Soil nematode communities in riverbanks non-invaded and invaded by Fallopia japonica across diverse environmental conditions

Soil nematode communities are one of the most used bioindicators for assessing soil health and soil conditions. However, they are dependent on the presence of plants, some of which, known as 'invasive', affect local biodiversity when established. This study aimed to compare the communities of soil nematodes in riverbanks non-invaded and invaded by Fallopia japonica at three sites characterised by different environmental conditions. Our findings indicated that the ecosystem had a larger impact on the nematode communities than did the environmental variability at the study sites. Soil properties, such as pH, moisture content and organic-carbon content, differed significantly amongst the sites, but the nematode communities remained similar. Organic-carbon content was lower, and soil pH was higher, in the ecosystem with invasive F. japonica. Total nematode abundance, the abundances of fungivores, herbivores, omnivores and predators, and the maturity indices were significantly lower with invasive F. japonica. Fungivorous nematodes are essential for breaking down organic matter and releasing nutrients. Herbivorous nematodes respond to changes in the vegetation, and omnivorous and predatory nematodes contribute to the overall biodiversity and ecological balance in the soil ecosystem, so their lower abundance suggests a disturbance in the soil food web. The lower maturity indices suggested a disturbance or degradation of the soil ecosystem, which could have secondary negative effects on plant growth, nutrient availability and ecosystem resilience. These findings indicate that invasion both decreased the abundance of important soil organisms and disrupted the cycling of nutrients, potentially leading to long-term negative consequences for the invaded ecosystems. Understanding and managing the effects of invasive plants such as F. japonica are crucial for preserving soil health and promoting sustainable ecosystem functioning.