Global patterns and environmental drivers of soil fungal nematode antagonists, with a focus on croplands

Plant-parasitic nematodes can be suppressed by antagonistic members of the local soil microbiome. Compared to bacterial antagonists, considerably more attention has been paid to nematode-suppressing fungi. However, little is known about their global distribution. As their biogeography matters from both a fundamental and an applied perspective, we set out to mine the GlobalFungi database. After filtering on sample type, biome relevance and sequencing depth, we retained approximately 28,000 samples from 484 studies. An overview of fungal nematode antagonists was generated, and subsequent analyses revealed that 82.6% of the soil samples comprised ≥1 nematode antagonist. Most of these antagonists are not obligatory nematode parasites; they switch between trophic lifestyles including saprotrophism. Antagonists are frequently found across most biomes; the detection probability was highest in croplands (88% of samples), woodlands (82%), and grasslands (76%). Most of the common nematode antagonists are present on all continents and across climate zones, underlining their ecological flexibility. With one exception, the most frequently detected antagonistic fungi belonged to the fungal order Hypocreales, whose members are known to parasitize insects and fungi as well. Analysis of the impact of temperature and precipitation on common antagonists in croplands revealed mostly non-linear responses. Among a selection of six soil properties, pH was the most informative predictor for antagonist relative abundance in croplands. Our analyses revealed that nematode antagonists are more common and widespread than often assumed, especially in agro-ecosystems. Exploration of this suppressive potential will depend on our ability to create local conditions that favour a nematophagous lifestyle.