2.1 Study sites
The experiment was conducted at a subtropical forest in Zijin Mountain between April 2018 and May 2019 (32°4′N, 118°51′E; Nanjing, Eastern China). The forest is mainly covered by Quercus variabilis andPinus massoniana (Lin et al., 2017), and the herb layer is dominated by Parthenocissus quinquefolia or graminoids, mainlyCarex spp. (Tian et al., 2018). Mean annual rainfall and air temperature of the subtropical monsoon climate is 1106 mm and 15.4 °C, respectively. The rainfall concentrated in summer (on average 163 mm per month between June and August) and low in winter (on average 50 mm per month between October to March). The bedrock is sandstone and shale, with a humus layer rich in organic matter and nutrients. For a more comprehensive understanding of the role of deposited compounds and earthworms in different forests, we selected a deciduous Q. variabilis forest and a coniferous P. massoniana forest for this study (This work was conducted in the two forests respectively and without the replicates of the deciduous or coniferous forest). The two forests were about 900 m away from each other and located at similar altitude (65 and 175 m, respectively). More details on site conditions are given in Table 1.