Insights into the ecological mechanisms of Conyza canadensis invasion in heavy metal-contaminated soil.

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conclusionSoil nutrients and associated bacterial shifts revealed that positive plant-soil feedback enables Conyza canadensis to colonize metal-contaminated soil. The identified thresholds provide guidance for effective weed management under environmental stress. Invasion by non-native plants can trigger a self-promoting mechanism that facilitates their invasion by affecting soil nutrients and microbiota. Notably, the invasive Conyza canadensis (L.) Cronquist tends to colonize metal-contaminated areas. This study investigated how its progressive invasion affected abiotic and biotic properties in cadmium (Cd) and lead (Pb) co-contaminated soil. Different invasion stages were simulated by varying the relative densities of C. canadensis and the non-invasive Lactuca indica Linn. Both abiotic and biotic components were significantly altered as the invasion intensity increased. Along the invasion gradient of C. canadensis, the soil contents of total phosphorus (TP), available phosphorus (AP), available potassium (AK), and soil organic matter (SOM), the structure of soil bacterial communities, and the accumulation of heavy metals in plant roots were altered. The relative abundances of key bacterial taxa associated with nutrient cycling, such as the phyla Gemmatimonadota and Planctomycetota, and the families Gemmatimonadaceae, Burkholderiaceae, Micrococcaceae, and Sphingomonadaceae, were shifted. Importantly, critical thresholds for abrupt nutrient shifts were identified through the discontinuous changes of AK and AP when C. canadensis invasion levels reached 38% and 48%, respectively. These nutrient thresholds coincided with shifts in the relative abundance of bacterial taxa involved in nutrient cycling, such as Micrococcaceae (OTU68) and Solibacteraceae (OTU208). The triggering of changes in the abiotic and biotic components of the soil system may represent crucial functional traits that promote positive feedbacks to increase the invasiveness of C. canadensis. These interactions support the ecological dynamics and successful colonization of C. canadensis in heavy metal-contaminated soil, and the identified invasion thresholds can provide guidance for effective weed management under environmental stress.