Nematodes and the effect of seasonality in grassland habitats of South Africa

Nematodes in South Africa have mainly been studied for their diversity and agricultural importance. However, the ecological status of nematodes and the effect of seasonal variation in local grasslands remain unknown. For this reason, a nematode study was conducted in the Telperion Nature Reserve and represented the first ecological study in a natural grassland area in South Africa. In total, 104 soil samples were collected during four consecutive seasons from 2015 until 2016 in three habitats, viz. (i) open grassland, (ii) shrubland with rocky outcrops, and (iii) riparian zone. From these the nematode community structure and soil ecosystem status were studied. In total, 93 genera from 50 families were recorded with herbivores and bacterivores being the most abundant trophic groups in all three habitats. Linear mixed models revealed that season had an overwhelmingly dominant impact on the condition, food web status, and functioning of the soil ecosystems with pairwise comparisons indicating that significantly higher values were recorded during winter. Interestingly, this seasonal shift can largely be attributed to fluctuations in the populations of only a few nematode groups (namely Aporcelaimellus, Dorylaimidae, Iotonchus, and Mononchus) with high colonizer-persister values. Although the reason for the higher abundance of specific nematode groups recorded during the winter is not explicitly clear, it is possibly linked to reduced competition from other soil fauna. This study clearly shows that further investigations are required to better understand the dynamics of grassland ecosystems.