Diversity and structure of soil nematode communities under Heracleum sosnowskyi pressure: latitudinal and invasion-driven variations

Summary

Soil nematode communities under invasion by Heracleum sosnowskyi Manden. (Sosnowsky’s hogweed) were studied in habitats of different latitudinal locations. The research was conducted in four hogweed sites located between 61° and 55° N, in the Republic of Karelia (Shuya and Essoila villages), and the Leningrad and Moscow Regions. Soil samples were collected beneath dense H. sosnowskyi stands and in adjacent control meadows that were not invaded. The structure of soil nematode communities in hogweed habitats was characterised by the dominance of omnivorous nematodes and plant-associated nematodes (Shuya village), as well as bacterial feeders and omnivores (Essoila village) in Karelia; by a high proportion of bacterial feeders and plant parasites in the Leningrad Region; and by the dominance of bacterial and fungal feeders in the Moscow Region. Plant invasion altered the ratio of trophic groups in the nematode communities: statistically significant changes were detected in the abundance of bacterial feeders (increased under hogweed), fungal feeders, and plant-associated nematodes (both decreased under hogweed). However, the total number of identified nematode taxa remained almost unchanged, indicating that the introduction of a non-native plant species into local ecosystems did not lead to a substantial decrease in diversity of soil nematodes. RDA analysis showed that the studied abiotic and biotic factors – habitat type (hogweed/meadow) as an indicator of invasion impact, pH, total carbon and nitrogen, available phosphorus, and potassium – had a significant influence on nematode community parameters. The combination of these factors explained about 50% of the variation in nematological characteristics. Notably, latitude had no significant effect on the overall variability of nematode indices, emphasising the predominance of invasion effects over geographic position.