Evaluation of suppression of rhizomania disease by earthworm (Lumbricus terrestris L.) and its effects on soil microbial activity in different sugar beet cultivars

The ability of earthworm Lumbricus terrestris L. to suppress the multiplication of Beet necrotic yellow vein virus (BNYVV) transmitted by Polymyxa betae and its effects on soil microbial activity were investigated under controlled conditions. BNYVV-infested and a combination of earthworm with BNYVV-infested soil were compared to non-infested soils for their effects on plant and root weights and virus content of two different sugar beet cultivars by using partially resistant (cv. Leila) and susceptible (cv. Arosa) cultivars to the rhizomania disease. Soil testing with sugar beet baiting plants followed by enzyme-linked immunosorbent assay (ELISA) was used to diagnose virus. The results of the statistical analyses showed that total fresh plant and root weights were negatively correlated with BNYVV infection. Addition of L. terrestris significantly enhanced plant and root weights. The earthworm-added soils had higher microbial activity such as basal soil respiration and dehydrogenase activity. The presence of earthworms in the soil did not statistically suppress BNYVV infection (p < 0.05). Sugar beet production may be enhanced by using resistant cultivars with adding L. terrestris into soil where rhizomania is present.     

Fate and dispersal of recombinant bacteria in a soil microcosm containing the earthworm Lumbricus terrestris

Summary A model ecosystem was designed containing Lumbricus terrestris in soil. The microcosm is suitable for assessing the dispersal and survival of genetically engineered microorganisms. After the inoculation of genetically engineered microorganisms their number in the worm excretions decreased continuously to reach the level of the detection limit within 50 days.     

Effect of earthworm casts on protein synthesis inAgaricus bisporus

Summary When earthworm casts were used as a casing, an early fructification, a greater stimulation in fruitbody formation, an increase in the carpophore protein content and in L-¹⁴C-leucine incorporation were observed inAgaricus bisporus. The protein-synthesizing capacity of the carpophore and its protein content were tested on samples collected 28 and 35 days after the casing. An increased L-¹⁴C-leucine incorporation of about 34% and an increased protein content of about 25% were recorded.     

Microbial activity and nutrient dynamics in earthworm casts (Lumbricidae)

Summary Microbial respiration, microbial biomass and nutrient requirements of the microflora (C, N, P) were studied in the food substrate (soil taken from the upper 3 cm of the mineral soil of a beech wood on limestone), the burrow walls and the casts of the earthworm Aporrectodea caliginosa (Savigny). The passage of the soil through the gut caused an increase in soil microbial respiration of about 90% over a 4-week period. Microbial biomass was increased only in freshly deposited casts and decreased in aging faeces to a level about 10% lower than in soil. Microbial respiration of the burrow walls was only increased over a shorter period (about 2 weeks). The microflora of the soil and the burrow walls was limited by P, whereas in earthworm casts, microbial growth was limited by the amount of available C. In aging faeces the P requirement of the microflora increased and approached that of the soil. Immobilization of phosphate in earthworm casts is probably caused by mainly abiotic processes. C mineralization by soil microflora fertilized with glucose and P was limited by N, except in freshly deposited casts. Ammonium, not nitrate, was responsible for this process. N dynamics in earthworm casts are discussed.     

The role of the earthworm Lumbricus terrestris in the transport of bacterial inocula through soil

Two laboratory experiments were used to investigate the effect of the earthworm Lumbricus terrestris on transport of genetically marked Pseudomonas fluorescens inocula through soil microcosms. The microcosms comprised cylindrical cores of repacked soil with or without earthworms. Late log-phase cells of P. fluorescens, chromosomally marked with lux genes encoding bioluminescence, were applied to the surface of soil cores as inoculated filter paper discs. In one experiment, 5 and 10 days after inoculation, cores were destructively harvested to determine concentrations of marked pseudomonads with depth relative to the initial inoculum applied. Transport of the bacteria occurred only in the presence of earthworms. In a second experiment cores were subjected to simulated rainfall events 18 h after inoculation with lux-marked bacteria at 3-day intervals over a 24-day period. Resulting leachates were analysed for the appearance of the marked bacteria, and after 28 days cores were destructively harvested. Although some marked cells (less than 0.1% of the inoculum applied) were leached through soil in percolating water, particularly in the presence of earthworms, the most important effect of earthworms on cell transport was through burial of inoculated litter rather than an increase in bypass flow due to earthworm channels.     

Microbial populations,enzyme activities and nitrogen-phosphorus-potassium enrichment in earthworm casts and in the surrounding soil of a pineapple plantation

Summary Total populations of bacteria and fungi, dehydrogenase activity (as a measure of total potential microbial activity), and urease and phosphatase activities were determined in earthworm casts and surrounding laterite soils planted to pineapple. The casts contained higher microbial populations and enzyme activities than the soil. Except for fungal populations, statistically significant (P = 0.05) increases were found in all other parameters. Microbial populations and enzyme activities showed similar temporal trends with higher values in spring and summer and lower values in winter. The earthworm casts contained higher amounts of N, P, K and organic C than the soil (P = 0.05). Selective feeding by earthworms on organically rich substrates, which break down during passage through the gut, is likely to be responsible for the higher microbial populations and greater enzyme activity in the casts.     

Effect of earthworm casts on protein synthesis in radish (Raphanus sativum) and lettuce (Lactuga sativa) seedlings

Summary The protein-synthesizing capacity of 3-day-old seedlings of radish and lettuce grown in the presence of earthworm casts was investigated using L-¹⁴-C-leucine incorporation. The results showed that earthworm casts increased protein synthesis by 24% for lettuce and 32% for radish, althought no significant differences in protein content were evident.     

Role of the anecic earthworm Lumbricus terrestris L. in the distribution of plant residue nitrogen in a corn (Zea mays)–soil system

While the benefits of earthworms to crop production are widely acknowledged, the mechanisms involved are poorly understood. We examined the effects of an anecic earthworm (Lumbricus terrestris) on the distribution of plant residue N in a corn (Zea mays)/soil system. Soil (mixed Ap and B horizons) mesocosms (10 cm diameter, 39 cm deep) were amended with ¹⁵N-labeled corn litter, inoculated with one earthworm per mesocosm (WORM) or none (CTRL), and pre-incubated for 1, 2 or 3 weeks. Earthworms and remaining plant residues were removed and sweet corn grown in the mesocosms in a greenhouse for 3 weeks. Litter, earthworms, shoots, roots and bulk and burrow soil were analyzed for total N and ¹⁵N. Plant and earthworm biomass were also determined. Earthworms had no significant effect on the N content of shoots, roots or bulk soil. Recovery of ¹⁵N ranged from 92.6 to 101.9% in CTRL and 60.2 to 83.2% in the WORM treatment. The ¹⁵N content of bulk soil in the WORM treatment was significantly higher than in CTRL and increased with pre-incubation time. Excess at.% ¹⁵N of burrow soil was 10–100 times higher than in bulk soil. Incorporation of ¹⁵N by shoots and roots was significantly higher in the WORM treatment and increased significantly with pre-incubation time only in the WORM treatment. In WORM mesocosms pre-incubated for 3 weeks, the distribution of added ¹⁵N was 9.8% in litter, 6.5% in plant, 31.5% in soil, 12.0% in earthworms and 39.8% presumably lost as gas; in CTRL mesocosms, the values were 75.7% in litter, 3.2% in plant, 13.7% in soil and 7.4% in presumed gas losses. The activities of L. terrestris altered the distribution of plant residue N significantly, increasing the transfer of N to plants and soil and enhancing losses of N in the gas phase as pre-incubation time increased.     

Inability of Near Infrared Reflectance Spectroscopy (NIRS) to identify belowground earthworm casts in no-tillage soil

Several studies have emphasised the ability of Near Infrared Reflectance Spectroscopy (NIRS) to identify surface earthworm casts in the field. However, less is known about casts deposited within the soil, which usually represent the majority found in the field. This study tested the ability of NIRS to identify belowground casts in agricultural systems. Casts and surrounding soils were sampled at depths of 20–30 cm in a loamy soil under no tillage for 12 years. To distinguish different types of cast, sizes and orientations relative to the horizontal plane were measured. NIRS analyses and analyses of carbon and nitrogen content were also performed to compare casts to surrounding soils. Casts were classified into 4 size classes, with no preferential orientation. Cast carbon and nitrogen content were not influenced by their size and did not differ from surrounding soils. PCAs performed on the NIRS data did not allow casts to be differentiated from surrounding soils, regardless of size class. However, soil aggregates were clearly differentiated probably due to their spatial distribution in the soil. Although this study did not identify specific NIRS signatures for casts, it shows the utility of this method to investigate the origin of the soil consumed by earthworms. In our case, NIRS analyses suggest that the high bulk density of the soil (1.42 g cm⁻³) forced ingestion by endogeic earthworms, simply to move around, without preferential selection for organic matter. Consequently, their casts were deposited a few mm from where they had ingested soil with similar organic matter quality.     

生物耕作对蔬菜田土壤养分及酶活性的影响

通过在上海市崇明岛西部设置的长期定位试验,探讨生物耕作对菜田土壤养分及酶活性的影响。3年结果表明,与免耕处理相比,生物耕作有助于土壤养分含量增加,其中土壤有机质、 全氮、 全磷最高增幅分别为1822%、 1745%和1332%,速效氮、 速效磷和速效钾最高增幅分别为125.0%、 432.5%和21.3%,最高值多出现在生物耕作两年和三年时,差异显著（P0.05）。同时,随生物耕作年限的增加,05 cm土层过氧化氢酶、 脲酶、 蔗糖酶和蛋白酶活性均呈增加趋势,最高增幅分别为27.78%、 951.11%、 16.11%和420.00%,分别出现在生物耕作的第三年和第二年,且差异显著（P0.05）。此系统中过氧化氢酶活性与有机质、 全磷、 速效氮、 速效磷、 速效钾和含水量等呈显著正相关,与土壤pH值呈显著负相关（P0.05）, 有机质等是土壤酶活性主要影响因子,它们单独或是综合影响酶活性; 生物耕作时间对酶活性直接影响力大小顺序为过氧化氢酶活性蔗糖酶活性脲酶活性蛋白酶活性,直接通径系数为分别为1.353、 1.070、 0.421和0.110,其主要通过有机质和速效氮正向影响酶活性。     

Potential for higher rates of denitrification in earthworm casts than in the surrounding soil

Summary Earthworms (Lumbricus terrestris L.) were cultured in the laboratory and fed on lucerne (Medicago sativa L.). Denitrification rates in the surface casts and the surrounding soil were quantified using C₂H₂-inhibition of nitrous oxide reductase. The investigation also included determination of the N₂O-formation by nitrification as well as CO₂-formation as a measure of respiration. The denitrification rates of wet earthworm casts were found to be significantly higher than those occurring in wet samples from the soil. The low N₂O-formation observed seemed to be due to denitrification. Respiration was higher in casts, indicating higher oxygen demand which resulted in more anaerobic conditions. The energy supply was probably better in casts compared with the surrounding soil.     

Novel method for the study of the population dynamics of a genetically modified microorganism in the gut of the earthworm Lumbricus terrestris

Summary A laboratory microcosm study was used to investigate the survival and population dynamics of genetically modified microorganisms (GMM) in the gut of Lumbricus terrestris. Three methods of axenic earthworm production were investigated. An antibiotic mixture of streptomycin and cycloheximide was introduced either passively, mixed with sterile soil or cellulose, or actively, by teflon catheter. Worms treated by all methods lost weight but this was least for the catheter method which was also the only method to produce axenic earthworms. Axenic earthworms were used to determine the effect of competition with indigenous gut bacteria on ingested GMM. The GMM used was Pseudomonas fluorescens, strain 10586/FAC510, with chromosomally inserted Lux genes for bioluminescence, and chromosomal resistance to rifampicin. The bacteria were grown up to the mid-exponential phase before inoculation into earthworms. Bacteria in faecal material were enumerated by dilution plate counting using selective agar. The GMM were re-isolated from the casts of both antibiotic-treated and untreated earthworms. Lower concentrations of GMM and higher concentrations of indigenous bacteria in the casts of untreated compared to antibiotic-treated earthworms suggested that competition is a fundamental control on population dynamics of the introduced bacterial inocula ingested by earthworms.The catheter method, developed in this study, is proposed as a technique to contribute to the risk assessment of environmental release of GMM.     

Leaf-litter consumption and assimilation by juveniles of Lumbricus terrestris L. (Oligochaeta,Lumbricidae) under different environmental conditions

Summary The rate of consumption of dandelion leaves per g earthworm dry weight per week was described by non-linear functions of soil temperature, soil water potential, and food availability. The optimum temperature and soil water potential for food consumption are about 22°C and-7 kPa, respectively. Zero consumption occurred at about-40 kPa. Food consumption increased with greater food availability, but only up to 1.05 (dandelion) and 1.23 (grass) g dry weight per g earthworm dry weight per week at 15°C. A general consumption function to account for all three environmental factors is given. The assimilation rate per g earthworm dry weight per week was defined as the sum of the growth rate and the maintenance rate. Maintenance was calculated according to respiratory measurements reported previously, whereas growth was measured. High temperatures and limiting environmental conditions, such as a low food availability and a low soil water potential, led to an increase in the assimilation efficiency of Lumbricus terrestris. At-7 kPa and 15°C, L. terrestris assimilated 55 and 43% of the ingested dandelion if 0.25 and 1.0 g dry weight of food was available per g earthworm dry weight per week, respectively. it is concluded that L. terrestris has a strong, direct effect on the decomposition of highly palatable plant materials.     

Influence of cropping intensity on the production and properties of earthworm casts in a leucaena alley cropping system

The effect of cropping intensity on surface cast production by earthworms was studied more than 4 years in an alley cropping system. The plots were cultivated to maize–cassava intercrop every year (100% cropping intensity), after 2 years of fallow (33% cropping intensity) and after 3 years of fallow (25% cropping intensity). Cast production was assessed by the continuous sampling technique proposed by Hauser and Asawalam (Z Pflanzenernahr Bodenkd 161:23–30, 1998). Results showed that cropping intensity enhanced cast production in the first year, did not affect it in the second and third years and decreased cast production in the fourth year. Amount of casts deposited within the alleys was highest under the hedgerow and decreased towards the middle of the alley. The concentrations of organic matter and plant nutrients were significantly higher in worm casts than in soil, irrespective of the cropping intensity and position of sample collection within the interrow space. Continuous cropping up to 6 years significantly reduced the concentrations of organic carbon, total nitrogen, available phosphorus, and exchangeable calcium, potassium and magnesium in the top 0–5 cm of the soil, irrespective of the distance from the hedgerow. Regardless of the intensity of cropping, there is a strong linear association between the quantity of casts and the amount of organic carbon, and other nutrients in casts.     

Impacts of wetting-drying cycles on short-term carbon and nitrogen dynamics in Amynthas earthworm casts

Effects of earthworm casts on soil nutrient dynamics and their responses to changing moisture availability in subtropical ecosystems remain poorly understood. This study aimed to examine short-term carbon(C) and nitrogen(N) dynamics and their interactions with wetting-drying cycles in three different structural forms(i.e., granular, globular, and heap-like) of Amynthas earthworm casts. The rates of C and N mineralization in the earthworm casts were examined under two different wetting-drying cycles(i.e., 2-d and 4-d wetting intervals) using a rainfall simulation experiment. After three simulated rainfall events, subsamples of the earthworm casts were further incubated for 4 d for the determination of CO_2 and N_2O fluxes. The results of this study indicated that the impacts of wetting-drying cycles on the short-term C and N dynamics were highly variable among the three cast forms, but wetting-drying cycles significantly reduced the cumulative CO_2 and N_2O fluxes by 62%–83% and 57%–85%, respectively, when compared to the control without being subjected to any rainfall events. The C mineralization rates in different cast forms were affected by the amount of organic substrates and N content in casts, which were associated with the food preference and selection of earthworms. Meanwhile, the cumulative N_2O fluxes did not differ among the three cast forms. Repeated wetting and drying of casts not only enhanced aggregate stability by promoting bonds between the cast particles, but also inhibited microbial survival and growth during the prolonged drying period, which together hindered decomposition and denitrification. Our findings demonstrated that the interactions between the structural forms, aggregate dynamics, and C and N cycling in the earthworm casts were highly complex.     

Microfungal communities in soil,litter and casts of Lumbricus terrestris L. (Lumbricidae): a laboratory experiment

The anecic earthworm Lumbricus terrestris L. was kept in laboratory microcosms containing beech forest soil without litter, with beech leaf litter or with lime leaf litter. The structure of microfungal communities in soil, litter and fresh and aged (100 days) earthworm faeces was analysed using the washing and plating technique. The passage of mineral soil through the gut of L. terrestris affected the structure of the fungal community only little. In contrast, in the litter treatments the structure of the fungal community in fresh earthworm casts significantly differed from that in soil and litter. The majority of soil and litter inhabiting fungi survived passage through the gut of L. terrestris and the fungal community in casts consisted of a mixture of soil and litter inhabiting fungi. However, the frequency of Cladosporium spp., Alternaria spp., Absidia spp., and other taxa was strongly reduced in fresh casts. The degree of colonization of litter particles (number of isolates per number of plated particles) also decreased, but some fungi (mainly Trichoderma spp.) benefited from gut passage and flourished in fresh casts. During ageing of cast material the dominance structure of the fungal community changed. Both the degree of colonization of organic particles and the species diversity increased and approached that in soil. However, the structure of the fungal community in casts remained cast specific even after 100 days of incubation. It is concluded that the feeding and burrowing activity of L. terrestris accelerates the colonization of litter by the edaphic mycoflora but also extends the range of occurrence of litter-associated fungi into mineral soil layers.     

富铝性湿润富铁土中锑对小白菜的生理响应特性以及土壤酶活性的影响

High concentrations of antimony(Sb) in soils and vegetables can cause potential health risk. However, the effect of Sb on the growth and response of crops are not well known and to date, there is still no Sb limit standard for Allitic Udic Ferrisols in China. In this study, a greenhouse experiment was carried out to investigate the effect of antimony(Sb) on biomass, physiological performances,and macro- and micronutrient element concentrations of green Chinese cabbage(Brassica chinensis L.), as well as enzyme activities,in Allitic Udic Ferrisols from Hunan Province, China. Antimony was supplied at rates of 0(control), 2, 5, 10, 20, and 50 mg kg-1and thus with the background value of 1.0 mg kg-1, the Sb concentrations in the treated soil samples were 1, 3, 6, 11 21, and 51 mg kg-1, respectively. The results showed the leaf biomass and ascorbic acid content of cabbage significantly(P < 0.05) decreased by 30.6% and 48.3%, respectively, and soil urease and dehydrogenase activities also significantly(P < 0.05) decreased by 33.6%and 32.5%, respectively, when soil Sb concentration was 21 mg kg-1as compared with the control. The uptake of essential nutrient elements such as Mg, Cu, and Zn by cabbage was obviously affected, while the leaf soluble sugar content slightly changed when the soil Sb concentration exceeded 21 mg kg-1. Based on cabbage physiological responses and soil enzyme activities, the permissible concentration of 21 mg kg-1for Sb in Allitic Udic Ferrisols should be recommended.