Mixed Forest of Larix principis-rupprechtii and Betula platyphylla Modulating Soil Fauna Diversity and Improving Faunal Effect on Litter Decomposition

This research performed a comparison study to investigate how mixed forest affects the abundance, groups, and diversity of soil fauna and the effects of soil fauna on litter decomposition. We comparatively studied two forests, Larix principis-rupprechtii forest (LF) and mixed Larix principis-rupprechtii and Betula platyphylla forest (MF), which hold 30 years of stand age and are the representative forests in the mountainous area of northwestern Hebei, China. The field experiments were conducted from May to November 2020, with soil fauna and litter samples taken every one and a half months. A total of 540 soil samples (replicated samples, 3) were collected in each forest and the soil faunas were extracted from the samples by Tullgren methods in laboratory. Litter samples were incubated separately in the sampled forests using litterbags with two mesh sizes (0.01 and 4 mm) to observe the decomposition rate. In total, 2958 (inds.) soil faunas belonging to 4 phyla, 11 classes, and 20 orders, were found, with Acarina (1079/2958; 36.48%) and Collembola (1080/2958; 36.51%) being the dominant groups. The total abundance of soil fauna in the MF (1581 inds.) was higher than that in the LF (1377 inds.), and the significantly more abundant predatory functional group in the MF (p < 0.05) may indicate a more complex soil fauna food web structure. Comparatively, the higher Shannon–Wiener index (1.42–1.74) and Pielou evenness index (0.58–0.71) and the lower Simpson dominance index (0.22–0.32) in the MF suggested that the MF promoted the soil fauna diversity. The cumulative litter decomposition rate of litterbags with 4 mm aperture in the MF (54.52% in 300 days) was higher than that in the LF (32.81% in 300 days). Moreover, the litter decomposition rate was positively correlated with the total abundance and the number of groups, and was negatively with the Simpson dominance index, implying that the soil fauna activity effectively improved litter decomposition in the MF. Via the comparison, we found that the mixture of plant species in the forest can modulate the soil fauna diversity and accelerate the litter decomposition. The results in this study may provide an interesting reference for forest restoration and sustainable management.