## 4 Discussion
### Naphthalene's Effects on Soil Fungal Communities and Litter Decomposition  
The mechanisms by which naphthalene may affect soil fungal communities include the (1) direct addition of new organic carbon, (2) an indirectly elevated level of carbon  
Figure 4: Relative abundance of soil fungal communities at the **(a)** phylum and **(b)** class level under the control (CK) and naphthalene (TR) treatments in a poplar plantation in northern Jiangsu, China. Figure 5: Comparison of relative abundances of soil fungal communities under control (CK) and naphthalene (TR) treatments at the order level in a poplar plantation in northern Jiangsu, China (Welch’s \(t\)-test). * 0.01 \(<p\leq\) 0.05; **0.001 \(<p\leq\) 0.01.  
availability through reduced arthropod detritivores, (3) the direct inhibition of a fungal community, (4) an indirectly decreased level of predation by fungivores, and (5) the indirect alteration of substrates via the reduced production of arthropod feces and dead bodies [23; 39; 45]. In this study, microbial biomass carbon content and fungal diversity did not increase, suggesting that the improvement in carbon availability through mechanisms (1) and (2) did not benefit soil fungal community growth. Both Ascomycota and Basidiomycota, which are saprophytic or symbiotic [46; 47; 48], were the predominant phyla in the TR and CK soils. However, they differed in terms of relative abundance, with higher Ascomycota numbers and lower Basidiomycota numbers resulting from the TR treatment compared to that of the CK treatment (Figure 4a). It was reported that Basidiomycota, particularly the saprotrophic, cord-forming basidiomycetes, gradually replaced Ascomycota during the course of litter decomposition [49; 50]. As the most potent decomposers of cellulose, Basidiomycete fungi have often been demonstrated to be prominent decomposers during late stages of litter decomposition as their capacity to synthesize enzymes is required for the degradation of relative complex polymers [51; 52]. The activity of extracellular enzymes produced by Basidiomycetes, such as \(\beta\)-glucosidase, cellobiohydrolase, N-acetylglucosaminidase, acid phosphatase, and phosphodiesterase, was proven to be most frequently affected by soil fauna activity (e.g., grazing), which can directly influence carbon, nitrogen, and phosphorus cycling [52]. The observed high relative abundance of Ascomycota and low relative abundance of Basidiomycota resulting from the TR treatment were likely a result of the unimproved substrate quality due to the suppressed level of soil fauna abundance and the reduced degree of litter decomposition under the TR treatment. More specifically, on the order level, the abundance of soil-resident Thelephorales under the TR was significantly lower than that for the CK treatment, while Capnodiales presented the opposite outcome (Figure 5). Naphthalene application not only drives away soil arthropods but also reduces the amount of arthropod feces and the number of dead bodies, which can alter the carbon substrates (lower C:N ratios and higher dissolved organic carbon content) and thus induce fungal growth [53]. The decreased abundance of Thelephorales might have been due to both the direct inhibition of naphthalene and the lack of a suitable substrate for its growth. Thelephorales, belonging to Basidiomycota, constitutes one of the groups of ectomycorrhizal fungi (ECM) that plays a critical role in a number of key ecosystem functions, such as nutrient mobilization from soil organic matter, carbon cycling, and linkages between trees and soil through common mycorrhizal networks [54; 55; 56]. Similar results were found in a laboratory Petri plate study, wherein naphthalene reduced radial growth in eight out of nine Basidiomycete fungi [57], while another study concerning a secondary fir forest on the eastern Tibetan Plateau, China, showed different results, wherein naphthalene stimulated basidiomycete mycelia; this disparity might have been provoked by the vast environmental differences of the study sites [58].