Effects of Wetland Utilization Change on Spatial Distribution of Soil Nematodes in Heihe River Basin, Northwest China

The first account of the effects of wetland reclamation on soil nematode assemblages were provided, three sites in Heihe River Basin of Northwest China, that is grass wetland(GW), Tamarix chinensis wetland(TW) and crop wetland(CW) treatments, were compared. Results showed that the majority of soil nematodes were presented in the 0–20 cm soil layers in CW treatments, followed by in the 20–40 cm and 40–60 cm layers in GW treatments. Plant-feeding nametodes were the most abundant trophic groups in each treatment, where GW(91.0%) > TW(88.1%) > CW(53.5%). Generic richness(GR) was lower in the TW(16) than that in GW(23) and CW(25). The combination of enrichment index(EI) and structure index(SI) showed that the soil food web in GW was more structured, and those in TW was stressed, while the enrichment soil food web was presented in the CW treatment. Several ecological indices which reflected soil community structure, diversity, Shannon-Weaver diversity(H′), Evenness(J′), Richness(GR) and modified maturity index(MMI) were found to be effective for assessing the response of soil namatode communities to soil of saline wetland reclamation. Furthermore, saline wetland reclamation also exerted great influence on the soil physical and chemical properties(p H, Electric conductivity(EC), Total organic carbon(TOC), Total nitrogen(Total-N) and Nitrate Nitrogen(N-NO3–)). These results indicated that the wetland reclamation had significantly effects on soil nematode community structure and soil properties in this study.

Effect of land use on soil nematode community composition and co-occurrence network relationship

Land use influences soil biota community composition and diversity,and then belowground ecosystem processes and functions.To characterize the effect of land use on soil biota,soil nematode communities in crop land,forest land and fallow land were investigated in six regions of northern China.Generic richness,diversity,abundance and biomass of soil nematodes was the lowest in crop land.The richness and diversity of soil nematodes were 28.8and 15.1%higher in fallow land than in crop land,respectively.No significant differences in soil nematode indices were found between forest land and fallow land,but their network keystone genera composition was different.Among the keystone genera,50%of forest land genera were omnivores-predators and 36%of fallow land genera were bacterivores.The proportion of fungivores in forest land was 20.8%lower than in fallow land.The network complexity and the stability were lower in crop land than forest land and fallow land.Soil pH,NH_(4)^(+)-N and NO_(3)^(–)-N were the major factors influencing the soil nematode community in crop land while soil organic carbon and moisture were the major factors in forest land.Soil nematode communities in crop land influenced by artificial management practices were more dependent on the soil environment than communities in forest land and fallow land.Land use induced soil environment variation and altered network relationships by influencing trophic group proportions among keystone nematode genera.

A review of soil nematodes as biological indicators for the assessment of soil health

Healthy soils are essential for sustainableagricultural development and soil health requires carefulassessment with increasing societal concern over envir-onmentally friendly agricultural development. Soil healthis the capacity of soil to function within ecologicalboundaries to sustain productivity, maintain environmentalquality, and promote plant and animal health. Physical,chemical and biological indicators are used to evaluate soilhealth;the biological indicators include microbes, proto-zoa and metazoa. Nematodes are the most abundantmetazoa and they vary in their sensitivity to pollutants andenvironmental disturbance. Soil nematode communitiesare useful biological indicators of soil health, withcommunity characteristics such as abundance, diversity,community structure and metabolic footprint all closelycorrelated with the soil environment. The community size,complexity and structure reflect the condition of the soil.Both free-living and plant parasitic nematodes are effec-tive ecological indicators, contributing to nutrient cyclingand having important roles as primary, secondary andtertiary consumers in food webs. Tillage inversion,cropping patterns and nutrient management may havestrong effects on soil nematodes, with changes in soilnematode communities reflecting soil disturbance. Somefree-living nematodes serve as biological models to testsoil condition in the laboratory and because of theseadvantages soil nematodes are increasingly being used asbiological indicators of soil health.

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.

Effect of heavy metals on soil nematode communities in the vicinity of a metallurgical factory

The influence of Cu and Zn on soil nematode communities was examined along a pollution gradient with increasing distance from a metallurgical factory. Total and available heavy metal contents were used to study the effects of heavy metals on nematode abundance, trophic groups and ecological indices. The results demonstrated significant correlations between the number of total nematodes, bacterivores, plant-parasites and the total and available heavy metals. Bacterivores and plant-parasites were the dominant trophic groups. Significant differences in different sampling sites were found only in the number of bacterivores（P〈0.01）. The Shannon-Weaver diversity index（W）, trophic diversity index（TD）, evenness index（J＇） and dominance index（λ） were found to be sensitive to soil pH and C/N ratios. Significant correlations were found between the total nematodes （TNEM）, some genera （A crobeloides, Aphelenchoides, Cephalobus, Ditylenchus, Mesorhabditis, Tetylenchus and Tylenchus） and distance from the factory.

Response of Nematodes in a Hapli-Udic Argosol to Urea Amended with Urease and Nitrification Inhibitors

Effects of urea amended with urease and nitrification inhibitors on soil nematode communities were studied in a Hapli- Udic Argosol （Cambisol, FAO） in Liaoning Province of Northeast China. A completely random design with four treatments, i.e., conventional urea （CU）, slow-release urea amended with a liquid urease inhibitor （SRU1）, SRU1 ＋nitrification inhibitor dicyandiamide （SRU2）, and SRU1 ＋ nitrification inhibitor 3,5-dimethylpyrazole （SRU3） and four replicates were applied. Thirty-nine genera of nematodes were identified, with Cephalobus and Aphelenchus being dominant; and in all treatments, the dominant trophic group was bacterivores. In addition, during the growth period of spring wheat （Triticum aestivum L.）, soil urease activity was lower in SRUs than in CU. The numbers of total nematodes and bacterivores at wheat heading and ripening stages, and omnivores-predators at ripening stage were higher in SUR3 than in CU, SRU1 and SRU2 （P 〈 0.05）.

Impacts of Nighttime Warming on the Soil Nematode Community in a Winter Wheat Field of Yangtze Delta Plain, China

Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland （e.g., winter wheat field） have not been well documented. Therefore, a field experiment with free air temperature increase （FATI） was conducted to investigate the responses of the soil nematode community to nighttime warming in a winter wheat field of Yangtze Delta Plain, China, during 2007 to 2009. Nighttime warming （NW） by 1.8~C at 5-cm soil depth had no significant impact on the total nematode abundance compared to un-warmed control （CK）. However, NW significantly affected the nematode community structure. Warming favored the bacterivores and fungivores, such as Acrobeles, Monhystera, Rhabditis, and Rhabdontolaimus in bacterivores, and Filenchus in fungivores, while the plant-parasites were hindered, such as Helicotylenchus and Psilenchus. Interestingly, the carnivores/ omnivores remained almost unchanged. Hence, the abundances ofbacterivores and fungivores were significantly higher under NW than those under CK. Similarly, the abundances of plant-parasites were significantly lower under NW than under CK. Furthermore, Wasilewska index of the nematode community was significantly higher under NW than those under CK, indicating beneficial effect to the plant in the soil. Our results suggest that nighttime warming may improve soil fertility and decrease soil- borne diseases in winter wheat field through affecting the soil nematode community. It is also indicated that nighttime warming may promote the sustainability of the nematode community by altering genera-specific habitat suitability for soil biota.

Effect of Cultivation on Spatial Distribution of Nematode Trophic Groups in Black Soil

Geostatistics combined with GIS was applied to assess the spatial distribution of nematode trophic groups following two contrasting soil uses in the black soil region of Northeast China. Two plots, one with fallow for 12 years and the other cultivated, were marked on regular square grids with 2-m spacing. Soil samples were collected from each sampling point, nematodes were extracted from these samples and classified into four trophic groups: bacterivores, fungivores, plant parasites, and omnivores/predators. The numbers of total nematodes and trophic groups analyzed had normal distributions on both fallow and cultivated plots. The absolute abundances of total nematodes and trophic groups were observed to be much more homogeneous on cultivated plot than on fallow one. Geostatistical analysis showed that the densities of total nematodes and trophic groups on both fallow and cultivated plots exhibited spatial dependence at the sampled scale and their experimental semivariograms were adjusted to a spherical or exponential model, except those of bacterivores and fungivores on cultivated plot. The spatial distribution of nematode trophic groups was found to be different for the two land uses, indicating that cultivation changed the native condition for soil nematode activities.

Effects of heavy metal pollution of highway origin on soil nematode guilds in North Shenyang, China

Soil samples were collected with distance at 5, 20, 40, 80, 160, and 320 m from the Shen-Ha （Shenyang-Harbin） Highway, Northeast China, to investigate the effect of heavy metals of highway origin on soil nematode guilds. The contents of soil Pb, Cu, Zn, and the nematode community structure were analyzed. The results showed that the contents of total and available Pb, Ca, Zn varied significantly with the different distances from the highway. Pb was the main pollutant in the soils in the vicinity of Shen-Ha Highway. The zone from 20 to 40 m away from the highway was the most polluted area. The highest abundance of soil nematodes was found at 5 m while the lowest at 20 m away from the highway. Thirty six genera of nematodes belonging to 23 families were identified. Nematode guilds having different responses to soil heavy metals were classified into four types. Soil nematode guilds may act as a prominent indicator to heavy metal pollution of highway origin.

Salinity effects on soil organic carbon and its labile fractions,and nematode communities in irrigated farmlands in an arid region,northwestern China

The effects of salinity on soil organic carbon （SOC） and its labile fractions including microbial biomass carbon （MBC） and easily oxidation organic carbon （EOC）, basal soil respiration, and soil nematode community in the Fluvents, an oasis in an arid region of northwestern China were investigated. Five sites were selected which had a salinity gradient with different groundwater table from 1.0 m to 4.0 m. Soils were sampled at the 0~0 cm plough layer from 25 irrigated fields of five sites and electrical conductivity was measured in the saturation paste extracts （ECe）. Soils were categorized into five salinity levels： （1） non-saline, （2） very slightly saline, （3） slightly saline, （4） moderately saline, and （5） strongly saline according to the values of ECe. The results show that SOC and total nitrogen concentration, cation exchange capacity （CEC）, and the concentrations of labile organic fractions （MBC, EOC）, and basal soil respiration decreased significantly with increasing ECe. The relationships between ECe and MBC, EOC and basal soil respiration were best described by power functions. Slight and moderate salinity had no significant impact on soil nematode abundance, but excessive salt accumulation led to a marked decline in soil nematode community diversity and abundance. Soil salinity changed soil nematode trophic groups and bacterivores were the most abundant trophic groups in salt-affected soils. Further study is necessary to identify the response of soil microbial processes and nematode community dynamics to soil salinity.

Vertical Distribution of Soil Nematode Communities under Different Tillage Systems in Lower Reaches of Liaohe River

Vertical distribution of soil nematode communities under conventional tillage (CT),no-tillage (NT) and fallow field (FF) treatments in the Lower Reaches of the Liaohe River was investigated at six soil depths (0-5 cm,5-15 cm,15-30 cm,30-50 cm,50-75 cm and 75-100 cm). The results show that total nematode abundance gradually decreases with depth,and the highest number of total nematodes is observed at 0-5 cm depth under NT and FF treatments. The number of fungivores and plant parasites is significantly higher under FF and NT treatments than under CT treatment at the 0-5 cm depth. There is significant soil depth effect on the abundances of bacterivores and omnivores-predators,which exhibits a similar trend to that of total nematodes; whereas,no significant tillage effect is found. Tillage effect on soil nematode communities can be reflected by values of relative tillage response of index V. Results of index V indicate that total nematodes,bacterivores,fungivores and plant parasites are mildly inhibited,and omnivores-predators is moderately inhibited under CT treatment; while,under FF treatment total nematodes is mildly,and fungivores and plant parasites are moderately stimulated,respectively.

Effects of Different Woodland Types on Soil Properties and Soil Nematode Community Structure

Upland red soil has strong acidity and low fertility, different woodland types produce varying impacts on soil properties and nematode communities. To explore the response of soil, 2 different types of woodland were selected to investigate the changes of soil properties and nematode communities compared to wasteland. The results showed that the content of soil organic carbon and total nitrogen in chestnut forest soil were the highest, 16.41 g/kg and 0.46 g/kg respectively; while the highest contents of soil microbial biomass carbon, nitrogen and phosphorus appeared in wasteland soil, and basal respiration of wasteland soil was 28.36 mg CO_2/kg·d, significantly higher than that of the other 2 soils(p <0.05). The nematode abundance also reached the peak in wasteland soil. Three types of soil exhibited a completely different nematode community structure: the dominant trophic group in wasteland soil was herbivores,while omnivores/predators and bacterivores in forest from farmland and chestnut forest soil, respectively.The influence of different types of woodland on ecological indices of nematode communities was not consistent. Degradation trends of soil properties and nematode communities were presented in the 2woodland types compared with wasteland soil. These results are instructive for the local woodland planning.

Variation and Dynamics of Soil Nematode Communities in Greenhouses with Different Continuous Cropping Periods

Continuous cropping in greenhouses can result in root-knot nematode outbreaks resulting from imbalances in the soil nematode community.However,the changes in soil nematode communities in greenhouses with continuous crop production are unclear.We compared soil nematode communities in greenhouses after 2 years(2-yr)and 10 years(10-yr)of continuous crop production by 18S rDNA high-throughput sequencing.Compared with the 2-yr greenhouse,soil in the 10-yr greenhouse showed acidification,nutrient accumulation and salinization.Bacterial-feeding nematodes(BF)were dominant in the 2-yr greenhouse over the whole growing season,but plant-parasitic nematodes(PP)were the dominant group in the 10-yr greenhouse during the late growing season.Meloidogyne gradually became the dominant group and had a relative abundance of 70.9%(maximum)in the 10-yr greenhouse.Rhabditidae,with relative abundance ranging from 99.8%to 26.8%,was the predominant group in the 2-year greenhouse.Forβ-diversity,hierarchical clustering analysis,unweighted UniFrac principal component analysis(PCA)and principal co-ordinates analysis(PCoA)all revealed that soil nematode communities in the two types of greenhouses were significantly different.Redundancy analysis(RDA)showed that soil nematode communities in the 10-yr greenhouse were related to high soil organic material,total nitrogen,electrical conductivity and disease index of root-knot nematodes.Fisher’s exact test and Pearson’s correlation coefficients revealed that Meloidogyne contributed to themain differences in soil nematode communities between the two types of greenhouses.Population dynamics of Meloidogyne were divided into dormant phase,low-level increasing phase and exponential phase during the whole season.The soil nematode communities within the 2-yr and 10-yr greenhouses had significant variation and different dynamics.This work contributes to a deeper understanding of changes in the soil nematode community in greenhouses with different continuous cropping duration.

Advancements in assessing soil health through functional traits and energy flow analysis of soil

We examined the development of soil nematodes ecological indices from the perspective off unctionaltraits.We found that soil nematode energy flow analyses based on multiple functional traits quantify the dynamics of energy flow across multipletrophic levels to provide a more comprehensive perspective.We conducted comparative analyses of the sensitivities of NMF and energy flow to verify that the energy flow analyses are more sensitive and have greater potential to reveal soil health and ecosystem function.Future in-depth studies of functional traits and energy flow analysis can help us achieve informed soil management practices,sustainable agriculture,andhealthiersoilecosystems.nignerEauc Tess CT Nematode ecological index based on functional traits:MI El,S,BI,C1 NMF Bongen.1990 Ferrisetal,2001 Ferris,2010 energs low analysis of soil nematodes Compare thecological index(NMf)and Bacterivores(Ba)Functional traits Energy flux Fungihores(Fn)rahn Soilnematodes latitude Lindicator Plant-parasites(PP)PF Energflus Soilhealth Omnivores-predators(oP)latitude Energy flow analysis of soil nematodes:By quantifying energy fux among trophic groups Barbes et al.,2014,2018 This paper examines the development of ecological indices for soil nematodes from the perspective of functional traits.It emphasizes the increasing significance of integrating multiple functional traits to achieve a more accurate assessment of soil health.Ecological indices based on life history strategies,feeding habits,and body size provide useful tools for assessing soil health.However,these indices do not fully capture the dynamics ofenergyflow across multiple-trophic levels inthesoil foodweb,which is critical fora deeperunderstanding of the intrinsic properties of soil health.By combining functional traits such as functional group,body size,feeding preference and metabolic rate,nematode energy flow analyses provide a more comprehensive perspective.This approach establishes a direct correlation between changes in the morphology,physiology,and metabolism of soil organisms and alterations in their habitat environment.We conducted comparative analyses of the sensitivity of nematode metabolic footprints and energy flow to latitudinal variation using a nematode dataset from the northeastern black soil region in China.The findings suggest that energy flow analyses are more sensitive to latitude and have greater potential to reveal soil health and ecosystem function.Therefore,future research should prioritize the development of automated and efficient methods for analyzing nematode traits.This will enhance the application of energy flow analyses in nematode food webs and support the development of sustainable soil management and agriculturalpractices.

Effects of nitrogen and phosphorus additions on soil nematode community of soybean farmland

The nitrogen(N)and phosphorus(P)addition promotes the abundance of soybean soil nematodes.The addition of nitrogen can alleviate the suppression of phosphorus on nematodes.Phosphorus addition affects nematode abundance by ammonium nitrogen.

A single degenerated primer significantly improves COX1 barcoding performance in soil nematode community profiling

A new COX1 primer for soil nematode metabarcoding was designed,and this primer outperforms other commonly used COX1 primer pairs in species recovery and quantity of PCR products.•The lack of reference database is the main reason that led to the low species recovery in COX1 metabarcoding.•We expanded current NCBI database by adding 51 newly generated COX1 reference sequences.Microscopic nematodes play important roles in soil ecosystems and often serve as bioindicators of soil health.The identification of soil nematodes is often difficult due to their limited diagnostic characters and high phenotypic plasticity.DNA barcoding and metabarcoding techniques are promising but lack universal primers,especially for mitochondrial COX1 gene.In this study a degenerated COX1 forward primer COIFGED was developed.The primer pair(COIFGED/JB5GED)outperforms other four commonly used COX1 primer pairs in species recovery and quantity of polymerase chain reaction(PCR)products.In metabarcoding analysis,the reads obtained from the new primer pair had the highest sequencing saturation threshold and amplicon sequence variant(ASV)diversity in comparison to other COX1 as well as 18S rRNA primers.The annotation of ASVs suggested the new primer pair initially recovered 9 and 6 out of 25 genera from mock communities,respectively,outperformed other COX1 primers,but underperformed the widely used 18S NF1/18Sr2b primers(16 out of 25 genera).By supplementing the COX1 database with our reference sequences,we recovered an additional 6 mock community species bringing the tally closer to that obtained with 18S primers.In summary,our newly designed COX1 primers significantly improved species recovery and thus can be supplementary or alternative to the conventional 18S metabarcoding.

Nematode Faunal Response to Grassland Degradation in Horqin Sandy Land

The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG), degraded grassland (DG),and improved grassland (IG),in Horqin Sandy Land,Inner Mongolia,Northeast China.Soil samples were collected at depths of 0-10,10-20,and 20-30 cm.Total organic carbon (TOC) and total nitrogen (TN) exhibited positive effects on the total number of nematodes and trophic groups.Significant treatment effects were found in the total number of nematodes,plant parasites,and omnivores-predators.Measures taken in the improved grassland could improve the number of omnivore-predators,especially in the deeper soil layers.Nematode richness was lower in the DG treatment than in the IG and UG treatments.The food web structure index (SI) was significantly higher in the UG and IG treatments than in the DG treatment.A higher SI suggested a food web with more trophic linkages and relatively healthy ecosystems.

Effects of long-term straw incorporation on nematode community composition and metabolic footprint in a rice–wheat cropping system

Soil nematode communities can provide valuable information about the structure and functions of soil food webs,and are sensitive to agricultural practices,including short-term straw incorporation.However,currently,such effects under longterm straw incorporation conditions at different fertility levels are largely unknown.Thus,we conducted a 13-year ongoing experiment to evaluate the effects of long-term straw incorporation on the structure and functions of the soil food web in low and high fertility soils through analyzing its effects on nematode communities,food web indices and metabolic footprints.Four treatments were included:straw removal(–S)under non-fertilized(–NPK)or fertilized(+NPK)conditions;and straw incorporation(+S)under–NPK or+NPK conditions.Soil samples from a 0–20 cm depth layer were collected when wheat and rice were harvested.Compared with straw removal,straw incorporation increased the abundances of total nematodes,bacterivores,plant-parasites and omnivores-predators,as well the relative abundances of omnivores-predators with increases of 73.06,89.29,95.31,238.98,and 114.61%in–NPK soils and 16.23,2.23,19.01,141.38,and 90.23%in+NPK soils,respectively.Regardless of sampling times and fertilization effects,straw incorporation increased the diversity and community stability of nematodes,as indicated by the Shannon-Weaver diversity index and maturity index.Enrichment and structure index did not show significant responses to straw incorporation,but a slight increase was observed in the structure index.The analysis of nematode metabolic footprints showed that straw incorporation increased the plant-parasite footprint and structure footprint by 97.27 and 305.39%in–NPK soils and by 11.29 and 149.56%in+NPK soils,but did not significantly influence enrichment,bacterivore and fungivore footprints.In conclusion,long-term straw incorporation,particularly under a low fertility level,favored the soil nematodes and regulated the soil food web mainly via a top-down effect.

Consistent response of nematode communities to management of coniferous plantations

Background:Crop-tree thinning (CTT) is a forest management practice aiming at enhancing the growth of target trees in plantations by harvesting neighboring trees. Along with the positive effect on tree growth, thinning represents a disturbance, which likely affects belowground organisms and may feed back to stand productivity.However, the impact of CTT on the belowground food web is poorly understood. Since nematodes are species-rich and abundant belowground organisms, occupying a variety of trophic positions in soil food webs and being sensitive to disturbances, they serve as ecological indicators of ecosystem disturbance.Results:We studied the effect of CTT on the soil nematode community structure in pine (Pinus massoniana Lamb.),Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and cypress (Cupressus funebris Endl.) plantations in the Sichuan Basin three years after applying CTT. Crop-tree thinning significantly increased the abundance of soil nematodes in each of the plantations. Moreover, CTT significantly increased the relative abundance of herbivorous nematodes in each of the plantations. Furthermore, CTT increased the proportion of stress tolerators (c-p 1)and enrichment opportunists (c-p 2) and reduced the maturity, structure and enrichment indices of nematodes in Chinese fir and cypress plantations, while only subtle changes were observed in pine plantations. Interestingly,across plantations, the effects of CTT on soil nematode communities were mainly due to changes in microbial biomass nitrogen and understory vegetation diversity.Conclusions:Forest management practices resulting in more open canopies uniformly affect soil food webs by changing the quantity and quality of resources associated with increased understory cover and diversity as well as microbial food. These insights increase our understanding of the impacts of forest management on the structure and functioning of belowground communities, which may contribute to management and conservation policies for more sustainable forestry.

Effects of fertilizer and weed species richness on soil nematode community in a microcosm field experiment

Both fertilizer and plant species richness may affect the soil nematode community.However,the influence of fertilizer and weed species richness interaction is unclear.Nematode abundance and biodiversity in wheat and weed plots soil treated with nitrogen,phosphate and potassium fertilizer addition and weed species richness(0,1,2 and 4 weed levels)were investigated in a long-term microcosm experiment established in 2010 at Kaifeng,China.The results demonstrated that fertilizer treatment increased the abundance of total nematode,bacterivores,and plant parasites whereas it decreased the total genera number,the Shannon-Wiener diversity index(H'),Margalef richness index(SR),the total maturity index(∑MI),and structure index(SI),and degraded the structure of the nematode community.In contrast,weed species richness increased these ecological indices and enhanced the structure of the nematode community.Principal component analysis(PCA)indicated that the fertilizer's effect was more significant than weed species richness.Redundancy analysis(RDA)demonstrated that fertilizer affected soil nematode mainly through increasing soil available phosphorus by 4.71 times and ammonium nitrogen content by 74.03%;weed species richness increased the diversity indices of soil nematode mainly through enhancing soil moisture by 2.07%.Our results suggest weed species richness may relieve the negative effect of fertilizer on the diversity of soil nematode community.