Diversity and Spatial-Temporal Distribution of Soil Macrofauna Communities Along Elevation in the Changbai Mountain, China

Biodiversity in mountain soils above the treeline

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

The joint effects of local, climatic, and spatial variables determine soil oribatid mite community assembly along a temperate forest elevational gradient

Numerous factors influence mountain biodiversity variation across elevational gradients and recognizing the relative importance is vital for understanding species distribution mechanisms. We examined oribatid mites at nine elevations (from 600 to 2200 m a.s.l) and four vegetation types from mixed coniferous and broad-leaved forests to alpine tundra on Changbai Mountain. We assessed the contribution of environmental factors (climatic and local factors) and spatial processes (geographic or elevation distances) to oribatid mite community assembly and identified 59 oribatid mite species from 38 families and 51 genera. With increasing elevation, species richness and the Shannon index declined significantly, whereas abundance followed a hump-shaped trend. Soil TP, NH4 +-N, MAT, MAP, and elevation were the critical variables shaping oribatid mite communities based on random forest analysis. Moreover, environmental and spatial factors, and oribatid mite communities were significantly correlated based on Mantel and partial Mantel tests. Local characteristics (3.9%), climatic factors (1.9%), and spatial filtering (8.8%) played crucial roles in determining oribatid mite communities across nine elevational bands (based on variation partitioning analyses of abundance data). Within the same vegetation types, spatial processes had relatively little effects, with local characteristics the dominant drivers of oribatid mite community variation. Environmental and spatial filters together shape oribatid mite community assembly and their relative roles varied with elevation and vegetation type. These findings are crucial for the conservation, restoration, and management of Changbai mountain ecosystems in the context of climate change, along with the prediction of future vertical biotic gradient pattern evolution.

Effects of Environmental Factors on the Spatial Distribution Pattern and Diversity of Insect Communities along Altitude Gradients in Guandi Mountain, China

Understanding the distribution patterns and underlying maintenance mechanisms of insect species is a core issue in the field of insect ecology. However, research gaps remain regarding the environmental factors that determine the distribution of insect species along altitudinal gradients in Guandi Mountain, China. Here, we explored these determinants based on the distribution pattern and diversity of insect species from 1600 m to 2800 m in the Guandi Mountain, which covers all typical vegetation ecosystems in this area. Our results showed that the insect community showed certain differentiation characteristics with the altitude gradient. The results of RDA and correlation analysis also support the above speculation and indicate that soil physicochemical properties are closely related to the distribution and diversity of insect taxa orders along the altitude gradient. In addition, the soil temperature showed an obvious decreasing trend with increasing altitude, and temperature was also the most significant environmental factor affecting the insect community structure and diversity on the altitude gradient. These findings provide a reference for exploring the maintenance mechanisms affecting the structure, distribution pattern, and diversity of insect communities in mountain ecosystems, and the effects of global warming on insect communities.

Changes in soil faunal density and microbial community under altered litter input in forests and grasslands

Root and foliar litter inputs are the primary sources of carbon and nutrients for soil fauna and microorganisms, yet we still lack a quantitative assessment to evaluate the effects of root and foliar litter on various groups of soil organisms across terrestrial ecosystems. Here, we compiled 978 paired observations from 68 experimental sites to assess the directions and magnitudes of adding and removing foliar and root litter on the soil faunal density and microbial biomass that was evaluated by phospholipid fatty acids (PLFAs) across forests and grasslands worldwide. We found that litter addition had only a marginal effect on soil faunal density but significantly increased the soil total microbial-, fungal- and bacterial-PLFAs by 13%, 14%, and 10%, respectively, across ecosystems, suggesting that the soil microbial community is more sensitive to carbon source addition than soil fauna, particularly in soils with low carbon to nitrogen ratios. In contrast, removing litter significantly decreased the soil faunal density by 17% but had few effects on soil microorganisms. Compared with foliar litter, root litter input had a more positive effect on the development of soil fungal taxa. The effect of both litter addition and removal on soil faunal density and microbial biomass did not differ between humid and arid regions, but a greater influence was observed in grasslands than in forests for soil microbial community. Our results highlight that the increasing litter production under a global greening scenario would stimulate microbial activity in grasslands more than in forests, and this stimulation would be greater for soil microbes than soil fauna.

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.