Plant-feeding Nematodes Research Articles

Assessing the Effectiveness of Rotation Growing of Industrial Hemp and Alfalfa in Post-Mining Agricultural Reclamation: Using Soil Fauna as an Indicator

The reclamation of post-mining land for agricultural purposes has continued to be a big challenge. Our study concerns the use of soil microfauna (nematodes) and mesofauna (mites and springtails) as indicators of soil quality after 6 years of agricultural reclamation of a post-mining area in west–central Poland. A new method, which involves rotation growing of industrial hemp (H) and alfalfa (A) and incorporating the resulting biomass into the soil, was used to reclaim two sites (5 and 15 years after mining) representing different types of post-mining deposits (clayey and sandy). On each site, two plots were established, where each crop was grown for three years, but in a different order during the rotation cycle (3H3A and 3A3H). The results showed significant differences in the abundance and structure of the fauna communities between 3H3A and 3A3H reclamation practices, as well as between the reclaimed plots and non-reclaimed (NR) plots, where spontaneous succession proceeded. The three animal groups were more abundant in the reclaimed soil compared to the NR soil. The highest densities for nematodes were observed in the 3H3A plots and for the mesofauna in the 3A3H plots. The reclamation practices had a positive effect on groups involved in the regulation of C and N mineralisation, particularly bacterial- and hyphal-feeding nematodes and oribatid mites, and a negative effect on plant-feeding nematodes and euedaphic collembolans. The finding that most of the parameters of the studied biota had values resembling those of agricultural soils after 6 years of reclamation clearly indicates the effectiveness of the applied practices for transforming degraded land into soils that mirror soils under agricultural use.

Sperm development and structure in Bursaphelenchus luxuriosae (Nematoda: Aphelenchoidea: Aphelenchoididae)

Summary Sperm development and structure in the wood-inhabiting fungal and plant-feeding nematode, Bursaphelenchus luxuriosae, were studied using transmission electron microscopy to evaluate interspecific similarities and differences of spermatozoa in nematodes. In general, spermatogenesis in B. luxuriosae fits the ‘rhabditid’ pattern supported by morphological and phylogenetic analysis of the order Rhabditida. Spermatocyte development includes formation of complexes of fibrous bodies (FBs) with membranous organelles (MOs), the complexes dissociate in the spermatids into separate components, and the immature sperm contain MOs but lack FBs, which transform into a dense matrix of sperm cytoplasm. The female spermatheca contains mature spermatozoa as bipolar cells subdivided into a pseudopod devoid of organelles and a main cell body containing a nucleus without a nuclear envelope, numerous mitochondria, and peripheral MOs as pouches opening to the exterior via pores. Data on B. luxuriosae are used for analysis of variable quantitative and morphological characteristics of spermatozoa in Aphelenchoidea. General size of spermatozoa and their MOs have little value for comparative analysis. The MO knobbles look uniform in immature spermatozoa of each aphelenchoidid species studied and may be considered as a taxonomically specific ultrastructural feature. The presence or absence of FBs in immature spermatozoa demonstrates the diagnostic value of the aphelenchoidid sperm structure at the species level. Analysis also shows close similarity of spermatozoa in Bursaphelenchus spp. and Caenorhabditis elegans, the model species with comprehensive data on sperm biology. This may be used to identify new ways for the control and suppression of harmful nematode species such as B. xylophilus.

Artificial light at night (ALAN) causes shifts in soil communities and functions.

Artificial light at night (ALAN) is increasing worldwide, but its effects on the soil system have not yet been investigated. We tested the influence of experimental manipulation of ALAN on two taxa of soil communities (microorganisms and soil nematodes) and three aspects of soil functioning (soil basal respiration, soil microbial biomass and carbon use efficiency) over four and a half months in a highly controlled Ecotron facility. We show that during peak plant biomass, increasing ALAN reduced plant biomass and was also associated with decreased soil water content. This further reduced soil respiration under high ALAN at peak plant biomass, but microbial communities maintained stable biomass across different levels of ALAN and times, demonstrating higher microbial carbon use efficiency under high ALAN. While ALAN did not affect microbial community structure, the abundance of plant-feeding nematodes increased and there was homogenization of nematode communities under higher levels of ALAN, indicating that soil communities may be more vulnerable to additional disturbances at high ALAN. In summary, the effects of ALAN reach into the soil system by altering soil communities and ecosystem functions, and these effects are mediated by changes in plant productivity and soil water content at peak plant biomass. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Combined effects of aboveground herbivores and belowground microorganisms on dynamics of soil nematode communities in grassland mesocosms

Nematodes are the most abundant animals in soil. They are active in all trophic levels and functionally important for plant growth and plant diversity. Nematode community structure not only can be directly influenced by other belowground organisms such as soil microbes via trophic interactions, but also indirectly by aboveground organisms like herbivores through plant-mediated aboveground-belowground linkages. In the current study, by introducing foliar-feeding aphids (Rhopalosiphum padi) and soil microbial suspensions to mesocosms planted with 12 grassland plant species and where an identical nematode community was introduced in all mesocosms, we aimed to investigate the individual and combined effects of soil microbes and foliar herbivores on the dynamics of plant and the soil nematode community. Introduction of aphids reduced shoot and root biomass of the plant community, and in particular decreased the proportional biomass of the dominant plant species Anthoxanthum odoratum, resulting in a higher diversity of the plant community but without affecting the nematode communities. In contrast, the inoculation of soil microbes did not significantly alter plant composition structure, but it reduced the total nematode abundance and enhanced nematode diversity by increasing the abundance of carnivorous nematodes and decreasing the abundance of plant-feeding nematodes. There were no significant aboveground-belowground interactions in the current study via effects of aphids on the soil nematode communities or via soil microbes and nematodes on the plant communities. Collectively, our study indicates that soil nematode communities in grasslands can be strongly steered by soil microbial inoculations but weakly influenced by aboveground herbivory despite its resulting changes in plant communities, notwithstanding that these effects appeared to be largely independent.

Diversity of woody plant nematodes in specially protected biocenosis of Zarafshan Mountain, Uzbekistan

Abstract. Narzullayev S, Kambarov S, Mirzaev U, Tursunova S. 2023. Diversity of woody plant nematodes in specially protected biocenosis of Zarafshan Mountain, Uzbekistan. Biodiversitas 24: 3145-3151. Very little information exists on nematodes' diversity and ecological characteristics in small artificial forests. This article provides information on the diversity of the nematode fauna, bioecological characteristics, and species distribution by biotopes of fruit trees growing in the biocenoses of the Omonkutan National Nature Park in the Western Zarafshan mountain range. As a result of the research, 62 species of nematodes were recorded in the nematode fauna of fruit trees. These species were analyzed taxonomically and ecologically. It was determined that the species in the fauna belong to two classes and five orders of the Nematoda type. They are divided into five large and several small groups according to their ecological characteristics. Among the ecological groups, omnivorous and plant-feeding nematodes are the dominant groups in terms of the number of species. The diversity of nematodes was high in the 0-15 and 15-30 cm soil layers. It turned out that the diversity in different biotopes is related to the ecological characteristics of nematodes. In particular, herbivorous nematodes accounted for 72.2% of nematodes in the root system. An increase in the diversity of nematodes was observed in the rhizosphere soil layers. A sharp increase in the number of species and individuals of omnivorous nematodes and bacteriotrophs was observed in the 0-15 cm soil layer, and this trend was also preserved in the 15-30 cm layer. The species richness and diversity (according to the Shannon and Simpson indices) were the lowest in vegetative parts of plants. As a result of the research, it became clear that the diversity of soil nematodes is completely dependent on their trophic characteristics.

Plant clustering generates negative plant–soil feedback without changing the spatial distribution of soil fauna

Abstract. The spatial distribution of resources affects ecological processes at all levels of biological organization. However, it remains to be tested how the spatial configuration of belowground resources affects the community dynamics of soil organisms and resulting plant–soil feedbacks. We used Agrostis stolonifera plants in different spatial configurations in mesocosms to study the dispersal patterns of soil nematodes and rotifers. Plant–soil feedbacks were later assessed by re-sowing the mesocosms with Lolium perenne and Plantago lanceolata after removing all the initial A. stolonifera plants from the mesocosms. Bacterial-feeding nematodes and rotifers spread fast, whereas plant-feeding nematodes barely dispersed from the release sites. These spread patterns of nematodes and rotifers depended on the life-history traits and not on the spatial pattern of the plants. However, more clustered plants developed a higher total biomass and caused a reduced growth of the subsequent vegetation. Our results demonstrate that the mere spatial pattern of a single plant species can alter the strength of plant–soil feedbacks. This has important implications for understanding the impact of planting or replanting schemes and other changes in the spatial configuration of plants on long-term vegetation development and succession.

Plant genetic diversity affects multiple trophic levels and trophic interactions

Intraspecific genetic diversity is an important component of biodiversity. A substantial body of evidence has demonstrated positive effects of plant genetic diversity on plant performance. However, it has remained unclear whether plant genetic diversity generally increases plant performance by reducing the pressure of plant antagonists across trophic levels for different plant life forms, ecosystems and climatic zones. Here, we analyse 4702 effect sizes reported in 413 studies that consider effects of plant genetic diversity on trophic groups and their interactions. We found that that increasing plant genetic diversity decreased the performance of plant antagonists including invertebrate herbivores, weeds, plant-feeding nematodes and plant diseases, while increasing the performance of plants and natural enemies of herbivores. Structural equation modelling indicated that plant genetic diversity increased plant performance partly by reducing plant antagonist pressure. These results reveal that plant genetic diversity often influences multiple trophic levels in ways that enhance natural pest control in managed ecosystems and consumer control of plants in natural ecosystems for sustainable plant production.

Ultrastructural detection of intracellular bacterial symbionts in the wood-inhabiting nematode Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae)

Summary Ultrastructural observations of the wood-inhabiting fungal- and plant-feeding nematode, Bursaphelenchus mucronatus, revealed intracellular bacteria in the male and female gonads. In males, bacteria were present inside the testis epithelial cells, spermatocytes, spermatids and immature spermatozoa. Spermatheca of females contained amoeboid pseudopod-bearing mature spermatozoa with bacteria closely associated with the sperm nucleus. Tissues of the females studied were free from bacteria. The gram-negative bacteria in their localisation, size, ultrastructure, and especially characteristic internal bundle of parallel filaments, were identified preliminary as related to the genus Cardinium (Bacteroidetes), which includes obligate endosymbionts of diverse arthropods and is known to be associated with several species of plant-parasitic nematodes.

Concentration-Dependent Impacts of Microplastics on Soil Nematode Community in Bulk Soils of Maize: Evidence From a Pot Experiment

Agricultural land soils have become a source and sink for microplastics. Due to the low recycling rate, long durability, and small size, microplastics pose a potential risk to soil fauna, which are critical for maintaining healthy soil. However, whether and how would microplastics affect soil biodiversity and ecological functioning is not well-understood. Soil nematodes are valuable indicators of the soil food web. In the present study, the abundance, diversity, community composition, maturity indices, soil food web indices, and metabolic footprints of soil nematodes in bulk soils of maize were utilized to indicate the potential impacts of polypropylene (PP) microplastic pollution on soil fauna using a soil-incubation experiment in a climate-controlled chamber with four concentration levels of microplastic pellets (0%, 0.5%, 1%, and 2%, w/w) added to loess soil collected from the Loess Plateau in China. Soil sampling was conducted at the fully ripe stage of maize. Twenty-nine genera of nematodes, including thirteen genera of plant-feeding nematodes, seven genera of bacterial-feeding nematodes, five genera of fungal-feeding nematodes, and four genera of omnivorous nematodes were recovered from soil samples. Microplastic concentration negatively affected the abundance, diversity (including genus richness, Margalef’s richness, Shannon–Wiener index, and Simpson’s dominance index), sigma maturity index (∑MI), structural index, and metabolic footprints. The abundances of plant parasites, bacterivores, fungivores, and omnivores in 2% soils were reduced by 90.16%, 76.06%, 82.35%, and 100%, respectively, in comparison with those of control. The major drivers of soil nematode communities in bulk soils of maize at a depth range of 0–20 cm were the soil pH, soil organic carbon content, C/N, and TP content. In conclusion, the addition of 200 μm-sized PP microplastic pellets negatively affected the soil nematode community and associated ecological functioning under greenhouse conditions.

Characterization of three plant or fungal feeding nematodes (Nematoda, Rhabditida, Tylenchomorpha) from coastal dunes in Spain including the SEM study of these species

Three known species, Aphelenchus avenae, Ditylenchus myceliophagus and Tylenchorhynchus aduncus (Rhabditida, Tylenchomorpha), are described from sand coastal dunes in Spain associated to the rhizosphere of xerophilic plants. A. avenae is characterized by having stylet with 16–22 µm long, pharyngeal dorsal gland overlapping the intestine, postvulval uterine sac about 2.5 times the body diameter, female tail short conoid with rounded tip bearing the phasmid and male bursa well developed. D. myceliophagus is characterized by having lateral field with four incisures, stylet 7–8 µm long, basal bulb irregularly pyriform, tail of both sexes similar with rounded tip and bursa of the male reaching about three-quarters of tail length. T. aduncus is characterized by its lateral field with six incisures, stylet 15–18 μm long, spicules with bifurcate tip and distal ventral crest, and gubernaculum with hook-like manubrium. New morphological, including SEM study, and morphometrical data are included for the three species. Also, phylogenetic analysis based on 18S and 28S rDNA is included for two of the species studied. Additionally, two species belonging to the superfamily Aphelenchoidea are transferred to other genera: Aphelenchus assamensis to the genus Aphelenchoides and Aphelenchoides dhanachandi to the genus Potensaphelenchus.

Depth-structuring of multi-kingdom soil communities in agricultural pastures.

The biodiversity and structure of deep agricultural soil communities are poorly understood, especially for eukaryotes. Using DNA metabarcoding and co-occurrence networks, we tested whether prokaryote, fungal, protist, and nematode biodiversity declines with increasing depth (0-0.1, 0.3-0.5, and1.1-1.7m)inpastoral soil; whether deep soil organisms are subsets of those at the surface; and whether multi-kingdom networks become more interconnected with increasing depth. Depth-related richness declines were observed for almost all detected fungal classes, protist phyla, and nematode orders, but only 13 of 25 prokaryote phyla, of which nine had increasing richness with depth. Deep soil communities were not simply subsets of surface communities, with 3.8%-12.2% of eukaryotes and 13.2% of prokaryotes detected only in the deepest samples. Eukaryotes mainly occurred in the upper soil layers whereas prokaryotes were more evenly distributed across depths. Plant-feeding nematodes were most abundant in top soil, whereas bacteria feeders were more abundant in deep soil. Co-occurrence network structure differences suggested that deep soil communities are concentrated around scarce niches of resource availability, in contrast to more spatially homogenous and abundant resources at the surface. Together, these results demonstrate effects of depth on the composition, distribution, and structure of prokaryote and eukaryote soil communities.

Nematode communities indicate anthropogenic alterations to soil dynamics across diverse grasslands

Nematode communities are meaningful biological indicators of soil health and soil processes across different grassland types and management practices and analyses of nematode communities provide insight into structure, function, and sensitivity or resilience across multiple ecosystems. In three model grasslands: meadow steppe (MS), typical steppe (TS), and alpine meadow (AM), this current research examined responses of soil nematode communities and related edaphic characteristics to grazing, mowing, and crop cultivation at two soil depths. The research fills a critical knowledge gap by resolving multidirectional influences between local conditions, grassland management practices, and nematode communities. Across grassland types, nematode abundance in AM was greater than MS and TS grasslands, and nematodes were more abundant near the soil surface. Cultivation resulted in greater nematode abundance compared to all other management practices, and generally, bacterivores were the most dominant nematode trophic group. The TS and MS grasslands had relatively more bacterivores, exhibiting substantial influences on soil mineralization and organic matter decomposition pathways. The AM grassland showed relatively more plant feeding nematodes, driving soil mineralization pathways. Among the three management practices, crop cultivation had the greatest impact on nematode community structure and the soil environment, especially in relatively sensitive AM grasslands. In fact, AM soil environments responded most dramatically to cultivation, with nematode abundance, soil quality, and food web complexity increasing. However, soil ecosystem stability, food web reliance, and food web response to resources decreased in cultivated AM soils. Results indicate that unique environmental characteristics in the Qinghai-Tibet plateau drive substantially different AM grassland nematode community structure and soil conditions compared to TS or MS grasslands. As anthropogenic pressures on these ecosystems mount, it is critical to understand how different management practices influence grassland nematode communities, with cascading effects through soil environments.

Global patterns and controls of soil nematode responses to nitrogen enrichment: A meta-analysis

Nematodes are important components of soil food webs and have important ecosystem functions. However, the responses of soil nematode communities to nitrogen (N) deposition have not been well assessed over large spatial scales. Here, we conducted a global-scale meta-analysis of the effects of N-addition regimes (N form, N addition approach, and N addition rate) and environmental factors (ecosystem type, soil depth, climate, and soil property) on the responses of soil nematodes to N addition. The results showed that N addition significantly increased the relative abundance of bacterial-feeding nematodes (23.54%), but decreased the relative abundance of plant-feeding nematodes (−20.24%) and omnivorous-predatory nematodes (−22.28%). Nitrogen addition, however, did not significantly affect total nematode abundance or the relative abundance of fungal-feeding nematodes. Understory N addition usually had larger effects on nematode abundance than canopy N addition. The responses to N addition increased with N addition rate in the case of bacterial-feeding nematode abundance, but decreased with N addition rate in the case of plant-feeding nematode and fungal-feeding nematode abundances. Nematode abundance in grasslands were more responsive to N addition than in forests or croplands, and the responses were affected by soil depth. The response ratios of bacterial-feeding nematodes to N addition decreased with increases in mean annual temperature and mean annual precipitation, while the response ratios of plant-feeding nematodes showed the opposite trend. Soil pH and organic carbon did not affect the response ratios of nematode parameters to N addition except plant parasite index. In summary, the responses of soil nematodes to N addition on a global scale were found to be affected by both N-addition regimes and environmental factors. We suggest that our understanding of how N deposition affects soil nematodes will be increased by additional studies of canopy N addition and of tropical ecosystems.

Agriculture causes homogenization of plant‐feeding nematode communities at the regional scale

Abstract An emerging research line in conservation ecology addresses how environmental change drivers may cause the biotic homogenization of ecological communities by shifts in species diversity and community composition. While the drivers have been explored in unmanaged ecosystems and managed agricultural systems, this issue has received limited attention in regard to a key soil bioindicator organisms, soil nematodes. In this study, we evaluated the effect of land‐use change and intensification on the diversity of plant‐feeding nematodes (PFN) though taxonomic and functional measures of alpha and beta diversity. We selected olive tree farms in southern Spain as the study system, given the wide distribution of wild forms in unmanaged systems and cultivated forms in agricultural systems, thus providing the opportunity to assess the effects of land‐use intensity. Notably, our study revealed that the conversion from natural to agricultural systems and even moderate increases in land‐use intensity caused a significant biotic homogenization by enhancing the functional similarities of PFN communities. Our study emphasizes the key role of body size in structuring nematode communities in response to land‐use type and intensity. Synthesis and applications. The importance of soil nematodes in soil processes is well known. We show that land‐use intensification reduces soil nematode diversity. Our study has important implications for the development of management strategies that foster soil biodiversity conservation such as no or minimal tillage and logging, vegetative covers and the maintenance of natural habitat.

Quantification of the global impact of agricultural practices on soil nematodes: A meta-analysis

Agricultural practices significantly affect soil biodiversity and functions, altering biogeochemical cycles and potentially compromising food production. Increased employment of sustainable agricultural practices is of growing policy concern and requires a better understanding and quantification of how agriculture affects soil functioning. We conducted a worldwide meta-analysis by computing 4855 effect sizes from 103 publications to quantify the effect of agricultural practices on soil nematodes, known to be key biological indicators of soil health. Our meta-analysis summarized the effects of tillage, pesticides use, fertilization, manipulation of above-ground plant including cover crop, rotation and agricultural system shift (the conversion from the conventional to conservation or organic agriculture systems). We quantified how each agricultural practice alters nematode indices of ecological relevance including the absolute abundance of trophic groups, the taxonomic richness and diversity and the food web structure based on functional guilds. At the global level, organo-mineral fertilization, conservation system, cover crop and nematicides exhibited the greatest effect sizes (averaged all nematode indices) while herbicides, plant association, mineral fertilization and tillage had the lowest ones. At the level of trophic groups, the agricultural practices had varying impacts, e.g. crop rotation mainly reduced the abundance of the plant-feeding nematodes (−47%), cover crop mainly increased the abundance of omnivore-predators (+80%) while organic fertilization predominately promoted bacterial (+113%) and fungal feeders (+141%). Crop rotation reduced the absolute abundance of plant feeders by 47% when the rotation is longer than 2 years. At the community level, chemical inputs, monoculture and pesticide application reduced nematode abundance, the food web structure and favoured copiotrophic nematode communities. Biocides and nematicides reduced total abundance, Shannon diversity and the food web complexity of soil nematode (structure index). Using meta-regressions, our meta-analysis revealed that the effect of agricultural practices depends on the time since the last agricultural intervention (e.g. input of fertilizers, pesticide application) and on how long a practice has been adopted. This study will be a useful aid for decision maker to better manage soil nematode community and to identify gaps in current available literature. In providing the direction and magnitude of soil nematode responses to agricultural practices, the effect size produced by this study are critical in facilitating worldwide modelling of soil biodiversity under global change scenarios.

Increasing plant diversity promotes ecosystem functions in rainfed rice based short rotations in Malagasy highlands

Plant diversification is one of the main ways to ecologically intensify agroecosystems to improve their sustainability and resilience. Rotations and/or a mixture of crops can mitigate pest and weed infestation, reduce diseases, and improve soil fertility and crop productivity. However, rainfed rice yields in the Malagasy highlands remain low despite the frequent use of cropping systems including crop rotations and mixtures. In this study, we compared three rainfed rice based short rotations with rainfed rice monocropping to quantify the benefits of plant diversification on different ecosystem functions such as weed and nematode control, soil fertility, soil macrofauna abundance and diversity, and rice yield over four cropping seasons. The three rotations were based on rice in rotation with one legume, groundnut (RG), a cereal-legume mixture, sorghum and cowpea (RSC), or a mixture of legumes, velvet bean and crotalaria (RVC). Rice growth, N content and yield, soil N content, weed biomass, nematofauna and macrofauna were assessed and a profitability analysis was performed at rotation scale. The legume mixture had a significant and positive effect on rice growth, N content and yield, soil N content, and weed and nematode control due to high biomass production in the cropping cycle including legume mixture, by limiting weed growth and leaving a large quantity of N-rich residues to enrich the soil for the following rice crop. The nematicide properties of the legume mixture may reduce the infestation of plant-feeding nematodes. The RG and RSC rotations produced intermediate results. While rice yields were higher in these rotations than when rainfed rice was grown alone, weed biomass remained high due to minimal competition with weeds during the crop rotation cycle especially with groundnut. For RSC, nematode control was limited as both sorghum and cowpea are host plants for nematodes. Despite a year with no crop income with the RVC rotation, profitability was higher mainly due to the increased rice yield and reduced field management costs. The choice of species is thus crucial to optimise ecosystem functions adapted to farmers’ context and objectives.

Effects of plant species diversity on nematode community composition and diversity in a long-term biodiversity experiment

Diversity loss has been shown to change the soil community; however, little is known about long-term consequences and underlying mechanisms. Here, we investigated how nematode communities are affected by plant species richness and whether this is driven by resource quantity or quality in 15-year-old plant communities of a long-term grassland biodiversity experiment. We extracted nematodes from 93 experimental plots differing in plant species richness, and measured above- and belowground plant biomass production and soil organic carbon concentrations (Corg) as proxies for resource quantity, as well as C/Nleaf ratio and specific root length (SRL) as proxies for resource quality. We found that nematode community composition and diversity significantly differed among plant species richness levels. This was mostly due to positive plant diversity effects on the abundance and genus richness of bacterial-feeding, omnivorous, and predatory nematodes, which benefited from higher shoot mass and soil Corg in species-rich plant communities, suggesting control via resource quantity. In contrast, plant-feeding nematodes were negatively influenced by shoot mass, probably due to higher top–down control by predators, and were positively related to SRL and C/Nleaf, indicating control via resource quality. The decrease of the grazing pressure ratio (plant feeders per root mass) with plant species richness indicated a higher accumulation of plant-feeding nematodes in species-poor plant communities. Our results, therefore, support the hypothesis that soil-borne pathogens accumulate in low-diversity communities over time, while soil mutualists (bacterial-feeding, omnivorous, predatory nematodes) increase in abundance and richness in high-diversity plant communities, which may contribute to the widely-observed positive plant diversity–productivity relationship.

The effects of plant resource inputs on the energy flux of soil nematodes are affected by climate and plant resource type

The relative abundance of different components of the soil food web can vary tremendously in response to plant resource inputs. However, little is known about the mechanisms that plant resource regulates the energy fluxes and soil community composition. Here, we experimentally reduced litter and root inputs for two years in China at low-, mid-, and high-latitude forests to explore the effects of plant-derived resource inputs on the nematode energy flux and community composition. Litter reduction at high and mid latitudes and root removal at low latitudes reduced nematode richness but did not alter nematode abundance. Besides, litter reduction reduced energy fluxes of bacterial-feeding nematodes at mid latitudes and energy fluxes of plant-feeding, bacterial-feeding and omnivorous-predatory nematodes at low latitudes, thus reducing the energy fluxes of total nematodes in mid- and low-latitude forests. By contrast, root removal reduced energy fluxes and relative energy flux of plant-feeding nematodes in high- and low-latitude forests. In most cases, nematode diversity in different trophic groups increased with increasing energy flux to nematodes. Taken together, our results suggest that the effects of plant resource inputs on nematode energy flux are affected by climate and plant resource type, which improves our understanding of plant-soil interactions.

The Impact of Root-Derived Resources on Forest Soil Invertebrates Depends on Body Size and Trophic Position

Forest soil food webs have been assumed to be fueled substantially by root-derived resources. However, until today the flux of root-derived resources into soil animals has been investigated virtually exclusively using isotope labeling experiments, whereas studies on the consequences of disrupting the flux of root-derived resources into the soil animal food web are scarce. We here investigated the importance of root-derived resources for a wide range of soil animals by interrupting the resource flux into the soil of different forest types in Central Europe using a trenching experiment. We recorded the abundance of soil animal taxa varying in body size (micro-, meso-, and macrofauna) 1 and 3 years after root trenching, and quantified changes in biomass, species composition, and trophic shift using stable isotopes and NLFA analysis. Among the microfauna groups studied (trophic groups of Nematoda) only the abundance of plant feeding nematodes showed a trend in being decreased by -58% due to root trenching. Major soil mesofauna groups, including Collembola and Oribatida, suffered to a similar extent from root trenching with their abundance and biomass being reduced by about 30–40%. The soil macrofauna groups studied (Diplopoda, Isopoda, Chilopoda, Araneae, Coleoptera) generally were only little affected by root trenching suggesting that they rely less on root-derived resources than micro- and in particular mesofauna. Notably, the community structure of micro-, meso-, and macrofauna was not affected by root trenching. Further, we observed trophic shifts only in 2 out of 10 investigated species with the shifts generally being only minor. The results indicate that soil animal communities are markedly resilient to deprivation of root-derived resources suggesting that links to root-derived resources are non-specific. However, this resilience appears to vary with body size, with mesofauna including both decomposers as well as predators being more sensitive to the deprivation of root-derived resources than microfauna (except for root feeders) and macrofauna. Overall, this suggests that body size constrains the channeling of energy through soil food webs, with root-derived resources in temperate forests being channeled predominantly via soil taxa of intermediate size, i.e., mesofauna.

Diversity and population distribution of nematodes associated with honeybush (Cyclopia spp.) and rooibos (Aspalathus linearis) in the Western Cape province of South Africa

Nematodes are important soil organisms that constitute a key component of the soil ecosystem. A plant-parasitic survey was conducted to identify the diversity of nematodes associated with two endemic tea plants, honeybush (Cyclopia spp.) and rooibos (Aspalathus linearis) in the Western Cape province of South Africa. A total of 20 farmlands were surveyed and soil samples were collected from the rhizosphere of plants, for nematode isolation and identification based on morphological characters. Confirmation of the species of plant-parasitic nematodes was done using molecular-based tools. Nematodes were classified into various feeding groups based on their colonizer-persister (c-p) values. Plant-feeding nematodes identified from the honeybush tea plants include; Criconema mutabile, Meloidogyne hapla, M. javanica, and Xiphinema oxycaudatum, while Hoplolaimus sp., Neodolichorhynchus estherae and Pratylechus bolivianus were pathogenic on the rooibos monocultures. Bacterial and fungal feeders (Cephalobidae and Rhabditidae) were also abundant and frequently encountered in all samples. The study provides information on the diversity of nematodes associated with the indigenous herbal tea plants of South Africa.