Soil Fungi and Phosphorus Unlock the Secret Behind a Prized Chinese Medicine’s Potency

For centuries, the dried fruits of Amomum villosum, known in traditional Chinese medicine as Fructus Amomi, have been prized for protecting the gastric mucosa, easing digestive complaints, relieving pain, and adding a distinctive aroma to foods across Southeast Asia. Yet not all Amomum is created equal. The finest quality comes from Yangchun City in China’s Guangdong province, the plant’s core geographical region, where the perennial herb of the ginger family reaches its full medicinal potential. Since the 1950s, growers have introduced the crop to Guangxi, Yunnan, Fujian, and other non-core regions to satisfy a market demand that Yangchun alone cannot meet, but the transplanted plants have produced raw materials of inconsistent quality. A new study published in the Journal of Advanced Research now offers a striking explanation for this geographic divide, tracing the difference not to climate or genetics alone but to an intricate underground partnership between the plant’s roots, soil phosphorus, and a phosphate-dissolving fungus called Penicillium citrinum.

The research team, led by Zhenkai Li and Hong Wu, began by comparing Amomum villosum plants from four production areas: the core region of Yangchun and three non-core regions in Zhanjiang, Liuzhou, and Xishuangbanna. Using sophisticated metabolomic platforms combining liquid chromatography and gas chromatography coupled with mass spectrometry, they identified a remarkable 2,570 metabolites across the samples, classified into 26 major chemical classes, with terpenoids, flavonoids, and phenolic acids dominating the profile. Statistical comparisons between Yangchun and each of the other regions revealed hundreds of differential metabolites, and terpenoids proved to be the most prevalent class among them. A Venn analysis pinpointed 82 metabolites that differed consistently across all three comparisons, and 11 of the 15 terpenoids among them were more abundant in Yangchun, signaling that this region somehow promotes a far greater accumulation of the compounds that matter most.

The compounds in question are the plant’s crown jewels. Bornyl acetate, borneol, and camphor are the principal functional substances of Amomum villosum, concentrated in its fruits and roots and intimately tied to both its aroma and its clinical efficacy. Bornyl acetate exhibits gastrointestinal antispasmodic, antidiarrheal, analgesic, and anti-inflammatory effects; borneol is valued for refreshing the mind, clearing heat, relieving pain, and showing antibacterial and neuroprotective activities; camphor is a clinical staple against itching and chilblains. When the researchers quantified these components directly, the pattern was unmistakable. Yangchun fruits contained 1.37 milligrams per gram of borneol and 13.65 milligrams per gram of bornyl acetate, both significantly higher than the non-core regions, while paradoxically carrying the lowest camphor content at 1.5 milligrams per gram, compared with 4.1 in Xishuangbanna. High camphor, it turns out, is not the mark of quality; the sweet spot lies in maximizing bornyl acetate and borneol.

To understand why Yangchun plants excel at producing these terpenoids, the team turned to transcriptomics, sequencing gene expression across all four regions and applying weighted gene co-expression network analysis to link genes with metabolites. The analysis flagged members of the BAHD gene family, a class of acyltransferases that attach acyl groups to terpenoids, as prime candidates for regulating bornyl acetate biosynthesis. One gene, WvBAHD3, showed a strong positive correlation with bornyl acetate levels, while a related gene, WvBAHD53, was expressed at levels too low to be meaningful. In a decisive functional test, the researchers used transient overexpression in Amomum leaves, dividing each leaf along its main vein so one half carried the gene and the other an empty vector control. When WvBAHD3 was overexpressed, both gene expression and bornyl acetate content rose significantly, confirming WvBAHD3 as a genuine molecular switch for the compound and giving the team a reliable indicator to track in subsequent experiments.

With the plant side mapped, the investigation moved underground. The researchers measured fifteen soil physicochemical indicators in rhizosphere samples from each region and found that Yangchun soils stood out for their exceptionally high levels of available phosphorus and available iron, reaching 21.52 and 112.27 milligrams per kilogram respectively. Intriguingly, total phosphorus and total iron showed no such advantage, suggesting that what distinguishes Yangchun is not the sheer quantity of these elements but their chemical form and ease of release. Principal component analysis cleanly separated Yangchun from the other regions, with available phosphorus and available iron emerging as the most critical indicators. This distinction matters because in the acidic soils of southern China, phosphorus readily locks into insoluble complexes with iron and aluminum, and roughly seventy percent of arable soils worldwide face phosphorus deficiency, with plant-available phosphorus accounting for only four to five percent of the total.

Metagenomic sequencing of the rhizosphere microbial communities added a third dimension to the picture. The analysis annotated more than 46,000 microbial species across the four regions and revealed that the roots of Amomum villosum actively recruit specific beneficial taxa. Twelve microbial genera were significantly enriched in Yangchun’s rhizosphere, and correlation analysis showed that three of them, Penicillium, Limnoraphis, and Alcaligenes, were significantly associated with all three major bioactive components. Crucially, these genera were absent from the list of Yangchun-enriched bulk soil microbes, indicating that the plant itself, through its root characteristics, specifically recruits them from the surrounding soil. A Mantel test weaving together microbes, soil chemistry, and metabolites confirmed a tight web of positive correlations linking Penicillium, available phosphorus, available iron, and the levels of borneol and bornyl acetate, while camphor showed negative associations with the same factors.

The team then ran a series of elegant validation experiments. Seedlings grown in Yangchun soil under identical conditions to those in Zhanjiang soil grew more vigorously, developed more robust roots, and accumulated significantly more borneol and bornyl acetate. Plants raised in sterilized Yangchun soil produced less of these compounds than those in unsterilized soil, and seedlings in sterile laboratory medium produced almost no terpenoids at all, proving that living soil microbes are indispensable for bioactive compound accumulation. Four Penicillium species were isolated from Yangchun rhizosphere soil, and the researchers focused on Penicillium citrinum, the only one also detected in the metagenomic data. When potted plants received biweekly applications of P. citrinum suspension, a moderate dose at an optical density of 0.2 proved optimal, raising borneol to 0.21 milligrams per gram and bornyl acetate to 0.48 milligrams per gram in the roots, while simultaneously upregulating WvBAHD3 expression.

Phosphorus supplementation experiments completed the mechanistic chain. Applying calcium dihydrogen phosphate to low-phosphorus Zhanjiang soil boosted borneol and bornyl acetate in the roots, with moderate doses performing best, and field trials on mature fruit-bearing plants confirmed that phosphorus fertilizer significantly increased these compounds in the actual fruits. Iron supplementation, by contrast, had no significant effect, marking available phosphorus as the decisive soil factor. The fungus earned its keep through a remarkable chemistry trick: in culture medium with insoluble tricalcium phosphate or iron phosphate as the sole phosphorus source, P. citrinum gradually dissolved the minerals, lowered the pH, and released available phosphorus and iron. Mass spectrometry of its secretions revealed 80 fungus-specific metabolites, including organic acids such as malic acid and succinic acid, which are likely the primary agents of this phosphate-solubilizing activity. When insoluble calcium phosphate was co-applied with P. citrinum in soil, the combination restored available phosphorus levels and boosted borneol and bornyl acetate just as effectively as soluble phosphorus alone.

The implications ripple outward from a single herb. The study demonstrates that the superior quality of Yangchun Amomum villosum rests on a three-way interplay among soil phosphorus availability, a specifically recruited rhizosphere fungus, and the plant’s own terpenoid biosynthesis genes. It also hints at a subtle trade-off: at high phosphorus doses, compound contents and gene expression declined even as plant growth improved, suggesting the plant may prioritize development over secondary metabolism when nutrients are abundant. Because many rhizosphere microbes resist laboratory culture, the roles of Alcaligenes and Limnoraphis remain unverified, and the authors acknowledge that additional microorganisms almost certainly participate in the full effect. Still, the findings open a practical path forward: managing soil phosphorus and deploying beneficial Penicillium strains as microbial agents could help growers in non-core regions close the quality gap, while synthetic microbial communities assembled from complementary beneficial species may one day restore degraded soils and elevate the medicinal potency of crops far beyond this one aromatic fruit.

Subject of Research: Rhizosphere microbiome and soil phosphorus regulation of terpenoid bioactive compound accumulation in the medicinal plant Amomum villosum

Article Title: Rhizosphere Penicillium and phosphorus availability drive bioactive compound accumulation in Amomum villosum

Article References: Li, Z., Qin, Y., Cai, J., Luo, X., Yao, Y., Wang, Y., Liang, Q., Xie, L., Bai, M., Liang, X., Liang, C., He, J., & Wu, H. (2026). Rhizosphere Penicillium and phosphorus availability drive bioactive compound accumulation in Amomum villosum. Journal of Advanced Research. https://doi.org/10.1016/j.jare.2026.10.030

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.10.030

Keywords: Amomum villosum, Penicillium citrinum, rhizosphere microbiome, phosphorus solubilization, bornyl acetate, borneol, secondary metabolites, terpenoids, WvBAHD3, medicinal plants, soil microbiology, transcriptomics