This paper introduces the species diversity and the functions of soil nematodes. Nematodes are ubiquitous with diverse feeding behaviors and life strategies. The diversity of feeding behaviors and some intrinsic properties result in the complex biotic interaction between soil nematodes and other soil biota, which greatly affects the ecosystem functions. However, the research on the species diversity of soil nematodes and their ecosystem functions is still inadequate. To understand the role of soil nematodes in the ecosystem requires: (1) the combination of laboratory microcosm study and field mesocosm experiments; and (2) the combination of biodiversity survey and functional analysis of different groups.

Soil biodiversity has been one of the foci in the soil ecological research field. Soil biota can change the physical, chemical and biological characters of soil in different ways. In farmland ecosystems, soil organisms are main regulators in the decomposition, nutrient mineralization and other ecological processes of soil. Soil nematodes are the most abundant metazoan, which have various types of life-history and feeding habits, and play a key role in soil food web. This paper introduces the main factors influencing soil nematode diversity in farmland ecosystems, reviews the present situation in the nematode diversity research field and presents the research prospect of nematode diversity in the future. We propose to integrate the life strategy approach and trophic group classification to obtain a better understanding of nematode diversity and their functions, so as to use nematodes as effective bioindicators in farmland ecosystems.

In this paper, the soil biodiversity and its functioning in ecosystem were briefly summarized, and the history and development of the discipline of soil biology were also reviewed. Meanwhile, I pointed out some issues on soil biology to be addressed for a few years to come. Due to the importance of soil biodiversity to the maintenance of ecosystem functions but inadequate study on soil biota in China, a series of articles on soil biota were collectively published in this issue of Biodiversity Science. The objectives of this issue were to enable the Chinese scientists to better understand the functions of soil biodiversity and to stimulate the interest of young scholars in the discipline of soil biology. The ultimate goal was to push forward the research and development of soil biology in China and to apply the knowledge and techniques of soil biology in the development of national economy.

In order to understand the relationship between soil arthropod community structure and floor litter at different successional stages of tropical forests, we surveyed the floor litter and the soil arthropods in a 23-year secondary forest, a 35-year secondary forest and a primary seasonal rainforest of Xishuangbanna, SW China in September 2001. Soil arthropods were extracted from the litter by Tullgren funnel method. The results showed that both the quantity and quality (N and C/N) of litter in the 35-year secondary forest were higher than those of the 23-year secondary forest and the seasonal rainforest. Acari and Collembola were dominant groups (> 80%), while ants, Coleoptera, Diptera, and Archaeognatha were common groups in the three forests. A higher individual density and relative individual density of soil arthropods were found in the 35-year secondary forest (10,067 ind./m2 and 22.72 ind./g dry litter) compared to the seasonal rainforest (5,654 ind./m2 and 18.44 ind./g dry litter) and 23-year secondary forest (2,881 ind./m2 and 5,818 ind./g dry litter). Pielou and Shannon-Wiener index of soil arthropod community were significantly higher in the 23-year secondary forest, while the richness (Margalef index) peaked in seasonal rainforest, and the domi-nance index (Simpson index) in 35-year secondary forest was the highest. The soil arthropod community composition was similar among the three forests. The individual density (ind./m2) of soil arthropods were positively correlated with floor litter mass in three forests, and they were correlated with the standing stock of N of the floor litter in 23-year secondary forest, and the standing stock of N of the floor woody detritus in seasonal rainforest. We conclude that the development of soil arthropod community in tropical forests is closely related to vegetation succession, and the soil arthropod community structure can be regulated through plant litter during the forest succession process, but other environmental effects including predator effect and human disturbance should not be ignored.

The springtails are widespread small to tiny arthropods in soil ecosystem. They play important roles in the circulation of soil materials, development of soil, formation of soil micro-structure, improvement of soil physical and chemical properties, and the maintenance of soil living community. The diversity, community structure, and species composition of springtails in the soil reflect the status of soil quality and con-tamination. The important roles of springtails in the soil ecosystem, their potential values in the ecological practices and the recent advances and prospects are introduced in the present paper.

In order to provide scientific evidence of soil health for city planning, the diversity and composition of the soil animal community of the site of World Exposition Shanghai China 2010 were investigated. A total of 10,765 soil animal individuals belonging to 23 groups of soil animals were collected, of which Acarina was the dominant group of soil meso- and micro-fauna, and Collembola was the secondary one. As for soil macrofauna, Oligochaeta was the dominant group, while Isopoda, Coleoptera, and Gastropoda were the secondary ones. The results indicated that soil animals were abundant at this site. The soil animals reduced along with the increasing soil depth, and their distribution varied significantly at different sampling sites.

We used generic number, individual density, biodiversity, and functional group index to analyze the effect of mowing practice on soil nematode community in alkalinized grasslands of Leymus chinensis in Songnen Plain, Northeast China. A total of 8,335 soil nematode individuals were collected, belonging to two classes, seven orders, 23 families, and 40 genera. The results indicated that the generic number and individual density of soil nematodes were significantly lower in the land under mowing practice (MP) treatment than that under fencing enclosure (FE) treatment, whereas the diversity index showed no significant difference between the two treatments. The results also suggested that PPI/MI was sensitive to mowing practice, which changed the composition of functional groups of soil nematodes, especially that of free-living soil nematodes.

The seasonal and vertical distribution of soil nematode communities under three contrasting land uses, i.e., cropland, abandoned cropland and woodland, was conducted in an aquic brown soil. The results showed that land-use types affected the spatio-temporal distribution of soil nematodes and their dominant genera, and different dominant genera showed different responses to land uses. In the abandoned cropland and woodland, most dominant genera were present in the 0–20 cm layers and Chiloplacus was mainly distributed in the 5–30 cm layers, while in the cropland Pratylenchus exhibited an even distribution from the 0–5 to the 40–50 cm depths. Soil environmental parameters under different land uses could influence soil nematodes; soil porosity, total organic C, total N and the C/N ratio were found to positively influence the abundance of some dominant genera in the present study. The faunal profiles revealed that the environmental stability and the homeostasis of the abandoned cropland and woodland lead to higher levels of community structure and the soil food web tend to succeed to maturity. Nematode faunal analyses were found to be a useful method for interpreting the stress or/and nutrient conditions under different land uses.

As one of the key soil invertebrates, earthworms can greatly impact soil processes, and thus was named as “ecosystem engineer”. Earthworm activities such as feeding, digestion, excretion, and burrowing, facilitate the formation of various drilosphere in their guts or soils around, through which they alter the biological, chemical and physical processes of the ecosystem. Earthworms act as consumer, decomposer and modulator in ecosystem. The ecological functions of earthworm include: (1) effects on key soil ecosystem processes such as decomposition of soil organic matters and nutrient cycling; (2) effects on soil chemical and physical properties; and (3) interaction with plants, microorganisms and other animals. Earthworm activities and their functions in ecosystem are determined by various factors such as ecological groups of earthworms, population size, vegetation, parent materials of soil, climate, time scale, and history of soil utilization. The development of earthworm ecology was constrained by the complex feature of soil, the scarce knowledge of natural history and biogeography of earthworms, and the low efficiency of approaches in field manipulation of earthworm community. We suggest that new technologies such as the C and N isotope technique for nu-trient cycling and the image analysis approaches for soil micro-structure should be applied on earthworm ecological research in order to better understand the functions of earthworms.

The ecological functions of soil fauna have attracted widespread interest from ecologists during the past two decades. A growing number of evidences show that the soil fauna interact with microorganisms and play important roles in regulating soil ecosystem processes and plant growth. This review addresses the issue of how bacterial- and fungal-feeding nematodes influence soil microorganisms, nitrogen mineralization and plant growth. Most studies suggest that bacterial- and fungal-feeding nematodes stimulated soil nitrogen mineralization and promoted plant growth. The mechanisms underlying these effects are the impact of nematode grazing on microorganisms and the release of nutrients from consumed microbial biomass. How-ever, these effects vary with different nematode species, microorganism species, plant species and C/N ratios of substrates, and are influenced by complex interactions between different trophic groups of nematodes as well as other soil fauna. Future studies should (1) enhance our understanding about the mechanistic basis of the interaction of nematodes, microorganisms and plants; (2) address more complex interactions between different trophic groups of nematodes and other soil fauna; (3) examine the ecological roles of soil nematodes at a longer temporal scale; (4) compare different ecosystems to understand the ecological roles of soil nematodes at a broader spatial scale; and (5) predict the responses and feedbacks of soil nematodes to atmospheric drivers of global changes.

Soil health is important for the sustainable development of terrestrial ecosystem. In this review, we summarizes the relationship between soil quality and soil microbial characteristics such as soil microbial community structure, soil microbial biomass and soil enzymatic activity in order to illustrate the function of soil microbial characteristics as bio-indicators of soil health. Many studies have showed that the soil nutrient is correlated with the quantity or the composition of bacteria, fungi and actinomycetes in soils. In general, higher ratio of soil bacteria indicates better soil quality and higher soil nutrient content. Soil microbial bio-mass is closely correlated with soil organic carbon, and the ratios of soil microbial biomass carbon to soil or-ganic carbon(C_mic : C_org) and microbial metabolic quotient (qCO2) reflect the use efficiency of soil organic C. The activity of soil enzymes are positively correlated with soil microbial biomass carbon and nitrogen. Therefore, soil microbial characteristics reflect the changes of soil quality and thus can be used as bio-indicators of soil health.

In order to evaluate the process of ecological restoration in Dongting Lake region, we surveyed the community structure and diversity of soil animals in October 2005. A total of 8,484 individuals, belonging to five phyla and 11 classes, were obtained from three typical habitat types, i.e., wetland restored from farm-land, farmland, and original wetland. Twenty-six species were obtained from wetland restored from farmland, of which Nematode and Acarina accounted for 66.97%, while 28 species were collected from farmland, of which Nematode and Araneae occupied 61.79%. However, only 13 species were found in the original wet-land, of which Gastropoda was the absolutely dominant group, accounting for 79.89%. The results analyzed using diversity indices (H′, E, C, D, C_j) indicated that: (1) Complexity index (C_j ) is manifested better than H' in representing the complexity and the diversity of animal communities; (2) Community diversity index (H′), had a closer relationship with evenness index (E) (P<0.05); (3) Wetland restored from farmland and the farmland were richer in soil animal taxa than the original wetland (P<0.01). In terms of soil animal individu-als, there were far more in the farmland than in the original wetland (P<0.01), whereas no significant differ-ence (P>0.05) was found between the wetland restored from farmland and in the original wetland. The results indicated that the ecological restoration process in Dongting Lake region was fairly slow and inefficient.