Woody and herbaceous invasive alien plant species-derived biochars are potentially optimal for soil amendment, soil remediation, and carbon storage

Invasive alien plant species (IAPS) are a global problem, representing a threat to ecosystem functioning, biodiversity, and human health. Legislation requires the management and eradication of IAPS populations; yet, management practices are costly, require several interventions, and produce large amounts of waste biomass. However, the biomass of eradicated IAPS can become a resource by being used as feedstock for biochar production and, at the same time, implementing the management of IAPS. Here we carried out an in-depth characterization of biochar produced at 550°C derived from 10 (five woody and five herbaceous) widespread IAPS in the central-southern Alps region to determine their potential applications for soil amendment, soil remediation, and carbon storage. Biochar was produced at a laboratory scale, where its physicochemical characteristics, micromorphological features, and lead adsorption from aqueous solutions were measured. To investigate any possible trade-offs among the potential biochar applications, a principal component analysis was performed. IAPS-derived biochars exhibited relevant properties in different fields of application, suggesting that IAPS biomass can be exploited in a circular economy framework. We found coordinated variation and trade-offs from biochars with high stability to biochars with high soil amendment potential (PC1), while the biochar soil remediation potential represents an independent axis of variation (PC2). Specifically, IAPS-derived biochar had species-specific characteristics, with differences between the woody and herbaceous IAPS, the latter being more suitable for soil amendment due to their greater pH, macronutrient content, and macropore area. Biochar derived from woody IAPS showed a greater surface area, smaller pores, and had higher lead adsorption potentials from aqueous solutions, hinting at their higher potential for heavy metal pollution remediation. Moreover, biochar derived from woody IAPS had a higher fixed carbon content, indicating higher carbon stability, and suggesting that their biochar is preferable for carbon sequestration in the view of climate change mitigation.