Responses of intestinal fungal community of Entomobrya proxima (Collembola: Entomobryinae) to fertilizer application

Soil collembolans play a key role in maintaining soil health, with their intestinal fungal community contributing to host physiology through specialized metabolic functions. Despite their ecological importance, how fertilizers affect these fungal community remains unclear. This study investigated the response of the intestinal fungal community in Entomobrya proxima Folsom (E. proxima), a dominant collembolan species in North China farmlands, to organic and inorganic fertilizer application using high-throughput sequencing and qPCR technology. The treatments included control group (CG) with no fertilizer, three different rates organic fertilizer treatments at 1 % (Organic fertilizer treatment 1, O1), 6 % (Organic fertilizer treatment 2, O2) and 10 % (Organic fertilizer treatment 3, O3) and inorganic fertilizer treatments at 1 % (Inorganic fertilizer treatment 1, I1), 4 % (Inorganic fertilizer treatment 2, I2) and 6 % (Inorganic fertilizer treatment 3, I3). The results showed significant variations in intestinal fungal community abundance, with O1 and I3 showing markedly higher levels than CG. Fertilizer application generally reduced the Chao1 (used to characterize species richness) (except I2) and Shannon (used to characterize species diversity and evenness) indices of intestinal fungal community, though it had no notable effect on overall community structure. Ascomycota emerged as the dominant phylum within the fungal community. Organic fertilizer application specifically modified the relative abundance of Microascus and Gibberella, whereas inorganic fertilizer significantly affected Scopulariopsis proportion. Saprotrophy was identified as the primary trophic mode, though increasing inorganic fertilizer application led to a gradual rise in pathotroph-saprotroph-symbiotroph proportion. Functional analysis indicated that dung saprotrophs and undefined saprotrophs predominated, with organic fertilizer reducing animal pathogen abundance while inorganic fertilizer enhanced it proportionally with rates. The microfungus exhibited a clear growth advantage in terms of morphological characteristics. Community assembly was primarily governed by stochastic processes, with drift being the key driver. Compared to CG, dispersal limitation played a more significant role under O1 and I2, while homogeneous and heterogeneous selection became more influential under O2 and O3, respectively. Furthermore, the niche width observed under O1 was significantly broader than that of CG. These findings demonstrated that fertilizer types and rates significantly altered the abundance, diversity, composition, trophic mode, functions and assembly mechanism of intestinal fungal community of E. proxima. In addition, organic fertilizer induced more pronounced changes than inorganic fertilizer, which will highlight previously overlooked impacts of agricultural practices on soil fauna.