## 3 Soil Features as a Consequence of Reduced Fertilization
### Soil Diversity
#### 3.3.2 Mycobiome  
Fungi play a pivotal role in the decomposition of OM, nutrient cycling, and the establishment of symbiotic associations with plants. It is crucial to highlight that their function within the soil microbiota community is commensurate with that of soil bacteria [90; 97]. Ascomycota, Basidiomycota, Mortierellomycota, and Mucoromycota represent the dominant fungal groups present in soil ecosystems [90; 97; 98]. The EU-recommended 20% reduction in N fertilization did not adversely affect the abundance of Ascomycota, Basidiomycota, and Mucoromycota in soil samples obtained from maize cultivation, as evidenced by the findings of [PERSON] et al. [90]. Conversely, in this experiment, Mortierellomycota exhibited a markedly lower relative abundance compared to the results recorded under maximum N application. Notably, the highest abundance of this phylum was observed in soil subjected to a 40% reduction in N fertilization, suggesting that this microorganism may be particularly sensitive to N inputs. In this specific experiment, a decline in Mortierellomycota abundance was indeed noted as N levels increased.  
Despite fungi being less sensitive to chemical fertilizers in comparison to other microbial groups [99], N fertilization exerts a significant impact on arbuscular mycorrhizal fungi [AMF], particularly affecting their community structure and diversity. High N levels were associated with a marked decline in AMF richness and biomass, primarily through the suppression of hyphal growth and spore germination [100]. AMF, belonging to the phylum Glomeromycota, are pivotal to plant-soil interactions, enhancing nutrient uptake, especially for N and P, through extensive hyphal networks that increase the absorptive surface area of plant roots [101; 102]. These fungi also contribute to soil stability by promoting the aggregation of soil particles, thus improving water retention and structural integrity [101]. Long-term N deposition has been shown to significantly reduce AMF biomass, diversity, and spore abundance, with soil acidification induced by N inputs being a key driver of this decline [100; 103]. Studies by [PERSON] et al. [100] revealed that AMF richness declined more dramatically after 11 years of N fertilization compared to 6 years, highlighting the cumulative impact of prolonged N enrichment. This decline in AMF diversity was further linked to shifts in fungal community composition, such as a reduction in the abundance of Glomeraceae, which was accompanied by an increase in Diversisporaceae--a group known for producing more extensive hyphal networks and with better adaptation to acidic soils [100]. In the context of global change and intensified agricultural practices, understanding the response of soil fungal communities, particularly AMF, to N fertilization is critical for maintaining soil health and plant productivity. AMF plays a crucial role in mitigating abiotic stressors such as drought and soil pH fluctuations, thus serving as key contributors to ecosystem resilience under changing environmental conditions [101; 102].  
[PERSON] et al. [104] evidenced that the agricultural soil mycobiome composition was dependent on both the seasons and the agricultural practices. They also found that even a 1-year break in the monoculture in favor of an intercropping mixture improved soil properties, thus contributing to greater biodiversity [104]. _Mortierella_ was recommended as a potential indicator of sensitivity to long-term maize cultivation, whereas _Solicoccozyma_ and _Exophilata_ were proposed as indicators of resistance to long-term maize cultivation [104]. The impact of N fertilization on the soil mycobiome is an intriguing and vital topic, necessitating comprehensive, longitudinal research to fully understand its effects on fungal diversity and function. In light of increasing environmental stressors, it is important to prioritize maintaining soil stability.