanum nigrum--and analyzed their responses to a combination of three AMF (Glomus intraradices, Glomus mosseae and Glomus claroideum). Finally, we tested whether the presence of a crop (maize) enhanced the suppressive effect of AMF on weeds. We found that the growth of the three selected weed species was also reduced by a combination of AMF and that the presence of maize amplified the negative effect of AMF on the growth of E. crus-galli. CONCLUSIONS/SIGNIFICANCE: Our results show that AMF can negatively influence the growth of some weed species indicating that AMF have the potential to act as determinants of weed community structure. Furthermore, mycorrhizal weed growth reductions can be amplified in the presence of a crop. Previous studies have shown that AMF provide a number of beneficial ecosystem services. Taken together with our current results, the maintenance and promotion of AMF activity may thereby contribute to sustainable management of agroecosystems. However, in order to further the practical and ecological relevance of our findings, additional experiments should be performed under field conditions

Stressed out symbiotes:hypotheses for the influence of abiotic stress on arbuscular mycorrhizal fungi

Abiotic stress is a widespread threat to both plant and soil communities. Arbuscular mycorrhizal (AM) fungi can alleviate effects of abiotic stress by improving host plant stress tolerance, but the direct effects of abiotic stress on AM fungi are less well understood. We propose two hypotheses predicting how AM fungi will respond to abiotic stress. The stress exclusion hypothesis predicts that AM fungal abundance and diversity will decrease with persistent abiotic stress. The mycorrhizal stress adaptation hypothesis predicts that AM fungi will evolve in response to abiotic stress to maintain their fitness. We conclude that abiotic stress can have effects on AM fungi independent of the effects on the host plant. AM fungal communities will change in composition in response to abiotic stress, which may mean the loss of important individual species. This could alter feedbacks to the plant community and beyond. AM fungi will adapt to abiotic stress independent of their host plant. The adaptation of AM fungi to abiotic stress should allow the maintenance of the plant-AM fungal mutualism in the face of changing climates. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00442-016-3673-7) contains supplementary material, which is available to authorized users

Nitrogen fixation ability explains leaf chemistry and arbuscular mycorrhizal responses to fertilization

Atmospheric nitrogen (N) and phosphorus (P) deposition rates are predicted to drastically increase in the coming decades. The ecosystem level consequences of these increases will depend on how plant tissue nutrient concentrations, stoichiometry and investment in nutrient uptake mechanisms such as arbuscular mycorrhizal fungi (AMF) change in response to increased nutrient availability, and how responses differ between plant functional types. Using a factorial nutrient addition experiment with seedlings of multiple N-fixing and non-N-fixing tree species, we examined whether leaf chemistry and AMF responses differ between these dominant woody plant functional groups of tropical savanna and dry forest ecosystems. We found that N-fixers have remarkably stable foliar chemistry that stays constant with external input of nutrients. Non-N-fixers responded to N and N + P addition by increasing both concentrations and total amounts of foliar N, but showed a corresponding decrease in P concentrations while total amounts of foliar P stayed constant, suggesting a ‘dilution’ of tissue P with increased N availability. Non-N-fixers also showed an increase in N:P ratios with N and N + P addition, probably driven by both an increase in N and a decrease in P concentrations. AMF colonization decreased with N + P addition in non-N-fixers and increased with N and N + P addition in N-fixers, suggesting differences in their nutrient acquisition roles in the two plant functional groups. Our results suggest that N-fixers and non-N-fixers can differ significantly in their responses to N and P deposition, with potential consequences for future nutrient and carbon cycling in savanna and dry forest ecosystems

Mycorrhizal fungi suppress aggressive Agricultural weeds.

Plant growth responses to arbuscular mycorrhizal fungi (AMF) are highly variable, ranging from mutualism in a wide range of plants, to antagonism in some non-mycorrhizal plant species and plants characteristic of disturbed environments. Many agricultural weeds are non mycorrhizal or originate from ruderal environments where AMF are rare or absent. This led us to hypothesize that AMF may suppress weed growth, a mycorrhizal attribute which has hardly been considered. We investigated the impact of AMF and AMF diversity (three versus one AMF taxon) on weed growth in experimental microcosms where a crop (sunflower) was grown together with six widespread weed species. The presence of AMF reduced total weed biomass with 47% in microcosms where weeds were grown together with sunflower and with 25% in microcosms where weeds were grown alone. The biomass of two out of six weed species was significantly reduced by AMF (-66% & -59%) while the biomass of the four remaining weed species was only slightly reduced (-20% to -37%). Sunflower productivity was not influenced by AMF or AMF diversity. However, sunflower benefitted from AMF via enhanced phosphorus nutrition. The results indicate that the stimulation of arbuscular mycorrhizal fungi in agro-ecosystems may suppress some aggressive weeds