Short-term effects of different tillage in a sustainable farming system on nematode community structure

This study investigated the effects of different tillage practices on the nematode community structure. The different tillage systems were: untilled control, conventional deep plough, two-layer plough and cultivator. Sampling was carried out in a field experiment at Wörrstadt-Rommersheim (Rhineland-Palatinate, Germany) in order to study the effects of these tillage systems in a sustainable farming system. Soil samples were taken every 3?months from June 1994 to March 1995 and divided into two depths of 0–10 and 10–20?cm in order to study the vertical distribution of nematode density and community structure. Nematode density was significantly reduced after the first tillage. The second tillage had no effect on the nematode density, whereas the nematode community structure was strongly influenced on both structural (taxonomic) and functional (trophic group, life strategy) level. After tillage, the density of plant parasitic nematodes decreased and the density and dominance of bacterivorous nematodes increased. In the tilled plots, and especially in the cultivator and the two-layer plough plot, the nematode community was dominated by bacterial feeders, whereas, in the untilled control, plant feeders were more dominant. Our results showed that the nematode Maturity Index and Plant Parasite Index are suitable for indicating immediate tillage effects on the nematode community.     

Soil nematode assemblages as bioindicators of primary succession along a 120-year-old chronosequence on the Hailuogou Glacier forefield,SW China

Successional dynamics in terrestrial ecosystems is important for interactions between aboveground and belowground subsystems. In this study, nematode communities in a Hailuogou Glacier Chronosequence from seven stages were investigated to determine whether changes in soil phosphorus (P) and nematode assemblages parallel those observed in aboveground communities, and whether the primary succession in this chronosequence has entered a retrogressive phase after 120 years of succession. The initial 40-year succession, including stages 2, 3 and 4, can be viewed as a build-up phase. Especially at stage 3, vegetation succession from grassland to forest accelerated the accumulation of plant litter and bioavailable P, paralleled with a sharp increase in nematode abundance. The mature phases covering stages 5, 6 and 7 displayed most balanced nematode communities, in which abundance, taxon richness, maturity index and structure index were at highest. However, the last stage 7 appeared to show some retrogressive characteristics, as suggested by the reduced bioavailability of P and a significant decrease in nematode densities, along with the disappearance of some rare genera of nematodes from higher trophic guilds, resulting in decreases in the nematode channel ratio, plant parasite index and enrichment index. Thus, the Hailuogou Glacier Chronosequence may enter its retrogressive phase during the next decade or century. A bacterial-based nematode energy channel dominated the chronosequence during the development; by contrast, a fungivore-based channel was activated at the early and late stages, because fungivores are better adapted to nutrient-poor environments. Our results demonstrated that different nematode guilds have contrasting responses to chronosequence stages, possibly due to their different responses to bottom-up and top-down controls. Furthermore, soil nematode communities could be used as sensitive bioindicators of soil health in glacial-retreat areas.     

Assessing the impact of cultivation and plant domestication of highbush blueberry (Vaccinium corymbosum) on soil properties and associated plant-parasitic nematode communities

We investigated the interactive effects of plant domestication and perennial cultivation on diversity and richness of plant-parasitic nematode (PPN) communities associated with highbush blueberry (Vaccinium corymbosum). Rhizospheric soil of V. corymbosum plants was sampled in coupled wild and cultivated sites within the Pinelands National Reserve. Although PPN diversity was higher in cultivated plant soil samples, richness was higher in wild plant soil samples. The most important soil properties, iron and calcium, were associated with cultivated soil and were the best predictors of genera abundance patterns. Nematodes in the genus Criconemoides were 187× more abundant in wild sites than cultivated and thus, were significant indicators of wild sites. In this study cultivation of V. corymbosum appears to benefit the PPN community but alters the community composition considerably.     

大豆胞囊线虫4号生理小种不同抗性材料根系分泌物对其抗病性的影响

为研究大豆根系分泌物与大豆对胞囊线虫4号生理小种抗性的关系,以CBL黑豆(抗)和品75-14(感)为试材,收集其不同处理的根系分泌物,测定根系分泌物对胞囊线虫4号生理小种卵孵化的影响和对二龄幼虫的趋化性,并测定了根系分泌物中氨基酸成分及含量,分析了其与大豆对胞囊线虫4号生理小种抗性之间的相关性。结果表明:CBL黑豆根系分泌物能抑制线虫卵的孵化,而品75-14根系分泌物能刺激卵的孵化。品75-14根系分泌物对二龄幼虫趋化性影响显著大于CBL黑豆。在供试材料大豆根系分泌物中共检测出17种氨基酸。无论接种与否,品75-14根系分泌物中氨基酸总量高于CBL黑豆,是CBL黑豆根系分泌物中氨基酸总量的2倍多。与不接种对照相比,接种后CBL黑豆和品75-14根系分泌物氨基酸总量都表现为增加,且品75-14增幅大于CBL黑豆,品75-14根系分泌物中氨基酸总量增加了297.29μg·g-1FW,而CBL黑豆增加了191.15μg·g-1FW。根据氨基酸增幅及变化规律,将氨基酸分为3类:第一类为苯丙氨酸,与大豆对胞囊线虫4号小种的抗性呈正相关;第二类包含3种氨基酸,分别为苏氨酸、丝氨酸和蛋氨酸,与抗性不相关;第三类包含其余13种氨基酸,与抗性呈负相关。     

8种检疫线虫传入黑龙江的风险评估

根据国际植物保护公约(InternationalPlantProtectionConvention,IPPC)的国际植物检疫措施标准11(InternationalStandardforPhytosanitaryMeasures11,2001,ISPM11)并参考欧洲和地中海植物保护组织(EuropeanandMediterraneanPlantProtectionOrganization,EPPO)有害生物风险分析风险评估指导标准(EPPOStandardPM5/3GuidelinesonPestRiskAnalysis—PestRiskAssessmentScheme),对马铃薯金线虫、马铃薯白线虫、相似穿孔线虫、鳞球茎茎线虫、甜菜胞囊线虫、水稻茎线虫、椰子红环腐线虫和松材线虫这8种检疫性线虫传入黑龙江省进行风险评估。风险评估表明,相似穿孔线虫传入黑龙江省具有高度风险,马铃薯金线虫、马铃薯白线虫、鳞球茎茎线虫、甜菜胞囊线虫、和松材线虫传入黑龙江省具有较高风险,水稻茎线虫风险较低、椰子红环腐线虫无风险。应该加强对风险较高的几种线虫的风险管理。     

中国小黑豆对大豆胞囊线虫3号生理小种的抗性遗传研究

用大豆胞囊线虫（Ｈｅｔｅｒｏｄｅｒａｇｌｙｃｉｎｅｓ）３号生理小种接种抗病品种小粒黑豆、连毛会黑豆、磨石黑豆与感病品种铁丰２４号、铁丰１８号、开育１０号杂交组合，根据Ｆ２代分析结果，小粒黑豆在铁丰２４号背景下表现出有两对抗病基因，在开育１０号的背景下由４对显性抗病基因控制对３号小种的抗性，磨石黑豆在铁丰２４号背景下有两对隐性抗病基因，铁丰１８号×连毛会黑豆组合Ｆ２代分离表现为三对基因的互补作用。     

大豆种质资源对大豆孢囊线虫4号生理小种的抗性鉴定研究

本研究旨在鉴定和评价大豆种质资源对大豆孢囊线虫4号生理小种的抗性.1988-1990年在砀山县病地里对黄淮地区1800份大豆种质资源进行了抗大豆孢囊线虫4号生理小种鉴定.结果鉴定出7个抗病品种,其中2个褐色种皮,5个黑色种皮.品种的抗性与花色、茸毛色关系密切,与株高、生育期和百粒重不相关.     

Cattle grazing increases microbial biomass and alters soil nematode communities in subtropical pastures

This study focused on examining the impacts of cattle grazing on belowground communities and soil processes in humid grasslands. Multiple components in the soil communities were examined in heavily grazed and ungrazed areas of unimproved and improved bahiagrass (Paspalum notatum Flugge) pastures in south-central Florida. By using small (1-m×1-m) sampling plots, we were able to detect critical differences in nematode communities, microbial biomass, and mineralized C and N, resulting from the patchy grazing pattern of cattle. Soil samples were collected on three occasions between June 2002 and June 2003. Microbial C and N were greater (P?0.01) in grazed than in ungrazed plots on all sampling dates. Effects of grazing varied among nematode genera. Most genera of colonizer bacterivores were decreased (P?0.10) by grazing, but more persistent bacterivores such as Euteratocephalus and Prismatolaimus were increased, as were omnivores and predators. Higher numbers of persisters indicated that grazing resulted in a more structured nematode community. Some herbivores, particularly Criconematidae, were decreased by grazing. Abundance of omnivores, predators, and especially fungivores were strongly associated with C mineralization potential. Strong correlation of microbial C and N with nematode canonical variables composed of five trophic groups illustrates important links between nematode community structure and soil microbial resources. Including the analysis of nematode trophic groups with soil microbial responses reveals detection of grazing impact deeper into the hierarchy of the decomposition process in soil, and illustrates the complexity of responses to grazing in the soil foodweb. Although highly sensitive to grazing impacts, small-scale sampling could not be used to generalize the overall impact of cattle grazing in large-scale pastures, which might be determined by the intensity and grazing patterns of various stocking densities at the whole pasture level.     

Nematode succession and microfauna-microorganism interactions during root residue decomposition

The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.     

Collembolan trophic preferences determined using fatty acid distributions and compound-specific stable carbon isotope values

The trophic preferences of soil invertebrates such as Collembola are often determined by the analysis of gut contents, or through visual observations of the location of individuals. As an alternative approach, two species of Collembola, Folsomia candida and Proisotoma minuta, were offered a choice of the soil fungus Cladosporium cladosporioides or the bacterial feeding nematode Panagrellus redivivus; each exhibited distinct fatty acid profiles and stable carbon isotopic compositions. Over 21 days, the fatty acids i15:0, i17:0, 18:1(n-7) and 18:2(n-6) all increased in abundance in both collembolan species consistent with direct routing from the nematode dietary choice which contained a high concentration of these components. Collembolan fatty acid δ¹³C values increased by between 5.7 and 21.6‰ over 21 days reflecting those of the nematode diet. Therefore, both fatty acid profiles and δ¹³C values were consistent with a strong feeding preference of F. candida and P. minuta for the nematodes over the offered fungi. In fact, neither collembolan species consumed any detectable amount of C. cladosporioides. Comparison of the δ¹³C values of the 16:0 and 18:0 fatty acids (which are biosynthesised by the Collembola as well as directly incorporated from the diet) and the 16:1(n-7) and 18:2(n-6) components (which are not biosynthesised by the Collembola) demonstrated that the input of distinct pools of C can lead to large shifts in δ¹³C values between diet and consumer. The fatty acids that were not biosynthesised by Collembola better reflected the δ¹³C values of the diet helping to differentiate between biosynthesised and directly incorporated compounds; an important prerequisite in the interpretation of compound-specific δ¹³C values in trophic behaviour tests. The combination of fatty acid distributions and δ¹³C values is a significant improvement on traditional methods of examining feeding preferences, since it determines directly the assimilated dietary carbon rather than relying on indirect observations, such as the proximity of individuals to a defined food source.