Soil nematode communities as soil health indicators in rare earth mining areas of different restoration ages

Environmental variables such as soil moisture and phosphorus (P) might influence above- and below-ground biodiversity. In this study, we investigated the rarely reported individual and interactive multifactor effects of soil moisture and phosphorus addition with the type of above-ground tree species (biological interactions) on the soil nematode community structure. We established a completely randomized experimental design with two plant types (N2-fixer and non-nitrogen fixer) and different combinations of water treatments and P additions (i.e., water with P addition, water only, drought with P addition, and drought only) in a greenhouse and investigated their effects on the soil chemical properties and nematode community. Soil samples were collected at the end of the experiment and were analyzed for soil moisture content (SM), available phosphorus (aP), nitrate nitrogen (NO3−–N), ammonium nitrogen (NH4+–N), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and nematode community. The following trophic groups were assigned to the nematodes: bacterivores (Ba), fungivores (Fu), omnivores–predators (Op), and plant parasites (PP). The channel index (CI), enrichment index (EI), maturity index (MI), genus richness (GR), and Simpson dominance (Ig) were adopted to indicate the indices of the nematode food web. Phosphorus addition and its interaction with water treatments had no statistically significant effects on the soil nematode community, but there were significant decreasing (p < 0.05) effects of P addition on the total density of nematodes of the N2-fixing tree under optimum water treatment. There were no significant interactive effects of P addition and water treatments on all the trophic groups, but plant type, water treatments, and their interactions significantly affected the density of most nematode trophic groups. The total nematode abundances of bacterivores, plant parasitic, omnivores, and enrichment index were significantly higher in the N2-fixers than in the non-nitrogen-fixing tree. Soil nematode abundance and community composition were more affected by the plant type than by the P addition and its interaction with water treatments. Drought exerted adverse effects on the total density of soil nematodes, the dominant genera, and the trophic groups. This study demonstrated that the rate of drought impact hinges more on the type of tree and that N2-fixing tree could still maintain the soil food web structure irrespective of the environmental changes.

Effects of tillage and residue management on soil nematode communities in North China

Global warming and drying are important environmental issues. Our study aimed to investigate how warming and precipitation changes affect soil nematode communities in an Inner Mongolian desert steppe for 10 years. Soil nematodes were extracted by the Baermann funnel method. Changes in the nematode communities under artificial warming and precipitation conditions were assayed by analyzing their abundance and ecological indices. Soil nematode abundance decreased significantly by 37.47% under artificial warming; however, there was no significant effect of warming on the nematode community diversity. As for precipitation experiment, the decreased precipitation eliminated some of non-dominant nematode genera, such as Pratylenchus, Helicotylenchus, and Aphelenchus. It caused not only a significant decrease (37.65%) in soil nematode abundance but also a more structured food web and shorter food chain. However, nematode faunal analysis indicated that the soil nematode community was more resistant to drought. Both soil nematode abundance and community diversity increased significantly as increase of precipitation. In particular, the abundance of plant parasitic nematodes increased by 46.69%, which may due to the increase in total nitrogen content in soil. Nematode faunal analysis showed that increased precipitation improved soil environment for the nematodes, and increased food web connectivity and food chain length. However, bacterivorous nematode abundance decreased by 74.39%, and the decomposition pathway of the nematode community had switched from the bacterial channel to the fungal channel. In the Inner Mongolian steppe, both climate drying and warming had negative impacts on soil nematode abundance; however, only drying affected nematode community diversity and food web structure and slowly changed nematode ecological functions. Increased precipitation may aid soil nematode community recovery.

Effects of long-term turfgrass management practices on soil nematode community and nutrient pools

The combined effects of warming and increased nitrogen (N) deposition in various ecosystems have become global issues. We used high‐throughput sequencing in an 8‐year field experiment to evaluate the impacts of the interactions between warming and nitrogen addition on soil nematode communities in a desert steppe. The soil nematode community presented with a certain degree of tolerance to warming. Warming mainly altered soil nematode diversity and community stability in deep soils whereas nitrogen addition primarily affected the nematode community in surface soils. Moreover, warming interacted with nitrogen addition exacerbated its negative effects on nematode richness and diversity. A Mantel analysis showed that soil pH was significantly negatively correlated with soil NH4+ and NO3− content. All three soil physicochemical (pH, NH4+ and NO3−) parameters were significantly correlated with desert steppe soil nematode community structure. Based on network and relative abundance analyses, we determined that Paratylenchus, Cervidellus, and Acrobeloides were the major hub soil nematode genera responding to soil warming and nitrogen addition in a desert steppe. The present study comprehensively analyzed the responses of desert steppe soil nematode communities to warming and nitrogen addition and provided an exemplar for studying the impact of environmental factors on soil nematodes communities worldwide.

Plant species effects on soil nematode communities in experimental grasslands

A one-time, large application of biochar (charcoal) could increase soil carbon (C) content and improve overall soil quality. It is known that nematodes have effects on soil organic matter and nutrient cycling and are plant diseases; moreover, nematodes affect nutrient mobilization in C-rich soil conditions; however, information is scant on the effect of biochar addition on nematode communities. Therefore, the objective of this field study was to evaluate the influence of sugar maple hardwood biochar on soil nematode communities and assess the relation among soil nematode communities and soil nutrient concentrations. Nematode communities were sampled and identified in soils without biochar application and soil amended with an application of 8% by weight (equivalent to 160 Mg ha−1). The application of 8% biochar did not change the abundance of nematodes but affected some nematode communities. Compared to the unamended soil, biochar-amended soil had lower plant-parasitic nematode populations and higher abundance of predatory nematodes. The Shannon diversity index (H’) was lower, and the maturity index (MI) was higher with a mean value of 2.38 with biochar addition compared to 2.21 in unamended plots. Higher soil acidity and addition of substantial amounts of magnesium, calcium, potassium, and manganese in the biochar-amended soils were recorded after biochar application.

Land use and temperature shape the beta diversity of soil nematodes across the Mollisol zone in northeast China

Changes in diversity patterns and assembly processes of soil nematode communities during forest secondary succession on the Loess Plateau

Higher taxa vs. functional guilds vs. trophic groups as indicators of soil nematode diversity and community structure

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health.Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure.At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding.Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2–5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments.We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

Summary The study of soil nematode communities is a powerful tool that has been widely used as an indicator of soil health. This study explored whether soil nematode composition of different land use types could be used as a baseline to indicate the soil health of both natural and anthropogenic ecosystems. The soil nematode community compositions were documented for five land use types in tropical China: bare land, secondary forest, old forest, eucalyptus plantation and litchi orchards. The first three land use types are natural ecosystems and considered as a vegetation succession, whereas the other two are anthropogenically managed ecosystems. The vegetation succession from bare land to secondary and old forests increased soil nematode abundance, diversity, diversity-weighted abundance and complexity of community structure. During the wet season, the abundances of the total nematodes, bacterivores, fungivores and herbivores were significantly lower in eucalyptus plantation and litchi orchards than in secondary and old forests, but higher than in bare land. During the dry season, the abundances of the total nematodes and each trophic group were greatest in orchards. The pattern of the diversity-weighted abundance of each nematode trophic group was similar to that of nematode trophic group abundance. The results indicate that soil nematode communities of different land use types could be used for comparison of soil health conditions in natural and managed ecosystems. Particularly, the soil health conditions as indicated through nematode communities of the two managed ecosystems were not as good as those of secondary and old forests, whereas litchi orchards might have better soil health conditions than eucalyptus plantations in tropical China.

Effects of different carbon inputs on soil nematode abundance and community composition

Effects of wild boar grubbing on the soil nematode community subject to seasonal variation in a broad-leaved Korean pine forest in Northeast China

The establishment of Medicago sativa artificial grasslands is an important practice of grassland vegetation restoration in the Loess Plateau. Understanding community characteristics of soil microbes and nematodes can provide important information for evaluating and controlling ecolo-gical and environmental effects of vegetation restoration. In this study, we used M. sativa artificial grasslands with four different cultivation years (1, 2, 6 and 12 years) in southern Ningxia mountainous region, with a farmland and a natural grassland as control, to explore changing trends of the two biological communities during artificial grassland restoration in semi-arid region of the Loess Plateau. The results showed that: 1) After the conversion of farmland to M. sativa grassland, Chao1, ACE and Shannon diversity indices of soil bacterial community increased firstly and then decreased, which reached the maximum after six years of M. sativa grassland establishment. For soil fungal community, Shannon diversity index was lower in 6 and 12 year-old M. sativa grasslands than in the other two artificial grasslands, and the community composition differed across restoration years. 2) With the increases of restoration years, the abundance of soil nematodes showed a similar changing trend with Shannon diversity index of bacterial community. The composition of nematode community did not greatly differ between the 6-year-old M. sativa grassland and farmland, while that in 12-year-old artificial grassland was more similar to that in natural grassland. The proportion of bacterivorous and plant-feeding nematodes, as well as plant parasitic index and nematode channel index of nematode community,were increased, while the proportion of fungivores and omnivores-predators and maturity index were decreased. 3) During the restoration, changes in soil organic carbon, total nitrogen and available phosphorus greatly affected soil microbial community, which could further influence soil nematode community. There were significant correlations between dominant microbial phyla and trophic groups of soil nematodes, implying the possible effects of soil microbes on nematode community. In M. sativa artificial grassland with different establishment years, changes in plant biomass and diversity might significantly affect soil nematode and microbial communities through affecting their food conditions.