Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau

Qin, Jiafeng; Liu, Changhai; Ai, Ning; Zhou, Yongwei; Tuo, Xianghui; Nan, Zhengzheng; Shi, Jiahao; Yuan, Caixia

doi:10.3390/land11111958

Open AccessArticle

Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau

¹

College of Life Science, Yan’an University, Yan’an 716000, China

²

Shaanxi Key Laboratory of Chinese Jujube, Yan’an University, Yan’an 716000, China

^*

Authors to whom correspondence should be addressed.

Land 2022, 11(11), 1958; https://doi.org/10.3390/land11111958

Submission received: 19 September 2022 / Revised: 29 October 2022 / Accepted: 31 October 2022 / Published: 2 November 2022

(This article belongs to the Special Issue Biodiversity Investigation and Conservation in China: Current Status, Challenges, and Perspectives)

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Abstract

:

Niche theory is significant for understanding the function of community structure, interspecific relationships, and community dynamic succession. However, there are few studies on the soil animal niche in returning farmland to forest areas on the Loess Plateau, making it challenging to comprehend the utilization of soil animal resources, the stability of the local community, and the succession process in the areas. Therefore, this study collected soil animals in five typical vegetation types: Robinia pseudoacacia (R), Hippophae rhamnoides (H), Populus simonii (P), Pinus tabulaeformis (T), and Armeniaca sibirica x Hippophae rhamnoides (M), with abandoned grassland (G) used as a control group. Then, the number of soil animal taxa, individuals, diversity, and niche were sampled and examined in the study areas during the four seasons of spring, summer, autumn, and winter using the manual sorting method and the Tullgren method. The results revealed that 3872 soil animals from 3 Phyla, 8 Classes, 22 Orders, and 49 Families were captured in the study areas. The dominant groups of soil macrofauna were Diptera larvae, Julidae, and Formicidae, and the dominant groups of meso–micro soil fauna were Oribatida, Protospira, and Collembola juveniles. Soil animals have rich nutritional function groups, with the most saprophytic soil animal groups. The individual density and taxa number of soil animals in G were lower than other vegetation on the whole. H, M, and P had a higher Shannon–Winner index than the other vegetation. Seasonal changes had different effects on macro and meso–micro soil fauna. The diversity of soil macrofauna is higher in spring and summer, and that of meso–micro soil fauna is higher in autumn and winter. Oribatida, Diptera Larvae, and Formicidae had a large niche width in the main taxa of soil animals, with universal adaptability to the environment. Cicadellidae and Culicidae had narrow niche widths and were highly dependent on resources and the environment. There were 67 pairs of highly overlapped (O_ik > 0.8) taxa of soil animals and 56 pairs of moderately overlapped (0.6 < O_ik ≤ 0.8) taxa, accounting for 80.39% of the total number of taxa. Soil animals had high commonality in resource utilization, intense competition, and poor community stability. As a result, we can conclude that the soil animal community in the study areas was in the stage of succession.

Keywords:

soil animal; community structure; niche width; niche overlap; returning farmland to the forest

1. Introduction

The Grain for Green Project (GFGP) is a major forestry ecological project of the Chinese government aimed at protecting and improving the ecological environment. For a long time, the blind destruction and reclamation of vegetation has caused serious soil erosion and sandstorm damage in China [1]. Natural disasters such as drought frequently occur, seriously endangering the production and lives of the Chinese people, and threatening the ecological security of the country. Based on this, in 1999, the Chinese government began to implement the project of returning farmland to forest, which covered 1897 counties and districts across the country. At present, China has completed the conversion of over 333,000 km² of farmland to forests and grasslands, and the forest coverage rate in the project areas has increased significantly [2]. As a typical gully area on the Loess Plateau, Wuqi County suffers from serious soil erosion. In order to improve the local ecological environment, the original cultivated land was converted into forests, and it won the honorary title of “the first county in China to return farmland to forests” [3].

The term “niche” in ecological subjects refers to how an organism fits into communities and natural ecosystems, and how it quantitatively describes the interactions between different species and their surroundings [4]. Niche theory is now widely used to explain the competition and coexistence of species [5]. The study of community niche plays an essential role in explaining species diversity, ecosystem stability, and community succession [6]. Currently, the majority of the research materials on niche are based on plant communities [7,8,9], with a small part on animal communities, which focuses primarily on zooplankton [10], fish [11], benthos [12], birds [13], and mammals [14,15], while there is even less pertinent research on soil animal communities [16,17,18].

The primary element of the soil ecosystem is its soil animals, which can participate in litter decomposition and nutrient cycling [19]. They have been utilized as the primary indicators for evaluating the environmental quality of soil due to their great sensitivity to environmental changes [20]. Wuqi County is a typical hilly and gully region of the Loess Plateau with a delicate ecological environment. It is situated to the north of Yan’an City in Shaanxi Province. On the basis of the long-term, effective and economic characteristics of vegetation restoration on the damaged ecological barrier [21], the state vigorously pursues the policy of returning farmland to the forest (grass). The forest and grass coverage and soil environment in Wuqi County have changed due to more than 20 years of forestry ecological engineering construction [22,23,24]. At present, the research on soil animals in Wuqi County mainly focuses on the impact of various vegetation types, site conditions, and soil physical and chemical properties on the composition and diversity of soil animal communities [25,26,27,28]. However, the research on the niche of soil animal communities is rare, which will impede people’s understanding of the utilization of soil animal resources and community relations in this area.

Based on this, this study utilized six typical vegetation types in the Jinfoping small watershed of Wuqi County as the research object, examined the characteristics of soil animal communities in different seasons, and applied niche theory to analyze the niche width and overlap of soil animals in these types. The following two issues must be resolved as a priority: (1) How does the vegetation type affect the soil animal community structure in Wuqi County? (2) How do the main taxa of soil animals differ regarding niche width and niche overlap? The purpose of this study is to obtain a deeper understanding of the community structure and distribution characteristics of soil animals in the Jinfoping watershed, as well as the adaptability of soil animals to the environment and their competitiveness with resources. In this way, we can provide essential data for the management of soil biodiversity and ecosystem resources in the study area, as well as theoretical backing for the evaluation of soil ecosystem stability and the rational construction of vegetation in returning farmland to forest areas of the Loess Plateau.

2. Materials and Methods

2.1. Overview of the Study Area

The study area is located at an altitude of 1500 to 1600 m in the Jinfoping small watershed (108°12′09″–108°23′20″ E, 36°21′09″–37°21′20″ N) in Wuqi County, Yan’an City, Shaanxi Province. It is characterized by a semi-arid temperate continental monsoon climate. The annual average temperature is 7.8 °C, the annual average frost-free period is 130 days, and the annual average rainfall is 395.4 mm, most falling between July and September. The landform is part of the Loess Plateau’s girder-shaped hilly and gully region, and the soil is mostly loess. The vegetation in this area consists primarily of Robinia pseudoacacia (L.), Populus simonii (Carr.), Pinus tabulaeformis(Carr.), Armeniaca sibirica (L.) × Hippophae rhamnoides (L.) and other trees, as well as Hippophae rhamnoide(L.) and other shrubs, Potentilla chinensis (Ser.), Lespedeza cuneata (Dum.-Cours.), Rubia cordifolia (L.) and other herbaceous vegetation. Table 1 contains detailed information about the sample plot.

2.2. Collection of Soil Fauna

Six typical vegetation types were selected in the study area in the middle of April, July, October, and December 2020. The vegetation in this study was a typical afforestation tree species widely planted in the process of returning farmland to forest. Grassland was naturally formed and developed after farmland was abandoned. Fixed plots of 20 m × 20 m were laid out in each vegetation distribution area. Three 5 m × 5 m sample points were set in each sample as a repeat, and 3 sample squares were set in each sample point. The manual sorting method and the Tullgren method were used to collect and separate soil animals, which are common to international standards [29]. Soil macrofauna were sampled by the manual sorting method, with a sampling area of 25 cm × 25 cm and a depth of 15 cm, and each soil sample was carefully examined the soil surface litter and blocks, and picked soil animals with a body width greater than 2 mm from inside, which took about 20 min. It was fixed in a 75% alcohol bottle, labeled, and brought back to the laboratory for identification. collected soil meso- and microfauna using a soil stainless steel ring (diameter 5 cm, height 5 cm) and soil samples with an area of 10 cm × 10 cm and a sampling depth of 15 cm, and brought them back to the laboratory. Then, they extracted them using the Tullgren, separated them under a 60 W incandescent lamp for 48 h, and stored the isolated soil animals in a 75% alcohol solution and labeled them. We spent about 5 days collecting them in each sample.

2.3. Identification of Soil Fauna

According to the “Pictorial Keys to Soil Faunas of China [30]”, the collected soil animals were categorized and identified, and the number of taxa and individuals at each sampling point was counted. The adult and Larvae were counted separately, considering they have diverse functions at different developmental stages (Coleoptera, Diptera, and Lepidoptera, etc.).

2.4. Statistical Analysis

The number of taxa, individual density, diversity index, and other data related to soil animals was compiled and analyzed using Excel 2019; one-way analysis of variance (ANOVA) was used to compare the differences in the individual number, taxa number, and the community diversity index of soil animals throughout four seasons; the niche width index of Levins (B_i) [31] and niche overlap value of Pinaka (O_ik) [32] of the primary soil animal taxa were calculated by R.4.1.3 (spaa package). The Origin 2018 software was used to map the individual number, taxa number, and diversity index of soil animals. The cluster heat map of niche overlap values was drawn using R.4.1.3 (pheatmap package).

Formulas (1–4) can be used to calculate the diversity, and niche index of soil animals:

H = - \sum \frac{n_{i}}{N} \cdot \ln (\frac{n_{i}}{N})

(1)

M = (S - 1) / \ln N

(2)

B_{i} = \frac{1}{\sum_{j = 1}^{r} p_{i j}^{2}}

(3)

O_{i k} = \frac{\sum_{j = 1}^{r} (P_{i j} \cdot P_{k j})}{\sqrt{j = \sum_{j = 1}^{r} P_{i j}^{2} \sum_{j = 1}^{r} P_{i k}^{2}}}

(4)

where, H: Shannon–Wiener index, M: Margalef index.

“ n_{i} ”

represents the number of individuals in the

i

th taxa; “N” represents the total number of individuals;

“ i ”

represents the number of taxa;

P_{i j}

represents the proportion of the individual number of the

i

th taxa in resource “j” to the total number of individuals of the taxa under each resource state (

P_{i j} = n_{i j} / N_{i}

).

” r ”

is the number of samples.

P_{i k} = n_{i k} / N_{i}

, where

“ k ”

is another soil animal taxa different from

“ i ”

, with the value of

O_{i k}

ranging from 0 to 1. Highly overlapping: O_ik > 0.8; moderate overlapping:0.6 < O_ik ≤ 0.8; low overlapping: O_ik ≤0.6.

3. Results

3.1. Community Structure of Soil Animals

3.1.1. Composition of Soil Animal Community

A total of 3872 soil fauna were captured in April, July, October, and December 2020, belonging to 3 Phyla, 8 Classes, 22 Orders, and 49 Families (Table 2, see Appendix A for the full taxa list), of which 56 classes of soil macrofauna, the dominant taxa were Diptera Larvae, Julidae, and Formicidae. The common taxa include Coleoptera Larvae, Gnapphosidae, Lepidoptera Larvae, Pyrrhocoridae, Culicidae, Staphylinidae, Hemiptera Larvae, Cicadellidae, Carabidae, Curculionidae, Thomisidae, and Aphidoidea, accounting for 84.29% of the total number of soil macrofauna, the remainder was rare; there were eight classes of meso–micro soil fauna, and the dominant taxa were Oribatida, Prostigmata, and Collembola juveniles. The common groups include Entomobryidae, Rhabditida, and Thripidae. The rare taxa account for 1.11% of the total number of meso–micro soil fauna. The soil animal taxa in the study area include a wide range of nutritional functional taxa, with saprophagous ones accounting for the highest (76.66%), followed by omnivorous (17.3%), while predatory accounts for the lowest (0.82%) (Table 2).

In terms of the distribution of soil animals, except for the Hemiptera Larvae, the Pyrrhocoridae and the Aphidoidea, the other dominant taxa and common taxa were distributed in more than four vegetation types, so it can be considered that these dominant groups and common taxa were the main groups of soil animals in the areas where farmland was returned to forest and play an important role in the forest ecosystem.

3.1.2. Diversity of Soil Animals

In spring, the density of soil macrofauna in G was the lowest, the M was the highest, the density of meso–micro soil fauna in H was the highest, and the G was the lowest. In summer, the density of soil macrofauna and the density of meso–micro soil fauna of P were the highest. In autumn, the density of soil macrofauna in M was significantly higher than that of P and T (p < 0.05), and the density of meso–micro soil fauna in P and T was significantly lower than that of other vegetation (p < 0.05). In winter, the density of soil macrofauna in G was lower than that of other vegetation, and the density of meso–micro soil fauna in P and G was lower than that of other vegetation. In spring, except for Robinia acacia, the taxa of soil macrofauna of other vegetation were higher than those in G, and the taxa of meso–micro soil fauna of other vegetation except P was significantly higher than that of G (p < 0.05). In summer, there was little difference in the taxa of soil macrofauna among vegetation, and the number of small soil fauna in G was lower than that of other vegetation; In autumn, the number of soil macrofauna in G was the highest, and the difference between meso–micro soil fauna was not large. In winter, the taxa of soil macrofauna and meso–micro soil fauna in G were lower than those of other vegetation (Figure 1 and Figure 2). In general, the individual density and taxa of macro, meso–micro soil fauna in G were lower than those in plantations.

The seasonal dynamics of the density and taxa of soil macrofauna in each vegetation type were as follows: the seasonal dynamics of the density of soil macrofauna in P was not obvious, while the seasonal dynamics of the density of soil macrofauna in other vegetation type were significant (p < 0.05), and the lowest in winter (Figure 1A). There were significant differences in the number of soil macrofauna taxa for each vegetation type (p < 0.05). The number of soil macrofauna taxa of R, H and M was the highest in summer, that of P and T were higher in spring, and that of G was the highest in autumn (Figure 1B). It can be seen from the above seasonal dynamics that the seasonal dynamics of the density of soil macrofauna taxa of P was not obvious, and there were significant differences in the density and number of soil macrofauna taxa of other vegetation. Among them, the seasonal changes of the density and number of soil macrofauna taxa of R, H and M were consistent. The seasonal dynamics of the density and number of soil macrofauna taxa in G were basically consistent, with the highest in autumn, no significant difference between spring and summer, and the lowest in winter.

The seasonal dynamics of the density and number of taxa of meso–micro soil fauna in each vegetation type were as follows: the seasonal dynamics of the density of Meso–micro soil fauna in each vegetation type were significant (p < 0.05), and the lowest in winter. Among them, the seasonal change trend of soil animal density of R, H, and M was the same, showing a higher density in spring and autumn, and a lower density in winter and summer. The change trend of the density of T and G was basically the same, showing a significantly higher state in autumn and winter than in spring and summer (Figure 2A). The seasonal dynamics of the number of small and meso–micro soil fauna taxa in various vegetation types were also significant (p < 0.05). The number of R was significantly higher in winter than in spring and summer (p < 0.05); H was significantly higher in winter than in spring, summer, and autumn (p < 0.05); P was significantly higher in autumn than in spring and summer (p < 0.05); M and H were higher in autumn and winter than in spring and summer (p < 0.05); and the number of soil animal groups of P and G were significantly higher in autumn and winter than in spring and summer (p < 0.05) (Figure 2B). In general, the density and number of meso–micro soil fauna taxa in different vegetation types were significantly different. The density and number of taxa of G and T soil animals in autumn and winter were significantly higher than those in spring and summer.

In the same season, the Shannon index and Margalef’s index of macro and meso–micro soil fauna in different vegetation were as follows: in spring, the Shannon index of soil macrofauna in the M and P were higher, and the Shannon index of meso–micro soil fauna in the M was significantly higher than that of T and G (p < 0.05); in summer, the Shannon index of soil macrofauna in M and R were higher, that of T was the smallest, that of meso–micro soil fauna in R and P were higher, and that of T was the smallest; in autumn, the Shannon index of macro soil animals of R was the highest, and the meso–micro soil fauna of P and H were higher; in winter, the Shannon index of soil macrofauna of H and R were higher, while that of G was the lowest. The Shannon index of meso–micro soil fauna of H and M were higher, and that of T was the lowest. The Shannon index and Margalef’s index of macro, meso–micro soil fauna were basically the same (Figure 3 and Figure 4). In general, the Shannon index and Margalef’s index of M, R, and P were higher, while those of T and G were lower.

The seasonal dynamics of the soil macrofauna Shannon index of each vegetation type were significant (p < 0.05). Among them, the Shannon index of R macrofauna in summer and autumn was significantly higher than that in spring and winter; the diversity of H in summer was significantly greater than that in winter; the diversity of P in spring and summer was significantly higher than that in autumn and winter; the M in summer was significantly higher than that in spring, autumn and winter; the Shannon index of T and G in spring, summer and autumn was significantly higher than that in winter (Figure 3A). The seasonal changes of Margalef’s index and Shannon index of soil macrofauna of various vegetation types were basically consistent (Figure 3B). In general, the Shannon index and Margalef’s index of macrofauna in spring and summer were significantly higher than in autumn and winter.

The seasonal dynamics of the Shannon index and Margalef’s index of meso–micro soil fauna in different vegetation types were significant (p < 0.05). Among them, the seasonal variation trend of the Shannon index of meso–micro soil fauna in the R and M was consistent, and both autumn and winter were higher than spring and summer; the Shannon index of H was significantly higher in winter than in summer; P in autumn was significantly higher than that in summer; the G in autumn and winter was significantly higher than that in spring and summer (Figure 4A). Seasonal changes of Margalef’s index and the Shannon index of meso–micro soil fauna in different vegetation types were basically one (Figure 4B). On the whole, the Shannon index and Margalef’s index of meso–micro soil fauna in autumn and winter were significantly higher than those in spring and summer.

3.2. Main Soil Animal Niche

3.2.1. Niche Width of Main Soil Fauna

Calculations of the soil fauna niche widths of the six vegetation types in the study area revealed seasonal differences in the niche widths of soil fauna taxa (Table 3). The Formicidae and Diptera Larvae have the largest ecological niche width in spring, with niche indices of 4.30 and 4.31, respectively; the Cicadellidae (1.0) and Curculionidae (1.0) have the smallest. In summer, the Formicidae, Gnaphosidae, Coleoptera Larvae, and Oribatida have larger ecological niche widths, with ecological niche indices of 4.90, 4.81, 4.67, and 4.40, and the Collembola juveniles and Thripidae have smaller ones, with ecological niche indexes of 1.80 and 1.83. In autumn, the Oribatida, Prostigmata, Collembola juveniles, Formicidae, Diptera Larvae, and Julidae have larger niche widths, with niche indices of 5.55, 5.40, 5.38, 4.88, 4.76, and 4.28, respectively, and the Staphylinidae (1.0) and Cicadellidae (1.0) have smaller ones, with niche indices of 1.00 and 1.80, respectively. In winter, the Collembola juveniles and Diptera Larvae have larger niche widths, with niche indices of 4.54 and 4.13, while the Gnaphosidae, Cicadellidae, Curculionidae, and Thomisidae have smaller ones, with niche indexes of 1.00 and 1.98, respectively. The top three in niche width were Oribatida, Diptera Larvae, and Formicidae.

3.2.2. Niche Overlap Values of Major Soil Fauna

Among the different vegetation types in the four seasons, the distribution range of the main soil fauna taxa niche overlap (O_ik) was [0, 1], and there were 67 pairs of highly overlapping taxa (O_ik > 0.8), 56 pairs of moderate overlapping taxa (0.6 < O_ik ≤ 0.8), and 30 pairs of low overlapping (0.6 ≤ O_ik), accounting for 43.79%, 36.60%, and 19.61% of the total logarithm, respectively. Among them, the Oribatida has the highest overlap with the Collembola juveniles and the Prostigmata, with an overlap value of 0.98; the taxa pairs with the lowest overlap values were the Rhabditida and the Lepidoptera Larvae, with an overlap value of 0.31 (Figure 5). Overall, the ecological niches of soil fauna communities in the study area overlapped greatly, and there was a significant ecological similarity between the main taxa. In addition, there was high utilization degree of the same kinds of resources, fierce competition, and poor community stability, with the soil fauna in the study area in the succession stage.

4. Discussion

Composition and Structure of Soil Animal Community

Numerous studies have demonstrated the strong relationship between soil animals and vegetation types. Different vegetation can directly or indirectly influence the characteristics of soil animal communities by altering the understory microenvironment, soil microbial community composition, and soil physical and chemical properties [34,35,36]. The dominant groups of soil macrofauna in the reforestation area of Jinfoping small watershed are Diptera Larvae, Julidae, and Formicidae, and the common groups are Coleoptera Larvae, Gnaphosidae, Lepidoptera Larvae, Pyrrhocoridae, Culicidae, Staphylinidae, etc., accounting for 84.29% of the total number of soil macrofauna. The dominant groups of meso–micro soil fauna are the Oribatida, Prostigmata, and Collembola juveniles, and the common groups include the Entomobryidae, Rhabditida, and Thripidae. They constitute the majority of soil animals in the study area and play an important role in the forest soil ecosystem. Similar research findings have been found by Yang Lihong [37], Li Xiaohan et al. [38], Yang Di et al. [39], and Li Tao et al. [40]. However, some discrepancies may be due to variations in the quality and quantity of litter, root exudates, soil microorganisms and their metabolites in different areas [41].

The structure of soil food webs governs the processes and functions of ecosystems [42,43]. The proportion of trophic functional taxa among soil animals in this study was in the following order: Saprophytic soil animals > omnivorous soil animals > bacterial soil animals > phytophagous soil animals > predatory soil animals. This is consistent with the research results of Dong Yuliang et al. [44]. Oribatida and Prostigmata feed on the residues of soil surface animals and plants and provide nutrition and energy for underground soil animals of various trophic levels. It is generally believed that there is a positive correlation between saprophytic soil animals and soil fertility [45]. It can be seen from Table 2 that the density of saprophytic soil animals in the vegetation of Plantations in the study area is significantly higher than that of G, which to some extent indicates that the measures of returning farmland to forests have promoted the improvement of regional soil fertility. In addition, as primary consumers, the individual density of phytophagous soil animals is too low, which may have a negative impact on the food chain of soil animals.

Vegetation type is an important factor affecting the change in the soil animal community. In different seasons of the study area, the characteristics of soil animal communities are different among different vegetation, which is similar to the research results of Han Huiying et al. [46]. According to the four seasons, the vegetation with the higher density, group number and diversity of large soil animals is the M and P, which may be because mixed forests can make full use of resources such as light and water at different times, with high stability of forest stand and rich understory vegetation, which can provide richer space and food sources for soil fauna [47]. P is a deciduous broad-leaved forest, and its litter is easily decomposed into organic matter, which is conducive to the survival and reproduction of soil animals [48]. The vegetation types with high density, taxa number and diversity of meso–micro soil fauna are H and P. Because H has developed roots and rhizobia, it can rapidly increase the content of soil organic matter and nitrogen in a short time [49], providing nutrition and space for meso–micro soil fauna in deep soil. Overall, the soil fauna density and taxa of P and G are lower than those of other vegetation, which may be related to the lower litter content of G and the allelopathic effects of T [50]. Another important factor influencing soil animals is the season. The diversity of soil macrofauna in the study area is higher in spring and summer. Some studies show that there is a significant positive correlation between soil macrofauna and temperature [51]. The Loess region in northern Shaanxi belongs to a typical temperate continental monsoon climate. With the rise of temperature in spring, large soil animals recover, and the reproduction of large soil animals reaches a peak in the summer high-temperature period. In contrast to large soil animals, the diversity of meso–micro soil fauna is higher in autumn and winter. However, in summer when rainfall is high, the diversity is low, which may be due to the weak migration capacity of meso–micro soil fauna, and the over saturation of soil water in summer leads to the anoxic death of some soil animals [52], the low rainfall and rising temperature in spring are also reasons for the low diversity. Soil moisture in autumn and winter may be more suitable for the survival of small and medium-sized soil animals.

Niche width can be used to measure a species’ resource utilization scope, environmental adaptability and its position and function in the community [53,54], The soil fauna in the Jinfoping watershed has a large ecological niche in the springtime that is occupied by Diptera Larvae and Formicidae, which are widely dispersed in six samples and exhibit universal environmental adaptability. With a narrow distribution range, the Cicadellidae and Curculionidae have a smaller ecological niche width, which is more selective and depends more on their surroundings for resources. The Formicidae, Gnapphosidae, Coleoptera Larvae, and Oribatida have larger ecological niche widths in summer; the Oribatida, Prostigmata, Collembola juveniles, Formicidae, Diptera Larvae and Julidae in autumn; and the Collembola juveniles and Diptera Larvae in winter. Additionally, the range of resources available to soil animals changes with time, which impacts the niche width of both different soil animals and the same soil animal [55]. The Oribatida, Diptera Larvae, and Formicidae have the largest ecological niche width over four seasons, indicating that these three taxa play a vital role in the soil fauna community in the area of returning farmland to the forest in the Jinfoping watershed and can fully utilize the ecological resources of the area, with a wide range of ecological adaptation and generalist species. The Culicidae, Cicadellidae, and Thomisidae had smaller niche widths. The fierce competition for resources among species and the propensity for habitat specialization had certain significance as indicator species of soil through the same taxon’s characteristics of changing ecological niche width under different trophic states [56].

Ecological niche overlap values represent the degree of cross and overlap in resource utilization between different biological taxa [57]. In the Jinfoping watershed, there are 67 pairs of taxa with high overlap (O_ik > 0.8), and 56 pairs of moderate overlap (0.6 < O_ik ≤ 0.8), accounting for 80.39% of the total taxon logarithm. It demonstrates the high overlap values between the dominant taxa in the study area, the similarity in resource demands between species, the relative similarity in degrees of environmental adaptation, and the competition interference, which actively prevents their peers from accessing the necessary resources and maintains their unique resource requirements [58]. Among the pairs of species, the Oribatida had the highest overlap with the Collembola juveniles and Prostigmata (O_ik = 0.98), indicating that there is intense competition between species and that the two taxa have a high degree of similarity in terms of resource utilization. The Rhabditida and Lepidoptera Larvae had the smallest niche overlap values (O_ik = 0.38), indicating that the two had more distinct environmental and resource preferences and lower levels of interspecific competition. In conclusion, the soil fauna community in the study area is currently in a succession stage based on the high overall ecological niche overlap of soil fauna, the high commonality of species utilization of resources, fierce competition, and low stability of the main soil fauna community in the Jinfoping basin.

5. Conclusions

This paper investigated the characteristics and ecological niches of soil fauna of different vegetation types in the Jinfoping Watershed in Wuqi County, and the following conclusions were reached:

(1) The soil fauna captured in the study area belonged to 3 Phyla, 7 Classes, 21 Orders, and 49 Families. The dominant groups of soil macrofauna are Diptera Larvae, Julida, and Formicidae, and the dominant groups of meso–micro soil fauna are Oribatida, Protospira, and Collembola juveniles. Soil animals have rich nutritional function groups, with the most saprophytic soil animal groups.

(2) The diversity of soil animals in H, M, and P is higher, and the individual density and taxa number of soil animals in G are lower than other vegetation on the whole. Seasonal changes have different effects on macro and meso–micro soil fauna. The diversity of soil macrofauna is higher in spring and summer, and that of meso–micro soil fauna is higher in autumn and winter.

(3) With large niche width, Oribatida, Diptera Larvae, and Formicidae demonstrated universality for the environment of six different reclaimed woodlands in the study area.

(4) In the Jinfoping watershed, there is a fair amount of overlap between soil fauna ecological niches, a high level of species commonality in terms of resource utilization, fierce competition state, and poor stability of soil fauna communities. The community is in the succession stage and is developing towards the top community.

Author Contributions

Conceptualization, C.L. and N.A.; methodology, C.L. and N.A.; software, J.Q.; validation, J.Q.; C.L. and N.A.; formal analysis, J.Q.; C.L. and N.A.; investigation, J.Q., Y.Z., X.T., Z.N., J.S., C.Y., C.L. and N.A.; resources, C.L. and N.A.; data curation, J.Q., Y.Z., X.T., Z.N., J.S., C.Y., C.L. and N.A.; writing—original draft preparation, J.Q.; writing—review and editing, J.Q.; C.L. and N.A.; visualization, J.Q.; C.L. and N.A.; supervision, C.L. and N.A.; project administration, C.L. and N.A.; funding acquisition, C.L. and N.A. All authors have read and agreed to the published version of the manuscript.

Funding

This study project was funded by the National Natural Science Foundation of China Project (32060297, 31370541) and the Natural Science Basic Research Program of Shaanxi Province (2021 JQ-626).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A. Full Taxa List of Soil Fauna

Phyla	Class	Order	Family
Arthropoda	Insecta	Coleoptera
			Elateridae
			Staphylinidae
			Chrysomelidae
			Scarabaeidae
			Carabidae
			Curculionidae
			Pselaphidae
			Coccinellidae
			Tenebrionidae
			Silphidae
			Lathridiidae
			Scydmaenidae
			Coleoptera Larvae
		Hymenoptera
			Chalcidoidea
			Formicidae
		Orthoptera
			Acridoidea
			Orthoptera Larvae
		Hemiptera
			Cicadellidae
			Aphidoidea
			Fulgoridae
			Cicadidea Larvae
			Lygaeidae
			Tingidae
			Cydnidae
			Reduviidae
			Pyrrhocoridae
			Pentatomidae
			Coreidae
			Hemiptera Larvae
		Diptera
			Diptera larva
			Culicidae
		Dermaptera
			Dermaptera larva
		Lepidoptera
			Lepidoptera larva
		Thysanoptera
			Thripidae
		Trichoptera
		Mantodea
			Mantidae
	Arachnoidea	Araneae	Araneidae
			Salticidae
			Gnaphosidae
			Linyphiidae
			Clubionidae
			Thomisidae
			Agelenidae
			Lycosidae
			Oxyopidae
			Zoridae
			Liocranidae
			Hahniidae
		Opiliones
			Phalangiidae
		Acariformes
			Oribatida
			Prostigmata
		Pseudoscorpiones
	Crustacea	Isopoda
			Oniscidae
	Diplopoda	Julida
			Julidae
	Chilopoda	Geophilomorpha
		Scolopendromorpha
		Lithomorpha
	Collembola	Collembola
			Isotomidae
			Entomobryidae
			Sminthuridae
			Collembola juveniles
Mollusca	Gastropoda	Stylommatophora
			Bradybaenidae
			Ariophantidae
			Carychiidae
Nemata	Secernentea	Rhabditida

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Figure 1. Density and number of groups of soil macrofauna in different vegetation. Note: (A,B) represent densities and group of numbers soil macrofauna, respectively. Capital letters represent the differences between different vegetation in the same season, and lowercase letters represent the differences between different seasons of the same vegetation. Different letters in the figure show significant difference (p < 0.05), the same below.

Figure 2. Density and number of groups of meso–micro soil fauna in different vegetation. Note: (A,B) represent densities and group of numbers meso–micro soil fauna, respectively. Capital letters represent the differences between different vegetation in the same season, and lowercase letters represent the differences between different seasons of the same vegetation. Different letters in the figure show significant difference (p < 0.05), the same below.

Figure 3. The Shannon index and Margalef’s index of soil macrofauna in different vegetation. Note: (A,B) represent the Shannon index and Margalef’s index for soil macrofauna, respectively. Capital letters represent the differences between different vegetation in the same season, and lowercase letters represent the differences between different seasons of the same vegetation. Different letters in the figure show significant difference (p < 0.05), the same below.

Figure 4. Shannon index and Margalef’s index of meso–micro soil fauna in different vegetation. Note: (A,B) represent the Shannon index and Margalef’s index for meso–micro soil fauna, respectively. Capital letters represent the differences between different vegetation in the same season, and lowercase letters represent the differences between different seasons of the same vegetation. Different letters in the figure show significant difference (p < 0.05), the same below.

Figure 5. Heat map of Niche overlap values of major soil fauna taxa. Note: The vertical and horizontal coordinates in the figure use the first four letters of the soil animal to represent different species.

Table 1. Basic conditions of sample plot.

Sample Plots	Age of Stand	Elevation	Aspect	Slope (Degree)	Latitude-Longitude	Soil pH	The Main Undergrowth Vegetation
Robinia pseudoacacia (R)	22	1449	Half shaded slope	21	108°17′37″ E, 36°55′01″ N	Alkalescence	Patrinia rupestris (Pall.), Rubia cordifolia (L.), Lespedeza cuneata (Dum. -Cours.)
Hippophae rhamnoide (H)	21	1430	shaded slope	25	108°09′37″ E, 36°50′52″ N	Alkalescence	Potentilla chinensis (Ser.), Glycyrrhiza pallidiflora (Maxim.),
Populus simonii (P)	22	1434	half shaded slope	20	108°12′31″ E, 36°45′50″ N	Alkalescence	Lespedezadavurica (Laxm.) Schindl., Cirsium japonicum (Fisch.), Potentilla chinensis (Ser.)
Pinus tabulaeformis (T)	18	1510	half shaded slope	28	108°13′10″ E, 36°53′33″ N	Alkalescence	Potentilla chinensis (Ser.), Cirsium lineare (Thunb.), Lespedeza cuneata (Dum. -Cours.)
Armeniaca sibirica xHippophae rhamnoides (M)	22	1430	half shaded slope	20	108°12′43″ E, 36°49′55″ N	Alkalescence	Hemistepta lyrata (Bunge.), Artemisia annua (L.), Saussurea japonica (Thunb.), Ampelopsis aconitifolia (Bge.)
Abandoned grasslan (G)	/	1400	shaded slope	27	108°12′29″ E, 36°49′55″ N	Alkalescence	Viola phillipina, Lespedeza cuneata (Dum.-Cours.), Cirsium lineare (Thunb.)

Table 2. Soil fauna community composition in the study area.

Species, Individuals/m²	R	H	P	T	M	G	Total	Abundance (%)	Function
Collembola	1833.33 (47.14)	3366.67 (309.12)	4100 (653.2)	3533.33 (478.42)	3900 (216.02)	1700 (141.42)	18,433.33	19.12	O
Isotomidae	33.33 (47.14)	366.67 (47.14)	—	66.67 (47.14)	233.33 (94.28)	—	700.00	0.73	F
Entomobryidae	266.67 (47.14)	466.67 (94.28)	900 (294.39)	133.33 (124.72)	1133.33 (94.28)	33.33 (47.14)	2933.33	3.04	F
Sminthuridae	166.67 (124.72)	66.67 (47.14)	33.33 (47.14)	100 (81.65)	—	—	366.67	0.38	Ph
Collembola juveniles	1366.67 (169.97)	2466.67 (385.86)	3166.67 (385.86)	3233.33 (612.83)	2533.33 (124.72)	1666.67 (169.97)	14,433.34	14.97	O
Acariformes	10,066.6 (471.4)	14,700 (1042.4)	16,000 (864.1)	13,400 (864.1)	9066.67 (286.74)	8266.67 (249.44)	71,500.01	74.14	S
Oribatida	4766.67 (47.14)	10,033.3 (679.87)	7933.33 (464.28)	8866.67 (543.65)	4533.33 (974.11)	4266.67 (235.7)	40,400.00	41.89	S
Prostigmata	5300 (496.66)	4666.67 (368.18)	8066.67 (492.16)	4533.33 (368.18)	4533.33 (784.57)	4000 (81.65)	31,100.00	32.25	S
Rhabditida	600	566.67 (124.72)	1266.67 (339.93)	233.33 (188.56)	1333.33 (402.77)	400 (163.3)	4400.00	4.56	S
Thysanoptera: Thripidae	133.33 (47.14)	433.33 (205.48)	1200 (81.65)	33.33 (47.14)	166.67 (94.28)	133.33 (124.72)	2099.99	2.18	O
Hemiptera	58.67 (19.96)	64 (22.63)	181.33 (114.14)	101.33 (79.82)	53.33 (27.19)	133.33 (19.96)	591.99	10.44	O
Cicadellidae	—	10.67 (15.08)	10.67 (7.54)	32 (13.06)	16 (13.06)	10.67 (7.54)	80.01	1.41	Ph
Aphidoidea	—	5.33 (7.54)	—	42.67 (60.34)	16 (22.63)	—	64.00	1.13	Ph
Fulgoridae	—	5.33 (7.54)	—	—	—	—	5.33	0.09	Ph
Cicadidea Larvae	—	16 (13.06)	21.33 (7.54)	10.67 (15.08)	5.33 (7.54)	—	53.33	0.94	Ph
Lygaeidae	10.67 (15.08)	10.67 (7.54)	5.33 (7.54)	—	—	—	26.67	0.47	Ph
Tingidae	5.33 (7.54)	—	—	5.33 (7.54)	—	—	10.66	0.19	Ph
Cydnidae	—	—	—	—	—	16 (13.06)	16.00	0.28	Ph
Reduviidae	5.33 (7.54)	10.67 (7.54)	—	—	5.33 (7.54)	—	21.33	0.38	Pr
Pyrrhocoridae	10.67 (15.08)	—	144 (94.21)	—	—	21.33 (7.54)	176.00	3.10	Ph
Pentatomidae	—	5.33 (7.54)	—	10.67 (15.08)	5.33 (7.54)	5.33 (7.54)	26.66	0.47	Ph
Coreidae	5.33 (7.54)	—	—	—	—	—	5.33	0.09	Ph
Hemiptera Larvae	21.33 (30.17)	—	—	—	5.33 (7.54)	80 (13.06)	106.66	1.88	Ph
Geophilomopha	—	5.33 (7.54)	16 (13.06)	5.33 (7.54)	10.67 (7.54)	—	37.33	0.66	Pr
Scolopendromorpha	—	—	—	5.33 (7.54)	—	—	5.33	0.09	Pr
Lithomorpha	5.33 (7.54)	—	—	—	—	—	5.33	0.09	Pr
Julida: Julidae	170.67 (86.98)	346.67 (168.49)	26.67 (7.54)	37.33 (19.96)	266.67 (83.99)	80 (72.74)	928.01	16.37	S
Orthoptera	—	—	5.33 (7.54)	32 (34.56)	—	32 (34.56)	69.33	1.22	Ph
Acridoidea	—	—	5.33 (7.54)	16 (22.63)	—	32 (34.56)	53.33	0.94	Ph
Orthoptera Larvae	—	—	—	16 (13.06)	—	—	16.00	0.28	Ph
Mantodea: Mantidae	—	—	—	5.33 (7.54)	—	—	5.33	0.09	Pr
Hymenoptera	144 (119.73)	192 (119.73)	144 (85.67)	106.67 (58.91)	250.67 (264.31)	53.33 (45.88)	890.67	15.71	O
Chalcidoidea	—	5.33 (7.54)	21.33 (7.54)	—	10.67 (7.54)	5.33 (7.54)	42.66	0.75	O
Formicidae	144 (119.73)	186.67 (125.53)	122.67 (78.75)	106.67 (58.91)	240 (260.95)	48 (47.1)	848.01	14.96	O
Diptera	357.33 (52.8)	133.33 (41.99)	320 (145.47)	122.67 (74.28)	298.67 (176.4)	192 (65.32)	1424.00	25.12	O
Culicidae	5.33 (7.54)	—	32 (26.13)	—	16 (13.06)	85.33 (37.71)	138.66	2.45	O
Diptera Larvae	352 (56.94)	133.33 (41.99)	288 (171.33)	122.67 (74.28)	282.67 (183.05)	106.67 (37.71)	1285.34	22.67	S
Trichoptera	—	—	5.33 (7.54)	—	5.33 (7.54)	—	10.66	0.19	O
Coleoptera	154.67 (7.54)	197.33 (32.88)	101.33 (27.19)	42.67 (15.08)	181.33 (45.88)	96 (13.06)	773.33	13.64	O
Elateridae	5.33 (7.54)	10.67 (15.08)	—	—	—	—	16.00	0.28	Ph
Staphylinidae	53.33 (19.96)	10.67 (7.54)	10.67 (7.54)	5.33 (7.54)	42.67 (19.96)	5.33 (7.54)	128.00	2.26	S
Chrysomelidae	5.33 (7.54)	5.33 (7.54)	—	5.33 (7.54)	—	10.67 (15.08)	26.66	0.47	Pr
Scarabaeidae	10.67 (7.54)	10.67 (7.54)	—	—	—	—	21.34	0.38	F
Carabidae	10.67 (15.08)	10.67 (7.54)	5.33 (7.54)	5.33 (7.54)	26.67 (27.19)	10.67 (7.54)	69.34	1.22	Pr
Curculionidae	16 (13.06)	—	16 (13.06)	5.33 (7.54)	10.67 (7.54)	21.33 (7.54)	69.33	1.22	Ph
Pselaphidae	5.33 (7.54)	—	—	—	5.33 (7.54)	—	10.66	0.19	Pr
Coccinellidae	—	5.33 (7.54)	—	—	—	5.33 (7.54)	10.66	0.19	O
Tenebrionidae	—	—	5.33 (7.54)	—	—	5.33 (7.54)	10.66	0.19	Ph
Silphidae	5.33 (7.54)	—	—	5.33 (7.54)	—	—	10.66	0.19	S
Lathridiidae	—	—	—	—	5.33 (7.54)	—	5.33	0.09	Ph
Scydmaenidae	—	5.33 (7.54)	5.33 (7.54)	—	—	—	10.66	0.19	Pr
Coleoptera Larvae	42.67 (15.08)	138.67 (52.8)	58.67 (49.46)	16 (13.06)	90.67 (27.19)	37.33 (7.54)	384.01	6.77	Ph
Dermaptera	5.33 (7.54)	—	—	—	21.33 (19.96)	—	26.66	0.47	O
Pseudoscorpiones	26.67 (37.71)	5.33 (7.54)	—	—	5.33 (7.54)	—	37.33	0.66	Pr
Araneae	69.33 (27.19)	101.33 (15.08)	101.33 (54.39)	42.67 (19.96)	170.67 (52.8)	112 (13.06)	597.33	10.54	Pr
Araneidae	5.33 (7.52)	10.67 (7.54)	16 (13.06)	—	21.33 (19.96)	—	53.33	0.94	Pr
Salticidae	—	5.33 (7.54)	—	—	16 (22.63)	5.33 (7.54)	26.66	0.47	Pr
Gnaphosidae	32 (26.13)	21.33 (15.08)	37.33 (41.99)	32 (13.06)	74.67 (27.19)	58.67 (7.54)	256	4.52	Pr
Linyphiidae	10.67 (15.08)	37.33 (7.54)	5.33 (7.54)	—	—	—	53.33	0.94	Pr
Clubionidae	—	—	10.67 (7.54)	—	5.33 (7.54)	5.33 (7.54)	21.33	0.38	Pr
Thomisidae	10.67 (15.08)	5.33 (7.54)	16 (13.06)	5.33 (7.54)	16 (22.63)	10.67 (7.54)	64	1.13	Pr
Agelenidae	—	—	5.33 (7.54)	—	—	5.33 (7.54)	10.66	0.19	Pr
Lycosidae	—	—	—	5.33 (7.54)	26.67 (15.08)	10.67 (15.08)	42.67	0.75	Pr
Oxyopidae	—	—	—	—	—	10.67 (15.08)	10.67	0.19	Pr
Zoridae	5.33 (7.54)	—	—	—	—	—	5.33	0.09	Pr
Liocranidae	—	10.67 (15.08)	5.33 (7.54)	—	5.33 (7.54)	5.33 (7.54)	26.66	0.47	Pr
Hahniidae	—	—	—	—	5.33 (7.54)	—	5.33	0.09	Pr
Opiliones: Phalangiidae	5.33 (7.54)	10.67 (7.54)	5.33 (7.54)	—	—	—	21.33	0.38	O
Isopoda: Oniscidae	—	—	—	5.33 (7.54)	5.33 (7.54)	—	10.66	0.19	S
Stylommatophora	10.67 (15.08)	10.67 (7.54)	5.33 (7.54)	16 (13.06)	26.67 (19.96)	5.33 (7.54)	74.67	1.32	O
Bradybaenidae	—	—	—	5.33 (7.54)	5.33 (7.54)	—	10.66	0.19	O
Ariophantidae	5.33 (7.54)	10.67 (7.54)	5.33 (7.54)	5.33 (7.54)	5.33 (7.54)	—	31.99	0.56	O
Carychiidae	5.33 (7.54)	—	—	5.33 (7.54)	16 (22.63)	5.33 (7.54)	31.99	0.56	O
Lepidoptera Larvae	26.67 (7.54)	80 (26.13)	—	—	53.33 (39.91)	21.33 (19.96)	181.33	3.20	Ph

Note: Ph: Phytophage; F: Fungivorous forms; Pr: Predators; S: Saprozoic; O: Omnivores [33]. The dominant taxa are the soil animal taxa which account for more than 10% of the total catch; the percentage between 1% and 10% is a common taxa; less than 1% are rare taxa. The data in the table represent the mean individual density (n = 3) and standard deviation (SD).

Table 3. Niche width of major soil fauna groups.

	Niche Width
Taxa of Soil Fauna	Spring	Summer	Autumn	Winter	Mean Value
Formicidae	4.31	4.90	4.88	1.60	3.92
Culicidae	3.90	2.08	0.00	0.00	1.50
Rhabditida	2.51	0.00	3.86	2.57	2.24
Collembola juvenile	3.03	1.80	5.38	4.54	3.69
Oribatida	3.34	4.40	5.55	3.64	4.23
Prostigmata	2.69	3.53	5.40	3.04	3.67
Julidae	3.38	2.00	4.28	0.00	2.42
Entomobryidae	2.28	2.28	1.80	1.98	2.08
Gnaphosidae	3.85	4.81	3.66	1.00	3.33
Diptera Larvae	4.31	3.44	4.76	4.13	4.16
Coleoptera Larvae	2.91	4.67	3.91	3.20	3.67
Thripidae	0.00	1.80	3.38	2.09	1.82
Lepidoptera Larvae	2.67	2.47	1.80	1.80	2.18
Staphylinidae	1.28	3.60	1.00	2.00	1.97
Cicadellidae	1.00	3.31	1.00	1.00	1.58
Carabidae	2.67	1.80	3.60	0.00	2.02
Curculionidae	1.00	2.57	3.00	1.00	1.89
Thomisidae	2.67	3.56	0.00	1.00	1.81

Note: “0” indicates that the taxa did not appear in the season.

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Qin, J.; Liu, C.; Ai, N.; Zhou, Y.; Tuo, X.; Nan, Z.; Shi, J.; Yuan, C. Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau. Land 2022, 11, 1958. https://doi.org/10.3390/land11111958

AMA Style

Qin J, Liu C, Ai N, Zhou Y, Tuo X, Nan Z, Shi J, Yuan C. Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau. Land. 2022; 11(11):1958. https://doi.org/10.3390/land11111958

Chicago/Turabian Style

Qin, Jiafeng, Changhai Liu, Ning Ai, Yongwei Zhou, Xianghui Tuo, Zhengzheng Nan, Jiahao Shi, and Caixia Yuan. 2022. "Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau" Land 11, no. 11: 1958. https://doi.org/10.3390/land11111958

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Community Characteristics and Niche Analysis of Soil Animals in Returning Farmland to Forest Areas on the Loess Plateau

Abstract

1. Introduction

2. Materials and Methods

2.1. Overview of the Study Area

2.2. Collection of Soil Fauna

2.3. Identification of Soil Fauna

2.4. Statistical Analysis

3. Results

3.1. Community Structure of Soil Animals

3.1.1. Composition of Soil Animal Community

3.1.2. Diversity of Soil Animals

3.2. Main Soil Animal Niche

3.2.1. Niche Width of Main Soil Fauna

3.2.2. Niche Overlap Values of Major Soil Fauna

4. Discussion

Composition and Structure of Soil Animal Community

5. Conclusions

Author Contributions

Funding

Data Availability Statement

Conflicts of Interest

Appendix A. Full Taxa List of Soil Fauna

References

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