Feremycorrhiza (FM) is a newly discovered plant-fungus symbiosis that improves plant growth and nutrition without development of interface structures (i.e. no root colonization). The host plant range in the FM symbiosis is currently unknown. We report the results of controlled environment investigations characterizing the capability of crops to establish FM symbiosis with Austroboletus occidentalis, along with comprehensive in vitro studies to unravel the functional mechanisms underlying the phosphorus (P) nutritional benefits conferred to host plants. After 16 weeks of growth in a natural low-nutrient field soil (containing indigenous microbes), two mycorrhizal crops [wheat (Triticum aestivum) and barley (Hordeum vulgare)], and the non-mycorrhizal crop canola (Brassica napus) inoculated with A. occidentalis had significantly higher shoot biomass compared to the control (non-inoculated) plants. The FM symbiosis also led to significant grain yield increases in wheat (by 54%) and barley (by 37%) compared to the control plants, while canola was harvested before setting seeds due to slow growth under nutrient deficiency. In all crops, the FM symbiosis significantly improved the shoot nutrient content, including that of P, potassium and magnesium. Total nitrogen accumulation (shoot + grain content) was also significantly higher in all inoculated vs control crops. Inoculated treatments had reduced soil pH compared to the control, which was attributed to fungal activities in soil, leading to greater nutrient (P, in particular) availability to host plants. Presence of A. occidentalis in soil did not affect root colonization by indigenous arbuscular mycorrhizal fungi in wheat and barley, and no root colonization was detected in canola. Our in vitro studies demonstrated the solubilization, by A. occidentalis, of the water-insoluble P forms, including calcium phosphate (CaP, as hydroxyapatite), iron phosphate (FePO₄), and aluminium phosphate (AlPO₄) via exudation of organic acid anions (mainly oxalate, along with citrate and fumarate). The ³¹P nuclear magnetic resonance (NMR) spectroscopy revealed the presence of similar P species (dominated by orthophosphate and long-chain inorganic polyphosphates) in the agar-based media supplemented with different P forms (KH₂PO₄, CaP, FePO₄ or AlPO₄), indicating that all three water-insoluble P compounds were solubilized and transformed by the FM fungus. Furthermore, our in vitro studies revealed that the FM fungus converted a large proportion of the solubilized P (free orthophosphate) into long-chain inorganic polyphosphates (making up to 51% of total P in the media). The results demonstrated that the three important grain crops, regardless of their capacity to support arbuscular mycorrhizae, could get the growth and nutritional benefits from the FM symbiosis, emphasizing the potential of A. occidentalis as a novel fungal biofertilizer for agricultural crops.

Feremycorrhiza（FM）是一种新发现的植物-真菌共生植物，可提高植物的生长和营养，而不会形成界面结构（即无根定植）。FM共生的寄主植物范围目前未知。我们报告了受控环境调查的结果，这些调查结果表征了农作物与西方小菜蛾建立FM共生的能力，并进行了全面的体外研究，以揭示赋予宿主植物磷（P）营养益处的功能机制。在天然的低营养田地土壤（包含本地微生物）中生长16周后，有两种菌根作物[小麦（Triticum aestivum）和大麦（Hordeum vulgare））]，而接种西洋曲霉的非菌根农作物低芥酸菜籽（Brassica napus）与对照（未接种）植物的茎生物量明显较高。与对照植物相比，FM共生还导致小麦（增加54％）和大麦（增加37％）的谷物单产显着增加，而由于在营养缺乏的情况下生长缓慢，在固定种子之前收获了双低油菜籽。在所有作物中，FM共生都显着提高了枝条的养分含量，包括P，钾和镁。与所有接种相比，总氮积累量（芽＋籽粒含量）也明显更高控制农作物。与对照相比，接种处理的土壤pH值降低，这归因于土壤中的真菌活性，导致寄主植物养分（尤其是磷）的利用率更高。在土壤中存在西洋曲霉不会影响小麦和大麦中本地丛枝菌根真菌的根部定植，并且在双低油菜籽中未检测到根部定植。我们的体外研究表明，水不溶性P形式可通过A. occidentalis溶解，包括磷酸钙（CaP，作为羟基磷灰石），磷酸铁（FePO ₄）和磷酸铝（AlPO ₄）。阴离子（主要是草酸盐，以及柠檬酸盐和富马酸盐）。在³¹P核磁共振（NMR）光谱显示，在琼脂基培养基中补充了不同的P形式（KH ₂ PO ₄，CaP，FePO ₄或AlPO ₄）后，存在相似的P物质（以正磷酸盐和长链无机多磷酸盐为主）），表明这三种水不溶性P化合物均被FM真菌溶解并转化。此外，我们的体外研究表明，FM真菌将大部分溶解的P（游离正磷酸盐）转化为长链无机多磷酸盐（占培养基中总P的51％）。结果表明，三种重要的谷物作物，不管它们支持丛枝菌根的能力如何，都可以从FM共生中获得生长和营养益处，从而强调了A. occidentalis作为新型农作物真菌生物肥料的潜力。