A research team from the Kunming Institute of Botany of the Chinese Academy of Sciences (CAS) has developed a two-stage bioconversion system that transforms Ageratina adenophora, one of China's most destructive invasive plants, into a valuable biofertilizer.

Commonly known as crofton weed, A. adenophora is responsible for an estimated annual economic loss of around 3.62 billion RMB to Chinese agriculture and grassland ecosystems. It releases toxic sesquiterpenes, such as dehydrotremetone (DTD) and 9-oxo-10,11-dehydroageraphorone (HHO), that severely disrupt native ecosystems, inhibit livestock grazing and reduce agricultural productivity. Conventional disposal methods, such as open burning or landfill, often generate secondary pollution while failing to recover valuable biomass resources.

To address these challenges, the researchers established an innovative "composting pre-detoxification—black soldier fly (BSF) larval conversion" system, this dual-phase bioconversion process enables sequential detoxification and quality enhancement.

In the first phase, the aerobic composting of A. adenophora for 56 days removed more than 89% of toxic sesquiterpenes, with DTD levels dropping from approximately 2,000 to 220.8 mg/kg and HHO from around 700 to 96.4 mg/kg. Metagenomic analysis revealed an increase in the abundance of Proteobacteria, Actinobacteriota and Bacteroidota, with Bacillus reaching 32.4%.

These taxa drive toxin degradation via co-metabolic pathways, while lignin peroxidase and laccase activities increased 5.8–8.9-fold, enhancing lignocellulose decomposition and humification (humic acid: 35.9 vs. 16.1 g/kg in controls).

The composting process simultaneously mitigated multiple risks. Bioavailable heavy metals such as copper, zinc, chromium, and lead declined by 73.9–97.9% through microbial biosorption and humic complexation. Pathogens—including Xanthomonas, Staphylococcus, and Salmonella—as well as key antibiotic resistance genes were reduced by more than 90%, while multidrug efflux genes decreased by over 75%. Mantel tests confirmed phytochemistry-driven "microbial regulation—chemical fixation—biological stabilization" synergies.

In addition, the system demonstrated strong climate and nutrient benefits. Incorporating A. adenophora at 7.5–10% suppressed methane emissions to undetectable levels by day 35 and reduced peak nitrous oxide emissions by 52.2%. Functional genes showed increased nitrogen fixation (nifH: 13.4%) and nitrification (amoA: 70.1%), but decreased denitrification (nirK/S and nosZ), reconstructing nitrogen metabolism and reducing gaseous losses. Nutrient enrichment was substantial: total nitrogen increased 2.15-fold (2.94 g/kg), phosphorus 15.6-fold (1.40 g/kg), and potassium 7.5-fold (3.21 g/kg), with germination indices of 98.9%.

The second phase employs black soldier fly larvae for further bioconversion. The larvae achieved additional detoxification, reducing DTD and HHO by 65.2% and 63.5%, respectively, bringing total detoxification to over 96%. Notably, larval growth was enhanced, with a 70% increase in weight. This stage also further reduced exchangeable cadmium and lead by 67% and 54%, respectively, while increasing total nitrogen and potassium by 30% and 8%, respectively. It also stabilized organic matter and lowered greenhouse gas emissions and odorous volatile compounds.

Together, these stages offer the first comprehensive explanation of the synergistic interaction between Ageratina adenophora, microbes, and black soldier flies. The composting phase achieves toxicity degradation, heavy metal passivation, pathogen elimination, and greenhouse gas reduction through phytochemistry-driven microbial community restructuring. The black soldier fly phase completes secondary detoxification via gut microbial co-metabolism. Bioturbation enhances nutrient concentration and risk management. This two-phase approach establishes a comprehensive technical chain for utilizing invasive plants.

Compared with traditional methods such as composting, incineration, or landfilling, this new system offers three major advantages. It ensures comprehensive risk mitigation through dual detoxification and pollutant control; produces a high-value biofertilizer suitable for applications ranging from edible fungi cultivation to organic vegetables and specialty fruits; and relies on relatively simple, locally adaptable processes, making it particularly suitable for regions heavily affected by A. adenophora, despite remaining collection cost challenges.

This study was supported the National Key Research and Development Program of China, the Strategic Priority Research Program of CAS, the Yunnan Province Caiyun Postdoctoral Program, and the Yunnan Provincial Technology Innovation Program.