Naphthalene Addition Causes Slight Non-Target Effects on Soil Respiration and Soil Microbial Biomass in the Subalpine Forest of Western Sichuan

Naphthalene addition is a common method used to explore the functional roles of soil fauna, but its non-target effects on microcosms and field experiments have long been suspected. Here, we conducted a two-year-long in situ experiment with monthly naphthalene addition (100 g/m2 month) to assess the potential non-target effects of naphthalene addition on the soil respiration rate and soil microbial properties in the subalpine forest in western Sichuan. We found that the soil respiration rate ranged from 0.56 to 7.43 μmol/m2 s, exhibiting a typical monthly dynamic pattern characterized by a unimodal curve, that peaked in August. Naphthalene addition decreased the soil respiration rate in July and August and decreased the soil microbial biomass carbon to nitrogen ratio (MBC/MBN) and the MBC. However, naphthalene addition had no significant effects on such contents of soil as dissolved organic carbon (DOC) and nitrogen (DON), soil ammonia and nitrogen ( $${\text{NH}}_{4}^{ + }$$ -N), nitrate nitrogen ( $${\text{NO}}_{3}^{ - }$$ -N), soil MBN, or soil MBN, or the abundance of soil microbial PLFAs. These results suggest that the use of naphthalene to repel soil fauna has slight non-target effects on the soil respiration rate and soil microbial biomass and that these non-target effects should be tested before using naphthalene to explore the functional roles of soil fauna in field experiments in subalpine forests.