金沙江干热峡谷中退化的土壤生态系统生物学特征初探

Distribution characteristics of soil animals,microorganisms and enzymatic activity were studied in the dry red soil and Vertisol ecosystems with different degradation degrees in the Yuanmou dry hot valley of the Jinsha River,China.Results showed that Hymenoptera,Araneae and Collembola were the dominant groups of soil animals in the polts studied.The numbers of groups and individuals and density of soil animals in the dry red soil series were higher than those in the Vertisol series,and the numbers of individuals and density of soil animals decreased with the degree of soil degradation.Bacteria dominated microbiococnosis not only in the dry red soils but also in the Vertisols.Microbial numbers of the dry red soil series were higher than those of Vertisol series,and decreased with the degree of soil degradation.The activities of catalase,invertase,urease and alkaline phosphatase declined with the degradation degree and showed a significant decline with depth in the profiles of both the dry red soils and the Vertisols,but activities of polyphenol oxidase and acid and neutral phosphatase showed the same tendencies only in the Vertisols.It was concluded that the characteristics of soil animals,microorganisms and enzymatic activity could be used as the bio-indicators to show the degradation degree of the dry red soils and Vertisols.Correlation among these soil bio-indicators was highly significant.     

东北黑土农业生态系统线虫多样性研究

The diversity and distribution patterns of soil nematode communities in phaeozem agroecosystems of Northeast China were assessed to evaluate nematode taxonomic diversity and functional diversity in relation to climatic condition and soil characteristics in human modified landscape.Along the latitudinal gradient,soil samples were collected from north (Hailun) to south (Gongzhuling) down to a depth of 100 cm with intervals of 0-20,20-40,40-60,60-80,and 80-100 cm.The nematode abundance and taxonomic diversity (generic richness) were lower at Hailun than at other sites,and higher values of evenness were observed at Hailun and Harbin than at Dehui and Gongzhuling.Nematode faunal analysis revealed that soil food web at Hailun was successionally more mature or structured,and the environment little disturbed,while at Harbin and Gongzhuling,the soil food web was degraded with stressed environment.The environmental variables relevant in explaining the patterns of nematode distribution and diversity in phaeozem agroecosystems,using canonical correspondence analysis (CCA),were the mean annual temperature,total nitrogen,electrical conductivity,mean annual precipitation,and other soil properties.Among these variables,the mean annual temperature was a relatively important factor,which could explain 29.05% of the variations in nematode composition.     

美国俄勒冈州有机与传统农业生态系统间土壤生物区的比较

Soil samples at 0--10 cm in depth were collected periodically at paired fields in Corvallis, Oregon, USA to compare differences in soil microbial and faunal populations between organic and conventional agroecosystems Results showed that the organic soil ecosystem had a significantly higher (P < 0.05) average number or biomass of soil bacteria; densities of flagellates, amoebae of protozoa; some nematodes, such as microbivorous and predaceous nematodes and plant-parasitic nematodes; as well as Collembola. Greater numbers of Rhabditida (such as Rhabditis spp.), were present in the organic soil ecosystem while Panagrolaimus spp. Were predominant in the conventional soil ecosystem. The omnivores and predators of Acarina in the Mesostigmata (such as Digamasellidae and Laelapid), and Prostigmata (such as Alicorhaiidae and Rhagidiidae), were also more abundant in the organic soil ecosystem. However, fungivorous Prostigmata (such as Terpnacaridae and Nanorchestidae) and Astigmata (such as Acarida) were significantly higher (P < 0.05) in the conventional soil ecosystem, which supported the finding that total fungal biomass was greater in the conventional soil ecosystem. Seansonal variations of the population depended mostly on soil moisture condition and food web relationship. The population declined from May to October for both agroecosystems. However, higher diversities and densities of soil biota survived occurred in the organic soil ecosystem in the dry season.     

土层深度和季节变化对保护地西瓜连作土壤中丛枝菌根真菌群落结构的影响

The characteristics of arbuscular mycorrhizal fungal (AMF) community structure in various soil depths and growing seasons of watermelon (Citrullus vulgaris) grown in commercial greenhouses in Daxing of Beijing and Weifang and Laiyang of Shandong, China were investigated using both morphological identification and denaturing gradient gel electrophoresis. The sampled soils had been used for continuous greenhouse production of watermelon for 0, 5, 10, 15, or 20 years. Glomus claroideum was the dominant species in the greenhouse soils planted for 5, 10, and 15 years in Laiyang, while Glomus mosseae and Glomus etunicatum were dominant in the nearby open farmland soil. Sorenson’s similarity index of AMF community composition ranged from 0.67 to 0.84 in the soils planted for 5 years, and from 0.29 to 0.33 for 20 years among the three locations. Spore abundance, species richness, and the Shannon index were highest near the soil surface (0-10 cm) and decreased with soil depth, and higher in June and October than in August and December. Canonical correspondence analysis showed that available P and the number of years that soil had been used for greenhouse production were the main factors contributing to the variance of AMF community composition. It was concluded that the community structure of AMF was mainly influenced by soil available P and planting time of watermelon as well as by soil depth and seasonal variation in the commercial greenhouse.     

土壤微食物网对旱改水不同稻作年限土地利用变化的响应

Land use changes affect belowground ecosystems.During the past few decades,land use in Northeast China has changed considerably,and the area of paddy fields has increased rapidly from upland.In this study,soil characteristics and soil biotic community in paddy fields with different years of rice cultivation were measured to examine the effects of land use change from upland to paddy fields on soil micro-food web.The upland maize fields were selected as control and the microbial community composition was characterized using phospholipid fatty acids (PLFAs) analysis.The microbial biomass (total PLFA),bacteria biomass,and fungi biomass were higher in the 20-40-year (late-stage) than 1-10-year (early-stage) paddy fields.The abundances of total nematodes and bacterivores were lower in the early-stage than late-stage paddy fields.The abundance of herbivores was the highest in the early-stage paddy fields but that of omnivore-predators was the highest in the late-stage paddy fields.Structural equation model indicated that soil food web was developed and structured after 20 years of paddy cultivation.Our results suggested that soil micro-food web may be a good indicator for soil development and stabilization of paddy fields following land use change.     

利用PCR-DGGE技术研究长期自然恢复、种植作物和裸地条件下黑土土壤细菌群落结构变化

Soil microbial biomass and community structures are commonly used as indicators for soil quality and fertility. A investigation was performed to study the effects of long-term natural restoration, cropping, and bare fallow managements on the soil microbial biomass and bacterial community structures in depths of 0--10, 20--30, and 40--50 cm in a black soil (Mollisol). Microbial biomass was estimated from chloroform fumigation-extraction, and bacterial community structures were determined by analysis of 16S rDNA using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Experimental results showed that microbial biomass significantly declined with soil depth in the managements of restoration and cropping, but not in the bare fallow. DGGE profiles indicated that the band number in top 0--10 cm soils was less than that in depth of 20--30 or 40--50 cm. These suggested that the microbial population was high but the bacterial community structure was simple in the topsoil. Cluster and principle component analysis based on DGGE banding patterns showed that the bacterial community structure was affected by soil depth more primarily than by managements, and the succession of bacterial community as increase of soil depth has a similar tendency in the three managements. Fourteen predominating DGGE bands were excised and sequenced, in which 6 bands were identified as the taxa of Verrucomicrobia, 2 bands as Actinobacteria, 2 bands as α-Proteobacteria, and the other 4 bands as δ-Proteobacteria, Acidobacteria, Nitrospira, and unclassified bacteria. In addition, the sequences of 11 DGGE bands were closely related to uncultured bacteria. Thus, the bacterial community structure in black soil was stable, and the predominating bacterial groups were uncultured.     

Impact of soil fumigation practices on soil nematodes and microbial biomass

This study was designed to understand the impact of methyl bromide (MB) (CHaBr) and its alternatives on both free-living and root-knot nematodes in the soil. A randomized complete block experiment with six treatments and 4 replicates (each replicate in a separate greenhouse) was established in Qingzhou, Shandong Province, China. In addition to MB and untreated control (CK) treatments there were four alternative soil fumigation practices including MB virtually impermeable films (VIF), metam sodium (MS), MS VIF and soil solarization combined with selected biological control agents (SS BCA). Two tomato (Lycopersicum esculentum Mill.) cultivars, cv. Maofen-802 from the Xian Institute of Vegetable Science, China, and cv. AF179 Brillante from the Israeli Hazera Quality Seeds, were selected as test crops. The results indicated that Rhabditidae was the most dominant population with percentage abundance as high as 85% of the total number of identified free-living nematodes, followed by that of Cephalobidae. Methyl bromide and its alternatives except for the non-chemical SS BCA treatment controlled the target pest, root-knot nematodes. Also, the impact of the three chemical alternatives on free-living nematode number and functional group abundance was similar to the impact associated with a typical methyl bromide application. Chemical fumigation practices, especially that with MB, significantly reduced the number of nematodes in the soil and simultaneously significantly reduced the number of nematode genera thereby reducing nematode diversity. All the four soil chemical fumigation activities decreased soil microbial biomass and had an obvious initial impact on microorganism biomass. Furthermore, both plant-parasitic and fungivore nematodes were positively correlated with soil microbial biomass.     

传统耕作和免耕的红壤生态系统土壤动物种群的分异

In a field experiment ,the popultions of major soil fauna groups including earthworms,enchytraeids,arthropods and nematodes were examined in conventional tillage(CT) and no-tillage(NT) red soil ecosystems to evaluate their responses to tillage disturbance.Earthworms,macro- and micro-arthropods were stimulated under NT with earthworms showing the highest population increase by four times ,while enchytraeids and nematodes favored CT system predicting certain adaptability of these animals to plow-disturbed soil envi-ronment ,On the basis of relative response index it was found that soil fauna was more sensitive to tillage than soil resource base(C and N pools) and microflora.The population structure of soil fauna was also affected by tillage treatments.Analysis on nematode trophic groups showed that bacteria-feeding and plant parasitic nematodes were more abundant in CT soil whereas the proportions of fungivores and onmivore-predators increased in NT soil.Possible reasons for the differentiaion in both size and structure of the fauna populaion were discussed and the ecological significance involved in these changes was emphasized.     

外源铬对小白菜(Brassica chinensis L.)根际土壤微生物生物量和磷脂脂肪酸的剖面分布特征的影响

The effects of root activity on microbial response to cadmium （Cd） loading in the rhizosphere are not well understood. A pot experiment in greenhouse was conducted to investigate the effects of low Cd loading and root activity on microbial biomass and community structure in the rhizosphere of pakchoi （Brassica chinensis L.） on silty clay loam and silt loamy soil. Cd was added into soil as Cd（NO3）2 to reach concentrations ranging from 0.00 to 7.00 mg kg-1. The microbial biomass carbon （MBC） and community structure were affected by Cd concentration, root activity, and soil type. Lower Cd loading rates （〈 1.00 mg kg-1） stimulated the growth of pakchoi and microorganisms, but higher Cd concentrations inhibited the growth of microorganisms. The content of phospholipid fatty acids （PLFAs） was sensitive to increased Cd levels. MBC was linearly correlated with the total PLFAs. The content of general PLFAs in the fungi was positively correlated with the available Cd in the soil, whereas those in the bacteria and actinomycetes were negatively correlated with the available Cd in the soil. These results indicated that fungi were more resistant to Cd stress than bacteria or actinomycetes, and the latter was the most sensitive to Cd stress. Microbial biomass was more abundant in the rhizosphere than in the bulk soil. Root activity enhanced the growth of microorganisms and stabilized the microbial community structure in the rhizosphere. PLFA analysis was proven to be sensitive in detecting changes in the soil microbial community in response to Cd stress and root activity.     

在温室和室外管理措施下有机和矿物肥料对土壤物理性质的长期效应研究

To evaluate the use of organic amendments as an alternative to conventional fertilization,a 10-year experiment on a loam soil was conducted under a crop rotation system in both greenhouse and outdoor plots applied with chemical fertilizers (NPK) and vegetal compost (organic fertilizer) in the Guadalquivir River Valley,Spain.The effect of these two different fertilization regimes on the soil physical properties was evaluated.Soil organic carbon (OC),soil bulk density (BD),soil water retention (WR),available water content (AWC),aggregate stability (AS),and soil physical quality (Dexter’s index,S) were determined.The use of organic fertilizer increased OC and resulted in a significant increase in AS and a decrease in BD compared to the mineral fertilizer application in both greenhouse and outdoor plots.The outdoor plots showed the lowest BD values whereas the greenhouse plots showed the highest AS values.In the last years of the 10-year experiment the S parameter was significantly higher in organic fertilizer plots,especially for greenhouse plots.At the end of the study period,there were no significant differences in WR at field capacity (FC) between treatments in both systems;the AWC was also similar in the greenhouse plots but higher in the mineral outdoor plots.In mineral fertilizer treatments,a small improvement in the physical properties was also observed due to the utilization of less aggressive tillage compared with the previous intensive cropping system.Physical soil properties were correlated with soil OC.The sustainable management techniques such as the use of organic amendments and low or no tillage improved soil physical properties,despite the differences in management that logically significantly affected the results.     

Effects of organic mulches on soil microfauna in the root zone of apple: implications for nutrient fluxes and functional diversity of the soil food web

A variety of organic materials (e.g. composts, paper recycling wastes, hay) can be used as in-row mulches in perennial horticultural cropping systems such as high density apple orchards. As organic materials with variable properties, such mulches can be expected to have variable effects on structure of the soil food web and mineralisation of N and P in the root zone. The overall objectives of this study were to: (1) assess the effects of a selection of organic mulches on the abundance of protozoa and nematode trophic groups; (2) use the model of Hunt et al. [Biol. Fertil. Soils 3 (1987) 393] to assess the implications of changes in microfaunal abundance for microbial turnover and N mineralisation; and (3) determine effects of the mulches on nematode indicators of increased microbial production/turnover and functional diversity of the soil food web. Organic mulch treatments commenced in 1994 and included shredded office paper, municipal biosolids, shredded paper applied over municipal biosolids, shredded paper applied over municipal compost, alfalfa hay, and black polyethylene fabric. The control was conventional tree-row weed management with glyphosate. Biosolids and municipal compost treatments were re-applied in 1997. Protozoan abundance was determined in 1998, 1999 and 2000. Nematode community structure was assessed in 1998, 1999, and twice in 2000. Nematode community parameters evaluated included: abundance of bacterivorous, fungivorous, omnivorous and predacious nematodes; abundance of the root-lesion nematode, Pratylenchus penetrans; absolute and relative abundances of enrichment opportunist nematodes (Rhabditidae+Diplogasteridae+Panagrolaimidae); Simpson’s diversity; evenness; and the indices of nematode community enrichment (EI) and structure (SI) described by Ferris et al. [Appl. Soil Ecol. 18 (2001) 13]. Measurements of the abundance of enrichment opportunists and the EI were evaluated as indicators of enhanced nutrient fluxes. Diversity and the SI were evaluated as indicators of changes in functional diversity of the soil food web.The abundance of protozoa and bacterivorous nematodes, and estimated fluxes of N and P through the microfauna, were greater under all combinations of biosolids or municipal compost and shredded paper than under the control and plastic mulch. The abundance of enrichment opportunist nematodes and the EI were also consistently greater under combinations of biosolids or municipal compost and shredded paper. The abundance of enrichment opportunists and EI were both also correlated with leaf P, providing additional evidence to support the use of these parameters as indicators of enhanced turnover of microbial biomass and nutrients. The SI was greatest under shredded paper and shredded paper applied over municipal compost, and least under municipal biosolids and alfalfa hay. Population densities of P. penetrans were reduced under shredded paper mulch relative to the control and biosolids alone.     

An analysis of food-web structure and function in a shortgrass prairie,a mountain meadow,and a lodgepole pine forest

Summary The structure of the below-ground detrital food web was similar in three different semiarid vegetation types: lodgepole pine (Pinus contorta subsp. latifolia), mountain meadow (Agropyron smithii), and shortgrass prairie (Bouteloua gracilis). The densities of component food-web functional groups and the response to removal of component groups, differed however. As measured by biomass, bacteria were dominant in the meadow and prairie, while fungi were dominant in the forest. Resourde-base dominance was reflected in consumer dominance, and both directly correlated with the form of inorganic N present. Bacterial-feeding nematodes were numerically dominant in the meadow and prairie, while microarthropods were dominant in the forest. Ammonium-N was the dominant form in the forest, while nitrate —nitrite-N was the more important form in both bacterial-dominated grasslands.Addition of a biocide solution containing carbofuran and dimethoate reduced the numbers of both microarthropods and nematodes. In the bacterial-dominated grasslands, these reductions resulted in no apparent effect on bacterial densities because one group of bacterial consumers (protozoa) increased following the decrease in bacteria-feeding nematodes, in increased fungal biomass, and in increased soil inorganic N. Conversely, in the forest, following the biocide-induced reduction in consumers, the total fungal biomass decreased, but inorganic-N levels increased. The meadow appeared to be the most resilient of the three ecosystems to biocide disturbance, as both nematode and arthropod numbers returned to control levels more rapidly in the meadow than in the prairie or the forest.     

Responses of grassland soil nematodes and protozoa to multi-year and single-year applications of dairy manure slurry and fertilizer

In order to improve understanding of how long-term use of manure affects nitrogen cycling processes, the effects of multiple years of manure applications on abundance of protozoa and nematode community structure were assessed. Plots of a grass sward in the Fraser Valley of British Columbia were either left untreated or were treated with dairy manure slurry or fertilizer, each at 50 or 100 kg NH₄-N ha⁻¹, two to four times per year for six consecutive years. Nematode community structure and protozoan abundance were determined at 19 sample dates during the fourth (1997), fifth (1998) and sixth (1999) years of application. Protozoa, bacterivorous nematodes and fungivorous nematodes were consistently more abundant in soil treated with manure at both rates than in fertilized and untreated soil, indicating that microbial turnover and flux of nutrients through the soil food web was enhanced in manured soil relative to fertilized or untreated soil. The Maturity Index (MI) and the MI2-5 were both reduced by fertilization and manure, relative to the control. The MI for the manure treatment was lower than for the fertilizer treatment as a result of greater relative abundance of enrichment opportunist nematodes in manure-treated soil. Accordingly, the MI2-5 did not differ between the manure and fertilizer treatments, suggesting that with the exception of enrichment opportunists fertilizer and manure have similar effects on structural complexity of the soil food web.Populations of micro-fauna were also assessed through 1998 and 1999 in subplots that had been treated with manure or fertilizer for four years and stopped receiving manure or fertilizer in 1998, and in subplots given manure in 1998 that had previously either been fertilized or left untreated. Protozoa and bacterivorous and fungivorous nematodes remained more abundant through 1998 and 1999 in previously manure-treated plots than in previously fertilized plots, indicating that the cumulative effects of manure application on enhancement of microbial production can be detected through at least two growing seasons after applications cease. Application of manure for one year to previously non-treated or fertilized soil raised the abundance of protozoa and bacterivorous and fungivorous nematodes to levels comparable to continuously manured soil.     

Structure of the microbial biomass and trophic groups of nematodes in soddy-podzolic soils of a postagrogenic succession in the southern taiga (Tver oblast)

The structure of the microbial biomass and trophic nematode groups were studied in soddy-podzolic soils under phytocenoses of a secondary succession initiated by the growth of forests on agricultural lands in the southern taiga. The microbial biomass became greater with the increasing amount of fungal mycelium, and the bacterial pool little changed in these soils. Bacteriovorous nematodes predominated (64% of the total number of nematodes) in the soils of a potato field, where the bacterial biomass was maximal; it was greater or close to the fungal biomass. In the soil under a mown meadow, where the fungal biomass was greater, the populations of fungivorous and bacteriovorous nematodes were close in number and share in the nematode complex (by 40%). In the soil under a spruce forest (climax stage), the main biomass pool was composed of fungi (97%), whose biomass is maximal, while fungivorous nematodes and nematodes with a mixed type of feeding occupy the dominant positions (69% in the nematode complex). In the course of the succession, the number of fungivorous and bacteriovorous nematodes decreased, but their ratio increased from 0.4 in the soil of the potato field to 0.8–1.0 under the meadows and mixed forest and to 2.0 in the soil under the sorrel spruce forest. These changes corresponded to the increasing microbial pool and the share of the fungal biomass in it.     

Effects of organic,low input,conventional management practices on soil nematode community under greenhouse conditions

A comparative study of organic, low input, conventional vegetable greenhouse systems was conducted to assess the effect of management practices on the soil nematode community. Bacterivores were the most dominant trophic group in all three systems with a mean proportion of over 80%, followed by omnivore-carnivores. In general, organic management practices increased the abundance of total nematodes, bacterivores, fungivores, and omnivore-carnivores in comparison with low input and conventional management practices. Though inhibitory effects of plant feeders were found in organic and low input systems, these effects were more evident in organic systems. However, small differences were observed in the composition of trophic groups and fauna analysis. All three systems displayed enriched soil conditions and structured food webs. We inferred that the bottom-up effect resulting from organic input in the soil food web may play a more important role than the disruption effects under our high input greenhouse conditions. The Shannon index (H′) and genus dominance (λ) suggested that in greenhouse conditions, excessive manure input would cause a decrease in nematode diversity but increase the dominance, particularly for enrichment opportunists. We concluded that management practices under greenhouse conditions were more influential on nematode biomass (including trophic groups) than community structure.     

Cover crops alter the soil nematode food web in banana agroecosystems

Cover crops are increasingly being used in agriculture, primarily for weed or erosion management. The addition of cover crops increases the primary productivity of the system and diversifies basal resources for higher trophic levels. How increases in the quality and quantity of basal resources affect bottom-up and top-down control remains a key question in soil food web ecology. We evaluated the response of the nematode community to the introduction of cover crops between rows of a banana plantation. We measured changes in nematode food web structure and inferred the prevalence of bottom-up and top-down effects on the abundance of phytophagous nematodes (i.e., plant-feeding and root-hair-feeding species) 1.5 years after plots with cover crops (Poaceae or Fabaceae species) or bare soil were established. The addition of a cover crop greatly affected the structure and the abundance of the soil nematode community 1.5 years after planting. The abundance of all trophic groups except for plant-feeding nematodes tended to increase with the addition of cover crops. The Shannon–Weaver diversity index and the enrichment index increased with the addition of cover crops, indicating that opportunistic, bacterivorous and fungivorous nematodes benefited from the added resources. Plant-feeding nematodes were least abundant in plots with Poaceae cover crops, while bacterivorous, omnivorous, and root-hair-feeding nematodes were more abundant with Fabaceae cover crops than with bare soil, indicating that cover crop identity or quality greatly affected soil food web structure. Bottom-up effects on all trophic groups other than plant-feeding nematodes were evident with Poaceae cover crops, suggesting an top-down control of plant-feeding nematodes by omnivorous nematodes. Conversely, plant-feeding nematodes were evidently not suppressed in Fabaceae cover crops, perhaps because bottom-up effects on omnivorous nematodes were weaker (hence, top-down control by omnivorous nematodes was weaker), and because Fabaceae cover crops probably served as good hosts for some plant-feeding nematodes.     

Integration of cover crops and vermicompost tea for soil and plant health management in a short-term vegetable cropping system

Short-term vegetable crop production often involves frequent tillage and other farm activities that results in disturbed soil food web communities. A less disturbed soil community would have a more structured soil food web which contains soil fauna higher up in the food web hierarchy, thus higher integrity in soil nutrient cycling. The objective of this study is to examine if strip-till cover cropping and drenching soil with vermicompost tea could improve soil food web structure in a short-term agroecosystem. Two field trials were conducted in Waialua, HI, USA to evaluate the effect of strip-till planting of sunn hemp (SH, Crotalaria juncea) or crimson clover (Trifolium incarnatum) cover crops in a zucchini (Cucurbita pepo) cropping system. At zucchini planting, each cover crop plot was split to receive four soil treatments: fertilizer (F, chicken pellet), compost tea (CT), fertilizer plus compost tea (F + CT), and none. Compost tea was prepared from chicken manure based vermicompost aerated overnight in water at 1:10 (v:v). Planting of SH increased bacterivorous nematodes and suppressed plant-parasitic nematodes throughout both zucchini cropping cycles, but did not enhance the numbers of omnivorous or predatory nematodes. Crimson clover did not enhance beneficial nematodes nor suppress plant-parasitic nematodes. Adding CT to F suppressed the key plant-parasitic nematodes only at the initial stage of the zucchini growth, increased percentage of predatory or omnivorous nematodes only toward the end of zucchini crops, and increased the structure index at harvest in the first trial. Zucchini yield was increased by planting of SH but not by drenching of CT. Despite the benefits of CT in improving the soil food web structure, a correlation analysis revealed that zucchini yields were correlated to the reduction in the percentage of fungivorous nematodes at planting, an increase in the percentage of bacterivorous nematodes at harvest, and to reduction in the percentage of plant-parasitic nematodes at harvest.     

“绿色南京”林业建设新增林地的土壤生物的群落结构

于2008年夏天选择三个典型样点对"绿色南京"林业建设新增林的土壤生物多样性的群落特征进行研究。结果表明:在三个样点中,共捕获地表凋落物节肢动物1305只,隶属12纲21目,其中真螨目为优势种群,占总节肢动物的70%,常见种群或稀有种群分别为11目和14目。由于机场高速杨树防护林秣陵镇西段(样点III)真螨目的高度集中,其优势度最高,而多样性指数、均匀度指数和丰富度指数均最低;土壤线虫优势种群为植食线虫和食细菌线虫,而食真菌、捕食、杂食线虫均为常见种群;土壤原生动物中,鞭毛虫为优势种群,占原生动物总个体数的70～90%,其次为变形虫,而纤毛虫比例最小,在1～5%左右;新增林地在一定程度上改变了土壤微生物的群落结构。     

Interplay of omnivory, energy channels and C availability in a microbial-based soil food web

 To study the effects of omnivory on the structure and function of soil food webs and on the control of trophic-level biomasses in soil, two food webs were established in microcosms. The first one contained fungi, bacteria, a fungivorous nematode (Aphelenchoides saprophilus) and a bacterivorous nematode (Caenorhabditis elegans), and the second one fungi, bacteria, the fungivore and an omnivorous nematode (Mesodiplogaster sp.) feeding on both bacteria and the fungivore. Half of the replicates of each food web received additional glucose. The microcosms were sampled destructively at 5, 9, 13 and 19 weeks to estimate the biomass of microbes and nematodes and the soil NH₄ ⁺-N concentration. The evolution of CO₂ was measured to assess microbial respiration. Microbial respiration was increased and soil NH₄ ⁺-N concentration decreased by the addition of glucose, whereas neither was affected by the food-web structure. Supplementary energy increased the biomass of fungi and the fungivore, but decreased the biomass of bacteria, the bacterivore and the omnivore. The omnivore achieved greater biomass than the bacterivore and reduced the bacterial biomass less than the bacterivore. The biomass of the fungivore was smaller in the presence of the omnivore than in the presence of the bacterivore at three sampling occasions. Fungal biomass was not affected by food-web structure. The results show that the effects of the omnivore were restricted to its resources, whereas more remote organisms and soil processes were not substantially influenced. The results also indicate that the presence of an omnivore does not necessarily alter the control of populations as compared with a food web containing distinct trophic levels, and that the fungal and bacterial channels may respond differently to changes in energy supply. Received: 15 December 1997