Direct and Indirect Effects on Soil Nematode Communities Differ Between Facilitative and Allelopathic Plants

Plants are expected to affect soil nematode communities. However, comparative studies on the direct and indirect ways dominant plants influence soil nematode communities are rare. In this study, we compared the effects of a dominant allelopathic plant, Ligularia virgaurea, and a dominant facilitative plant, Dasiphora fruticosa, on soil nematode richness and community composition in an alpine meadow of the Tibetan plateau. Our result indicated that 1) D. fruticosa significantly increased nematode richness whereas L. virgaurea had no significant effect; 2) D. fruticosa had no significant impact on bacterial and fungal richness, but L. virgaurea increased fungal richness; 3) D. fruticosa had strong positive direct, and weak positive indirect, effects on nematode richness, mainly mediated by a marginal decrease in fungal richness. By contrast, L. virgaurea had no significant direct effect on soil nematode richness but had strong indirect effects, mainly mediated by changes in soil pH and soil organic carbon content; 4) L. virgaurea influenced soil nematode community composition predominantly through direct effects but also indirectly through soil organic carbon. By contrast, D. fruticosa affected nematode communities through changes in understory plant communities, soil physiochemical, and microbial communities. Both facilitative and allelopathic plants thus influence soil nematode richness and community composition but seemingly in different ways. These highlight the importance of plants in determining soil community diversity and provide new insight to disentangle the complex above- and belowground linkages.

Influence of Asclepias syriaca on soil nematode communities

The main goal of this study was to evaluate the impact of the invasive common milkweed (Asclepias syriaca L.) on soil nematode communities. The research was carried out in 2018 and 2019 in an ecosystem of permanent grassland in the basin of the Laborec River in land registries of Drahňov, a Vojany village in southeastern Slovakia. The ecosystem contained a total of 64 species of free-living and parasitic nematodes. The most prevalent trophic groups were bacterial feeders (Acrobeloides nanus), followed by plant parasites (Helicotylenchus digonicus and Pratylenchus pratensis), fungal feeders (Aphelenchus avenae), and omnivores (Eudorylaimus carteri). The number of nematode species, the composition of trophic groups and the structure of communities in areas with invasive plants were similar to those in areas with native vegetation during the two years of observation.