Abstract
A controlled-environment study was conducted to explore possible synergistic interactions between the feremycorrhizal (FM) fungus Austroboletus occidentalis and soil free-living N2-fixing bacteria (diazotrophs). Wheat (Triticum aestivum) plants were grown under N deficiency conditions in a field soil without adding microbial inoculum (control: only containing soil indigenous microbes), or inoculated with a consortium containing four free-living diazotroph isolates (diazotrophs treatment), A. occidentalis inoculum (FM treatment), or both diazotrophs and A. occidentalis inoculums (dual treatment). After 7 weeks of growth, significantly greater shoot biomass was observed in plants inoculated with diazotrophs (by 25%), A. occidentalis (by 101%), and combined inoculums (by 106%), compared to the non-inoculated control treatment. All inoculated plants also had higher shoot nutrient contents (including N, P, K, Mg, Zn, Cu, and Mn) than the control treatment. Compared to the control and diazotrophs treatments, significantly greater shoot N content was observed in the FM treatment (i.e., synergism between the FM fungus and soil indigenous diazotrophs). Dually inoculated plants had the highest content of nutrients in shoots (e.g., N, P, K, S, Mg, Zn, Cu, and Mn) and soil total N (13–24% higher than the other treatments), i.e., synergism between the FM fungus and added diazotrophs. Root colonization by soil indigenous arbuscular mycorrhizal fungi declined in all inoculated plants compared to control. Non-metric multidimensional scaling (NMDS) analysis of the bacterial 16S rRNA gene amplicons revealed that the FM fungus modified the soil microbiome. Our in vitro study indicated that A. occidentalis could not grow on substrates containing lignocellulosic materials or sucrose, but grew on media supplemented with hexoses such as glucose and fructose, indicating that the FM fungus has limited saprotrophic capacity similar to ectomycorrhizal fungi. The results revealed synergistic interactions between A. occidentalis and soil free-living diazotrophs, indicating a potential to boost microbial N2 fixation for non-legume crops.
Highlights
The Australian native fungus Austroboletus occidentalis (Boletaceae, Basidiomycota) establishes feremycorrhizal (FM) symbiosis, conferring significant growth and nutritional benefits to diverse host plants, including the Australian native plant jarrah (Eucalyptus marginata) (Kariman et al 2012, 2014), mycorrhizal crops such as wheat (Triticum aestivum) and barley (Hordeum vulgare), as well as the non-mycorrhizal crop canola (Brassica napus) (Kariman et al 2020)
The present study was conducted to (i) explore the potential of the FM fungus A. occidentalis, alone or in combination with free-living diazotrophs consortium, to improve growth and N nutrition of wheat plants grown under N deficiency conditions, (ii) characterize soil chemical/microbial factors linked with symbiotic N nutritional benefits to host plants via assessing soil N forms (NO3−-N, NH4+-N, and total N) and changes in soil microbial composition, and (iii) determine the capacity of A. occidentalis to utilize different sugars and lignocellulosic substrates as a food source in vitro
Jars were placed under a laminar flow to cool down, and each jar was inoculated with 10 hyphal plugs (5 mm in diameter) taken from the 6-week-old fungal colonies growing on potato dextrose agar (PDA) plates at 20 °C
Summary
The Australian native fungus Austroboletus occidentalis (Boletaceae, Basidiomycota) establishes feremycorrhizal (FM) symbiosis, conferring significant growth and nutritional benefits to diverse host plants, including the Australian native plant jarrah (Eucalyptus marginata) (Kariman et al 2012, 2014), mycorrhizal crops such as wheat (Triticum aestivum) and barley (Hordeum vulgare), as well as the non-mycorrhizal crop canola (Brassica napus) (Kariman et al 2020). In contrast to all known mycorrhizal/endophytic associations, in FM symbiosis, fungal hyphae do not colonize plant roots (Kariman et al 2014, 2018, 2020). A direct intraradical nutrient exchange between host plants and fungal partners occurs in AM/ECM symbioses, but not in the FM symbiosis due to lack of root colonization; both FM and ECM symbioses exhibit organic acid anion-mediated nutrient solubilization (Kariman et al 2014, 2020). The nutritional benefits of the FM symbiosis are attributed primarily to the fungal role in rhizosphere modification and nutrient solubilization/ mobilization (Kariman et al 2014, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
