Structural characteristics of soil fauna community
A total of 49 orders were included in the final dataset, including 14
classes in 4 phyla. We classified all sites into three climate types
based on their geographic locations, thermal characteristics, and water
availability, as follows: temperate, subtropical, and tropical. The
vegetation types include temperate coniferous and broad-leaved mixed
forest, temperate deciduous broad-leaved forest, subtropical evergreen
broad-leaved forest, and tropical rain forest (Figure 1). In general,
the number of orders declined significantly with increasing latitude of
overall orders, phytophage, and predacity faunas (Figure 1). The soil
fauna diversity in the temperate zone was significantly different from
that in the other two climatic zones
(ꭓ2 = 7.582,p = 0.02, Figure 1). The difference of phytophage
(ꭓ2 = 0.352, p = 0.839, Figure 1) and predacity
(ꭓ2 = 1.040, p = 0.595, Figure 1) orders were
not significant in the three climatic regions (Figure S1). Among the 14
sites being studied, the Jianfengling site belonged to the tropical rain
forest, showed the highest among all plots (Overall: 33, phytophage: 9,
predacity: 7). In contrast, the Aershan site, which belonged to the
coniferous and broad-leaved mixed forests in cold temperate zones,
showed the lowest species diversity among all plots (Overall: 14,
phytophage: 3, predacity: 3; Figure 1).
DCA analysis was conducted to show plot ordinations (Figure 2). The
highest similarity in order compositions was observed between Aershan
and Changbaishan. Further, Sapporo and Tahe were observed with similar
order compositions with Aershan and Changbaishan, as all of these four
sites were in high-latitude temperate regions. Analogously, high
similarities in order compositions were observed among the Tiantongshan,
Badagongshan, Xishuangbanna, and Jianfengling sites, which were all
located in low-latitudes subtropical and tropical regions.
The Monte Carlo permutation test showed that the total effects of
Latitude, MAT, MTCM, EMT, and SOC reached a significant level on overall
orders, phytophage, and predacity soil fauna composition (Table 4). The
results of RDA ordination showed that seven variables of spatial and
environmental factors can explain 31.7%, 36.0%, and 42.4% variation
of total information of soil animal composition at overall orders,
phytophage, and predacity, respectively (Figure 3).Specifically, the
1st ordination axis explains 18.7%, 20.9%, and 26.4% variation
information of overall orders, phytophage, and predacity, respectively,
and the 2nd ordination axis explains 13%, 15.1%, and 16% variation
information, respectively. Soil fauna community was observed to be
strongly affected by spatial and environmental factors (Table 4).
Community composition differed significantly in the different latitudes
(R2 = 0.519, p = 0.023). Variations in
fauna orders showed a strong response to soil physicochemical properties
(p = 0.004, Figure 3a) and temperature (p = 0.033, Figure
3a). The dominant Lumbricida belonging to Oligochaeta exhibited a
positive relationship with SOC or latitude but a negative relationship
with SBD, MAP, MAT, MTCM, or EMT
values (Figure 3a). However, for Malacostraca, the dominant Isopoda
showed a negative relationship with SOC or Latitude, but a positive
relationship with MAT, MTCM, or EMT (Figure 3a). The phytophage
Mesogastropoda belonging to Gastropoda was positively correlated with
SOC and negatively correlated with SBD (Figure 3b), whereas the
predacity Isoptera belonging to Insecta was observed as the opposite
(Figure 3c).