The impact of fertilization intensity on soil nematode communities in a Tibetan Plateau grassland ecosystem

Tibetan Plateau grasslands embody an important ecosystem featuring vibrant biogeochemical cycles. Soil fauna, particularly nematodes, play an important role in maintaining the integrity, function, and homeostasis of such ecosystem. In the Tibetan Plateau, studies exploring the influence of frequent fertilization practices on nematode communities and subsequent repercussions impacting the entire ecosystem are scarce. To investigate the effect of long-term fertilization on nematode communities in the eastern Tibetan Plateau of China, we monitored such communities under fertilization treatments ranging from 0 to 120 g m−2 year−1. To gain broader insights into the dynamic interrelationships within the ecosystem, we also monitored plant communities and modeled their bidirectional relationships with soil nematodes. Our data show that with higher fertilization intensities, overall plant productivity increases. Such gains are accompanied by reduction in plant community richness and predominance of grasses on the expense of sedges, legumes, and forbs. Fertilization also impacted the abundance and species richness of nematode communities; this effect was manifest in a hump-shaped relationship with both abundance and species richness of nematode communities peaking at 60 g m−2 year−1. The relationship between nematode biodiversity and aboveground plant production also exhibited a predominantly hump-shaped trajectory. Our model suggests that soil acidity and the ratio of available nitrogen-to-available phosphorus had indirect, yet strong, effects on the nematode community abundance and species richness, indicating that the decline of nematode communities beyond a 60 g m−2 year−1 treatment could, at least in part, be attributed to unfavorable soil conditions. Our findings augment our understanding of the responses of soil fauna to nitrogen and phosphorus additions in alpine grasslands and provide scientific basis for future management of grassland fertilization.