Impact of Gleditsia triacanthos L. (Fabaceae) on nematode community composition in South African grassland

The relationship between invasive alien plants and nematodes remains understudied. Nematodes play a significant role in soil food webs and have a high functional diversity. Invasive plants cause shifts in the community structure of the fauna and flora in the areas they invade; therefore, they have the potential to also cause shifts in the nematode communities in the soil surrounding their roots. This study investigated whether nematode species composition and trophic structure differed between grasslands invaded by Gleditsia triacanthos (honey locust) and uninvaded grasslands, and whether these patterns varied across seasons. Samples were collected from five grassland sites in the Free State Province, South Africa, over a four season period. A total of 235,605 individual nematodes, belonging to 25 families and 59 species or morphospecies, were identified across all sites and seasons. Both invasion and season significantly influenced nematode community composition in all locations except for one site, where only season had a significant effect. Herbivorous, bacterivorous and fungivorous nematodes contributed most to the dissimilarity and were significantly more abundant in invaded grasslands, where enrichment was also generally higher. Predatory and omnivorous nematodes were more common in uninvaded grasslands. Uninvaded grasslands also exhibited higher species diversity, evenness, and higher structure and maturity indices, although these varied seasonally. These findings show that G. triacanthos alters nematode diversity and community composition, and that these changes are also shaped by seasonal dynamics. This shift may have implications for the belowground functioning of grasslands.