Effects of terrestrial isopods on soil nutrients during litter decomposition

Soil fauna are important biological factors that affect litter decomposition and play an important role in the release of nutrients, such as carbon and nitrogen. This study focused on the role of soil fauna in litter decomposition. Field microcosm experiments were conducted to assess the influence of isopods (Porcellionidae and Armadillidiidae) on soil nutrients during the litter decomposition of Catalpa bungei (CL), Platanus acerifolia (PL), and Aesculus chinensis (AL). The litter mass loss and nutrients in different soil layers treated with various isopods were determined in three-month microcosm incubations. Results showed that the presence of isopods significantly increased (P < 0.05) the litter decomposition rates compared with the control treatment (CK). The average weight (2.56 g) and total weight ratio (85.47%) of the isopod-decomposed litter were much larger than those of the CK treatment (0.43 g and 14.31%, respectively). In the different litter types collected, CL showed the highest decomposition rate among the different isopod treatments. Isopods increased the contents of organic carbon (OC), total nitrogen (TN), total potassium (TP), Olsen phosphorus (OP), available potassium (AK), ammonia nitrogen (NH₄⁺–N), and nitrate nitrogen (NO₃––N) in the surface soil by 59.19%, 27.36%, 2.72%, 29.30%, 5.85%, 13.10%, and 14.60%, respectively, relative to CK. The profile distribution of soil nutrients and the soil quality index under different isopod treatments were significantly (P < 0.05) greater in the 0–1 cm soil layer than in the 1–2, 2–4, and 4–6 cm soil layers. Further analysis showed that this significance was affected by decomposition time, isopod species, soil depth, and the interactions of these factors. The findings demonstrate that the isopods could accelerate litter decomposition and improve soil nutrients. This work provides evidence demonstrating that soil fauna can improve surface soil quality by promoting litter decomposition.