Soil nematode community structure on the northern slope of Changbai Mountain, Northeast China

Soil nematode communities were investigated in the Changbai Mountain in Broad-leaved Korean Pine forest, Korean Pine and spruce-fix mixed forest, Dark Coniferous forest, Erman＇s birch forest and Alpine tundra along different altitude gradients from 762 m to 2 200 m a.s.l. Soil animal samples were collected from the litter layer and the soil depth of 0-5 cm, 5-10 cm and 10-20 cm at each site in the spring of 2001 and 2002. In total 27 nematode families and 60 genera were observed. The dominant genera were Plectus Bastian and Tylenchus Bastian and most of them live in litter layer. The total number of soil nematode was significantly correlated with soil moisture （r=0.357; p〈0.01）. Nematodes were classified in bacterivores, fungivores, plant parasites, omnivores-predators, and omnivores according to known feeding habitats or stoma and esophageal morphology. Species richness of fungivorous nematode was higher than others in different vegetation communities and soil depths. The total number of soil nematode and trophic groups varied significantly （o〈0.05） in response to different soil depths. The fungivore/bacterivore ratio （F/B） and the ratio of （fungivores ＋ bacterivores）/plant-parasites （WI） also changed significantly （p〈0.05） in different soil depths. In conclusion, soil moisture is proved to be one of the most important variables affecting nematode density and trophic composition, and the altitude gradient does not significantly affect the ecological indices of soil nematode such as trophic diversity （TD） and the Shannon index （H＇）.

Precipitation regulated soil nematode community and footprint in cropland ecosystems

●Nematode abundance and footprint show unimodal patterns with precipitation levels.●MAP governed nematode diversity along the precipitation gradient of agroecosystem.●Soil pH determined nematode abundance and footprint in low precipitation levels.Precipitation plays a crucial role in global biodiversity change across terrestrial ecosystems.Precipitation is proven to affect soil organism diversity in natural ecosystems.However,how precipitation change affects the function of the soil nematode community remains unclear in cropland ecosystems.Here,we tested soil nematode communities from different precipitation sites(300 mm to 900 mm)of the agricultural ecosystem.The abundance of total nematodes,fungivores,and plant parasites,together with the footprint of fungivores was significantly affected by mean annual precipitation(MAP)in cropland ecosystem.Plant parasites diversity and footprint showed negative relationships with MAP.The random forest suggested plant parasite footprint was the most responsive to MAP.The structural equation model revealed that MAP affected nematode abundance and footprint indirectly via soil pH;nematode diversity was affected by MAP directly.We conclude that precipitation could act as the main selection stress for nematode diversity among the large gradient of agricultural ecosystems.However,the soil pH may act as a stress factor in determining nematode community and carbon flow in the soil food web.Our study emphasized that using nematode value by trophic group would provide a deep understanding of nematode response to precipitation in cropland ecosystems.

Considerable impacts of litter inputs on soil nematode community composition in a young Acacia crassicapa plantation

Aboveground litter inputs and root exudates provide basal resources for soil communities,however,their relative contributions to soil food web are still not well understood.Here,we conducted a field manipulative experiment to differentiate the effects of litter inputs and living root on nematode community composition of surface and subsoils in a young Acacia crassicapa plantation in southern China.Our results showed that both litter addition and root presence significantly enhanced soil nematode abundance by 17.3%and 35.3%,respectively.Litter addition altered nematode trophic group composition,decreased fungivore to bacterivore ratio,and enhanced maturity index and structure index,which led to a bacterial-based energy channel and a more complex food web structure.However,root presence had a limited impact on the nematode community composition and ecological indices.Despite nematodes surface assembly,soil depth did not affect nematode trophic group composition or ecological index.Our findings highlight the importance of litter inputs in shaping soil nematode community structure and regulating soil energy channel.

Diversity and Dynamics of Soil Free-Living Nematode Populations in a Mediterranean Agroecosystem

To determine the effect of agricultural management on the dynamics and functional diversity of soil nematode communities in a carrot field at Kibbutz Ramat Hakovesh, Israel, soil samples from 0-10 cm and 10-20 cm depths were collected during the growing season of carrot. Indices were used to compare and assess the response of soil free-living nernatode communities to agricultural management. Eighteen nematode families and 20 genera were observed during the growing period, with Cephalobus, Rhabditidae, Aphelenchus, Tylenchus, and Dorylaimus being the dominant genera/families. During the planting, mid-season and post-harvest periods the total number of nematodes at both depths was significantly lower (P < 0.01) in the carrot treatment than in the control plots, while during the harvest period at both depths total nematodes and bacterivores were significantly higher in the treatment plots (P < 0.01). The values of the maturity index (MI) at both depths were found to be significantly lower in the treatment plots than in the control plots during the pre-planting period (P < 0.05). Overall, WI, MI and PPI were found to be more sensitive indicators than other ecological indices for assessing the response of nematode communities to agricultural management in a Mediterranean agroecosystem

Effect of free-air CO_2 enrichment on nematode communities in a Chinese farmland ecosystem

At a rice wheat rotational free air CO 2 enrichment(FACE) platform, the effect of elevated atmospheric CO 2 on soil nematode communities in a farmland ecosystem was studied. Wheat plots were exposed to elevated atmospheric CO 2(ambient 370 μl/L + 200 μl/L). 32 families and 40 genera of nematode were observed in soil suspensions during the study period. Under FACE treatment, the numbers of total nematodes, bacterivores and fungivores exhibited an increasing trend. Because of the seasonal variation of soil temperature and moisture, the effect of elevated atmospheric CO 2 on soil nematodes was only observed under favorable conditions. The response of nematode communities to elevated atmospheric CO 2 may indicate the change of soil food web.

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.

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.

Soil Biota in the Arava Valley of Negev Desert,Israel

Soil microorganism biomass and respiration and the soil nematode community were observed in the hypersaline desert valley that is found between the Dead Sea and the Red Sea. The lowest point of the valley is approximately 400 m below sea level, and is the lowest point on earth. Soil samples (n = 72) were collected from the 0-10 and 10-20 cm soil layers at different altitudes (from -400 to +100 m) in the open spaces between plants during one of the most extreme xeric periods. Both soil microbial respiration and microbial biomass were found to be negatively dependent on soil moisture (SM) and organic matter (OM), and positively dependent on pH values. The physical-chemical characteristics of this hypersaline area were extremely unfavorable for the soil nematode communities, and the nematodes were entirely absent in the open area below sea level. The bacterivores were found to be the most resistant nematodes in this hyperarid region, with the Wilsonema being the most widespread genus. We suggest that nitrogen availability may play a crucial role in the below-ground soil interaction in this region, with bacterivore nematodes as indicators of nitrogen availability.

Partial organic substitution weakens the negative effect of chemical fertilizer on soil micro-food webs

Soil biotic communities play vital roles in enhancing soil nutrient cycling and soil fertility.Long-term excessive nitrogen(N)application is disadvantageous to the stability of soil food webs and affects arable soil health and sustainable utilization.Proper organic substitution is essential to improve soil health and alleviate the disadvantages of excessive chemical fertilization.However,the biological effects of various organic amendments on soil micro-food webs are poorly understood.In order to explore the effects of various organic amendments including stover,biochar and manure on soil micro-food webs(microbial and nematode communities),a field plot experiment with maize having five treatments viz.,100%urea(100%N),70%urea(70%N),70%urea plus stover(Stover),70%urea plus cattle manure(Manure)and 70%urea plus biochar(Biochar)was conducted.Manure treatment increased the carbon(C)to N use efficiency of soil microbes,which contributed to the retention of soil C,while Biochar treatment elevated soil organic C(SOC)and soil p H.Additionally,Biochar treatment mitigated the negative effects of soil acidification on the soil micro-food web and reduced the abundance of plant parasites.Overall,the biological effect of organic amendments was distinguished from chemical fertilization(100%N and 70%N)through principal co-ordinates analysis.Negative relationships among soil properties,microbial and nematode biomass in the 100%N treatment were diminished in treatments where chemical fertilizer was reduced.The bottom-up effects on soil food webs were observed in organic substitution treatments.In conclusion,organic amendments improved soil fertility by regulating soil microbial and nematode communities in the cropland ecosystem,alleviated the negative effects of chemical fertilizer on the micro-food webs and controlled the trophic cascades among soil biota.

Soil Nematode Response to Biochar Addition in a Chinese Wheat Field

While studies have focused on the use of biochar as soil amendment, little attention has been paid to its effect on soil fauna. The biochar was produced from slow pyrolysis of wheat straw in the present study. Four treatments, no addition (CK) and three rates of biochar addition at 2 400 (B1), 12 000 (B5) and 48 000 kg ha-1 (B20), were investigated to assess the effect of biochar addition to soil on nematode abundance and diversity in a microcosm trial in China. The B5 and B20 application significantly increased the total organic carbon and the C/N ratio. No significant difference in total nematode abundance was found among the treatments. The biochar addition to the soil significantly increased the abundance of fungivores, and decreased that of plant parasites. The diversity of soil nematodes was significantly increased by B1 compared to CK. Nematode trophic groups were more effectively indicative to biochar addition than total abundance.

Responses of Soil Nematode Abundance and Diversity to Long-Term Crop Rotations in Tropical China

A field experiment was carried out from 2003 to 2013 in the Wanzhong Farm of the Hainan Island, China, to determine the effects of two long-term banana rotations on the abundance and trophic groups of soil nematode communities in the island. The experiment was set out as a randomized complete block design with three replications of three treatments： banana-pineapple rotation （AB）, banana-papaya rotation （BB） and banana monoculture （CK） in a conventional tillage system. Soil samples were taken at depths of 0-10, 10-20 and 20-30 cm, and nematodes were extracted by a modified cotton-wool filter method and identified to the genus level. Nematode ecological indices of Shannon-Weaver diversity （Ht）, dominance index （A）, maturity index （MI）, plant parasite index （PPI）, structure index （SI）, enrichment index （EI）, and channel index （CI） were calculated. A total of 28 nematode genera with relative abundance over 0.1% were identified, among which Tylenchus and Paratylenchus in the AB, Thonus in the BB, Tylenchus and Helicotylenchus in the CK were the dominant genera. The rotation soils favored bacterivores, fungivores and omnivores-predators with high colonizer-persister （c-p） values. Soil food web in the rotation systems was highly structured, mature and enriched as indicated by SI, MI and EI values, respectively. Higher abundance of bacterivores and lower values of CI suggested that the soil food web was dominated by a bacterial decomposition pathway in rotation soils. Nematode diversity was much higher after a decade of rotation. Soil depth had significant effects on the abundance of soil nematodes, but only on two nematode ecological indices （λ and MI）.

Effect of grassland degradation on soil quality and soil biotic community in a semi-arid temperate steppe

Grasslands provide a number of ecosystem services for human society.Degradation of grasslands results in the loss of biodiversity and leads to the deterioration of ecosystem functions.In order to accurately assess the influence of grassland degradation on belowground ecosystems,we conducted experiments on a temperate steppe with different levels of degradation and investigated the influence of degradation on soil quality and soil biotic communities.Our results showed that grassland degradation significantly decreased soil quality,with lower values of soil quality index(SQI)observed in the degraded grassland than the meadow steppe and the grassland from the forest-steppe ecotone.Changes in the SQI along the grassland degradation gradient were positively correlated with soil carbon stock and the aboveground biomass,and negatively correlated with the root shoot ratio.Nematode trophic diversity and the ratio of fungal to bacterial PLFA were lower in the degraded grassland than the grassland from the forest-steppe ecotone.The dissimilarities in soil microbial and nematode community composition increased with the changes in soil quality index.Our results indicate that soil quality index based on the minimum data sets could effectively assess the influence of grassland degradation on soil biodiversity and ecosystem function.In order to effectively restore degraded grasslands,the key contributors to the soil quality,such as soil carbon,should be taken on priority basis for revitalizing the soil biodiversity and ecosystem function.

Organic amendment effects on nematode distribution within aggregate fractions in agricultural soils

To evaluate the effect of organic amendments on soil nematode community composition and diversity within aggregate fractions,a study was initiated in agricultural soils with four-year organic amendments.Soil samples were collected from the plow layer(0-20 cm)under three cornfield management scenarios:1)conventional cropping(CK,corn straw removal and no organic manure application);2)straw retention(SR,incorporation of chopped corn stalk);and 3)manure application(MA,chicken manure input).The soil samples were fractionated into four aggregate sizes,i.e.,>2 mm(large macroaggregates),1-2 mm(macroaggregates),0.25-1 mm(small macroaggregates),and<0.25 mm(microaggregates,silt and clay fractions).The composition and diversity of soil nematode communities were determined within each aggregate fraction.The results showed that both SR and MA treatments significantly increased the percentage of macroaggregates(>1 mm)and only MA treatment strongly increased the mean weight diameter compared to the CK(P<0.05).The abundance of total nematodes and four trophic groups were affected significantly by the aggregate fractions and their higher abundance occurred in the larger aggregates.The effects of aggregate size on most nematode genera were significant.Bacterivores in the small macroaggregates and microaggregates,and fungivores in the large macroaggregates were significantly different among treatments.The percentage of bacterivores increased after the application of organic materials,while that of fungivores decreased.It can be concluded that organic management significantly affects soil aggregation and soil characteristics within aggregates,and the aggregate size subsequently influences the distribution of nematode communities.

Distributional patterns of soil nematodes in relation to environmental variables in forest ecosystems

Understanding biodiversity and biogeographic distribution of soil fauna is an important topic in ecology.While nematode communities have been compared among ecosystems,knowledge remains limited about how environmental factors and nematode distributions are linked at different spatial scales.Hare,we employed high-throughput sequencing to compare nematode communities in tropical(Xishuangbanna),subtropical(Ailaoshan),and cold temperate spruce-fir(Lijiang)forest ecosystems with identical spatial sampling.Relationships between nematode communities and environmental factors were analyzed using redundancy analysis(RDA).Our results showed that nematode richness and diversity peaked in Xishuangbanna;however,no significant differences were observed in other two forest ecosystems.Bacterial feeders and Omnivores/Camivores(Om&Ca)had the lowest relative abundance,but the highest diversity,in Xishuangbanna,with the opposite pattem being detected for fungal and plant feeders.Our data also demonstrated that,for forest ecosystems,climate factors drive nematode communities distributions at the regional scale,while terrain and soil characteristics(including pH and nutrients)drive nematode communities distributions at local scales.This study improves our current understanding of key factors(environmental parameters)responsible for the biogeographical distribution of forest nematode communities at different spatial scales.

Seasonal Effect of Geomorphological Chronosequence Features on Soil Biota Dynamics

Numerous studies have been devoted to the physical-chemical weathering processes leading to the creation of unique soil formations having their own history that induce soil-biotic diversity.However,the extent to which unique geomorphic formations influence soil biotic seasonal variation is not clear.Our aim was to define seasonal variations of soil biota in soils of different-aged terraces of the Makhtesh Ramon anticline erosional cirque in southern Israel.The strong effect of Makhtesh Ramon (Ramon crater) erosional fluvial terrace age initiated by climatic changes during the Late Pleistocene- Early Holocene period on seasonal variations in both soil properties and the abundance and composition of soil biota were demonstrated.However,age dependence was not constant and values for observed soil properties and microbial activity were negligible between younger and older terraces for certain seasons,while free-living nematodes along with bacterial-feeding group were strongly dependent on the geomorphic features of the ages throughout the study period.