Effects of Rhizosphere and Long-Term Fertilization Practices on the Activity and Community Structure of Denitrifiers Under Double-Cropping Rice Field

The soil physicochemical properties, soil denitrification rates (PDR), denitrifiers via nitrite reductases (nirK and nirS) and nitrous oxide reductase (nosZ), abundance and community composition of denitrifiers in both the rhizosphere and bulk soil from a long-term (32 year) fertilizer field experiment conducted during late rice season were investigated by using the MiSeq sequencing, quantitative PCR, terminal restriction fragment polymorphism (T-RFLP). The experiment including four treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), and organic manure and chemical fertilizer (OM). The results showed that the application of rice straw residue and organic manure increased soil organic carbon (C), total nitrogen (N), and NH₄⁺-N contents. The nirK, nirS, and nosZ copy numbers with OM and RF treatments were significant higher than that of the MF and CK treatments in the rhizosphere and bulk soil (p < 0.05). The principal coordinate analysis (PCoA) analysis showed that the different parts of root zone are the most important factors for the variation of denitrifying bacteria community, and the different fertilization treatments is the second important factors for the variation of denitrifying bacteria community. The MiSeq sequencing result showed that nirK, nirS and nosZ-type denitrifiers communities within bulk soil had lower species diversity compared with rhizosphere soil, and were dominated by Rhizobiales, Rhodobacterales, Burkholderiales, and Pseudomonadales. As a result, the application of fertilization practices had significant effects on soil N and PDR levels, and affected the abundance and community composition of N-functional microbes.     

Identifying response groups of soil nitrifiers and denitrifiers to grazing and associated soil environmental drivers in Tibetan alpine meadows

Defining response groups within N-related microbial communities is needed to predict land management effect on soil N dynamics, but information on such response groups and associated environmental drivers is scarce. We investigated the abundance and major populations of ammonia-oxidizing archaea (AOA) and bacteria (AOB), and nirS- and nirK-harboring denitrifiers under different grazing managements in Tibetan alpine meadow soils. Grazing increased AOB and AOA abundances up to 42 fold and 3.7 fold, respectively, and increased the percentage of AOB within total ammonia oxidizers from 3.1% to 10.8%. The abundance of nirK-like denitrifiers increased with grazing intensity, while the abundance of nirS-like denitrifiers tended to decrease. However, sub-groups within each of these broad groups of (de)nitrifiers responded differently to grazing. Soil nitrate was the main driver of the abundance of denitrifier sub-groups (nirK or nirS) positively responding to grazing, while soil moisture and carbon concentration were the main drivers of the abundance of denitrifier sub-groups negatively responding to grazing. AOB and nirK-harboring denitrifiers thus generally responded more positively to grazing than AOA and nirS-harboring denitrifiers, but significant functional diversity existed within each group. Our approach demonstrates the usefulness of the concept of response groups to better characterize and understand (de)nitrifier response to grazing.     

生物质炭对土壤N2O消耗的影响及其微生物影响机理

生物质炭在温室气体减排方面具有很大的发展前景,它不仅能实现固碳,对于在大气中停留时间长且增温潜势大的N₂O也能发挥积极作用。本研究采用室内厌氧培养试验,按照生物质炭与土壤质量比（0、1%和5%）加入一定量生物质炭,土壤重量含水率控制在20%。利用Robotized Incubation平台实时检测N₂O和N₂浓度变化,通过测定土壤中反硝化功能基因丰度（nirK、nirS、nosZ）分析生物质炭对N₂O消耗的影响及其微生物方面的影响机理。结果表明：经过20 h厌氧培养后,0生物质炭处理的反硝化功能基因丰度（基因拷贝数·g^-1）分别为6.80×10⁷（nirK）、5.59×10⁸（nirS）和1.22×10⁸（nosZ）。与0生物质炭处理相比,1%生物质炭处理的nirS基因丰度由最初的2.65×10⁸基因拷贝数·g^-1升至7.43×10⁸基因拷贝数·g^-1,nosZ基因丰度则提高了一个数量级,由4.82×10⁷基因拷贝数·g^-1升至1.50×10⁸基因拷贝数·g^-1,然而nirK基因丰度并无明显变化;5%生物质炭处理的反硝化功能基因丰度并未发生显著变化。试验结束时,添加生物质炭处理的N₂/（N₂O+N₂）比值也明显高于0生物质炭处理。相关性分析结果表明,nirS基因丰度和nosZ基因丰度均与N₂O浓度在0.01水平上显著相关。试验末期nirS基因丰度和nosZ基因丰度均随着N₂O浓度的降低而升高。因此在本试验中,添加1%生物质炭可显著提高nirS和nosZ基因型反硝化细菌的丰度,增大N₂/（N₂O+N₂）比值,促进N₂O彻底还原成N₂。生物质炭对于N₂O主要影响机理是增大了可以还原氧化亚氮的细菌活性,促进完全反硝化。     

Does ivermectin attract earthworms?

Purpose  

Changes in the behavior of earthworms (for example avoidance of a particular substrate) can influence the soil ecosystem. Our aim was to determine whether the earthworms Eisenia fetida and Lumbricus terrestris are able to avoid ivermectin (a veterinary endectocide belonging to the avermectins). A standard avoidance test with earthworms was conducted using standardized Lufa 2.3 soil (Speyer, Germany) and sandy soil provided by Cinkarna Celje (Slovenia).     

Epigeic earthworms increase soil arthropod populations during first steps of decomposition of organic matter

Earthworms and soil arthropods are major groups involved in soil decomposition processes. Although the interaction between these organisms can influence decomposition rates, little is known about their population dynamics during the decomposition of organic matter. In this study, we used the pig manure decomposition process to evaluate the effects of the presence of the epigeic earthworm Eisenia fetida on seven groups of soil arthropods: springtails, astigmatid, prostigmatid, mesostigmatid and oribatid mites, psocids and spiders. We carried out an experiment in which low and high doses (1.5 and 3 kg, respectively) of pig manure were applied in consecutive layers to small-scale mesocosms with and without earthworms. The presence of E. fetida increased the overall number of soil arthropods regardless of the dose of manure applied. This result was mainly due to the presence of large populations of springtails and mesostigmatid mites. Springtails were more abundant in the new layers of the mesocosms, which indicated a preference for substrates with fresh organic matter and higher microbial biomass. The other arthropod groups were consistently favored by the presence of earthworms, but remained at low densities throughout the decomposition process. Only the psocids were negatively affected by the presence of E. fetida. These results suggest that the development of large populations of soil arthropods, mainly springtails, in the mesocosms with earthworms is a characteristic feature of the initial stages of the earthworm-driven decomposition process.     

Microbial community indigenous to the earthworm Eisenia foetida

 Microbial populations of the earthworm Eisenia foetida, their casts and farmyard manure (FYM) in which E. foetida had lived were enumerated with the dilution plate method using several media. The microbial community of earthworms appeared to be similar to that of the FYM in which they had lived, while that of earthworms starved in distilled water for 24 h greatly differed from that of the FYM. The community of the starved earthworms consisted exclusively (more than 90%) of fast growers, which were defined as those that formed their colonies within 2 days, unlike that of the FYM (10–30%). About 30 isolates were randomly chosen and some physiological properties were examined. The community of starved earthworms consisted exclusively of Gram-negative, oxidase-positive, fermentative bacteria, whereas bacteria from the FYM were much more diverse and there were no fermentative bacteria in the FYM. The predominant bacteria species of the starved earthworms were identified as Aeromonas hydrophila and considered to be indigenous to the earthworm E. foetida. Received: 18 June 1999     

蚯蚓在工业固体废物和杂草vermiprocessing过程中的营养循环研究

Vermicomposting is a biotechnological process that enables the recycling of organic waste materials into manure through the combined action of earthworms and mesophilic microorganisms.In this study,a 13-week experiment was carried to vermiprocess food industry sludge mixed with diferent bedding materials including two weeds,water hyacinth and parthenium,as well as cow dung,in diferent combinations employing earthworms of the species Eisenia fetida.Eight vermibins containing one kilogram of the waste mixtures (dry weight basis) were established for vermicomposting.Vermiprocessing significantly increased nitrogen,phosphorous,and potassium contents of the mixtures.However,a decrease in pH,organic carbon,and C:N ratio was observed after vermiprocessing.The heavy metal contents in the vermicomposts were higher than the initial values but within permissible limits.These results indicated that the studied wastes can be converted into good quality manure by vermiprocessing,which indicated their agricultural values as a soil conditioner if mixed with weeds in appropriate ratios.     

Population dynamics of the earthworm Amynthas alexandri (Annelida: Megascolecidae) in a Kumaun Himalayan pasture soil

Ecological studies on earthworms were conducted in a Kumaun Himalayan pasture soil. The C:N ratio in the soil declined with increasing depth. A combination of hand-sorting and formalin application was used to sample the earthworms. Three species, Amynthas alexandri, A. diffringens (Megascolecidae), and Eisenia fetida (Lumbricidae) were found. Of the 13310 individuals collected, 99.9% were A. alexandri. The maximum density (138.8 m^-2) and biomass (25.2 g m^-2) were recorded in the wet season. More than 60% of the total earthworm numbers and biomass were recorded at 0–10 cm in depth. The mean yearly ratio of clitellate to aclitellate worms was 1:7.3.     

Chronic effects of different fertilization regimes on nirS-type denitrifier communities across the black soil region of Northeast China

Denitrification is one of the major processes causing nitrogen loss from arable soils.This study aimed to investigate the responses of nir S-type denitrifier communities to different chronic fertilization regimes across the black soil region of Northeast China.Soil samples were collected from sites located in the north(NB),middle(MB),and south(SB)of the black soil region of Northeast China,each with four chronic fertilization regimes:no fertilizer(No F),chemical fertilizer(CF),manure(M),and chemical fertilizer plus manure(CFM).Methods of quantitative polymerase chain reaction(q PCR)and Illumina Mi Seq sequencing were applied to assess the abundance and composition of denitrifier communities by targeting the nir S gene.The results showed that the M and CFM regimes significantly increased the abundances of nir S-type denitrifiers compared with No F at the three locations.The majority of nir S sequences were grouped as unclassified denitrifiers,and the different fertilizers induced little variation in the relative abundance of known nir S-type denitrifier taxa.Over 90%of the sequences were shared among the four fertilization regimes at each location,but none of the abundant operational taxonomic units(OTUs)were shared among the three locations.Principal coordinate analysis(PCo A)revealed that the communities of nir S-type denitrifier were separated into three groups that corresponded with their locations.Although similar fertilization regimes did not induce consistent changes in the nir S-type denitrifier communities,soil p H and NO-3-N content simultaneously and significantly influenced the structure of nir S-type denitrifier communities at the three locations.Our results highlight that geographical separation rather than chronic fertilization was the dominant factor determining the nir S-type denitrifier community structures,and similar chronic fertilization regimes did not induce consistent shifts of nir S-type denitrifier communities in the black soils.     

Chemical changes during vermicomposting (Eisenia fetida) of sheep manure mixed with cotton industrial wastes

Summary Castings of Eisenia fetida from sheep manure alone and mixed with cotton wastes analysed for their properties and chemical composition every 2 weeks for 3 months and compared with the same manures in the absence of earthworms. The results showed that earthworms accelerated the mineralization rate and converted the manures into castings with a higher nutritional value and degrees of humification. The castings obtained from manure mixed with cotton wastes exhibited good agronomic quality, suggesting that this kind of industrial residue may be used in vermicomposting.Work supported by Obra Social Caixa de Barcelona     

Control of cotton <Emphasis Type="Italic">Verticillium</Emphasis> wilt and fungal diversity of rhizosphere soils by bio-organic fertilizer

Cotton Verticillium wilt is a destructive soil-borne disease affecting cotton production. In this study, application of bio-organic fertilizer (BIO) at the beginning of nursery growth and/or at the beginning of transplanting was evaluated for its ability to control Verticillium dahliae Kleb. The most efficient control of cotton Verticillium wilt was achieved when the nursery application of BIO was combined with a second application in transplanted soil, resulting in a wilt disease incidence of only 4.4%, compared with 90.0% in the control. Denaturing gradient gel electrophoresis patterns showed that the consecutive applications of BIO at nursery and transplanting stage resulted in the presence of a unique group of fungi not found in any other treatments. Humicola sp., Metarhizium anisopliae, and Chaetomium sp., which were considered to be beneficial fungi, were found in the BIO treatment, whereas some harmful fungi, such as Alternaria alternate, Coniochaeta velutina, and Chaetothyriales sp. were detected in the control. After the consecutive applications of BIO at nursery and transplanting stage, the V. dahliae population in the rhizosphere soil in the budding period, flowering and boll-forming stage, boll-opening stage, and at harvest time were 8.5 × 10², 3.1 × 10², 4.6 × 10², and 1.7 × 10² colony-forming units per gram of soil (cfu g⁻¹), respectively, which were significantly lower than in the control (6.1 × 10³, 3.4 × 10³, 5.2 × 10³, and 7.0 × 10³ cfu g⁻¹, respectively). These results indicate that the suggested application mode of BIO could effectively control cotton Verticillium wilt by significantly changing the fungal community structure and reducing the V. dahliae population in the rhizosphere soil.     

Removal of polycyclic aromatic hydrocarbons from soil amended with biosolid or vermicompost in the presence of earthworms (Eisenia fetida)

Earthworms burrow through the soil thereby accumulating many lipophilic organic pollutants from the surrounding environment, so they could be used to remove polycyclic aromatic hydrocarbons (PAHs) from soil. Sterilized and unsterilized soil was contaminated with phenanthrene (Phen), anthracene (Anth) and benzo[a]pyrene (BaP), with or without added Eisenia fetida and biosolid or vermicompost. Concentrations of PAHs were monitored in soil and earthworms for 70 days. Removal of PAHs increased in soil with earthworms added as 91% of Anth, 16% BaP and 99% Phen was dissipated compared to 42%, 3% and 95% in unamended soil. The microorganisms in the gut of the earthworm contributed to PAHs removal and 100% of Phen, 63% of Anth and 58% of BaP was removed from sterilized soil with E. fetida added. Biosolid and to lesser extent vermicompost accelerated removal of PAHs from soil. Applying earthworms to a contaminated site might be an environmentally friendly way to remove hydrocarbons from soil. However, a limitation might be the cost of the large amounts of earthworms required to remove PAHs from soil and the necessity to supply them with sufficient substrate while maintaining the water content of the soil high enough for their normal functioning.     

Toxicological effects of microcystin-LR on earthworm (<Emphasis Type="Italic">Eisenia fetida</Emphasis>) in soil

Microcystin-LR (MC-LR) is a cyclic heptapeptide toxin produced by cyanobacteria in eutrophic water. It can be transferred into soil–crop systems via irrigation and cyanobacterial paste fertilization. No studies have examined the potential toxicity of MC-LR to soil animals. Therefore, in the present study, the toxicological effects of MC-LR on earthworm (Eisenia fetida), including survival, growth, reproduction, oxidative stress, and cell viability, were investigated. The LC₅₀ of MC-LR was 0.149 μg cm^?2 at 72 h based on a filter paper test and 0.460 mg kg^?1 at 14 days based on an acute soil test. MC-LR seriously affected the reproduction of earthworms. Based on hatchability, the EC₅₀ of MC-LR was 0.268 mg kg^?1, similar to environmentally relevant concentrations of microcystins. The changes in activities of superoxide dismutase, guaiacol peroxidase, catalase, and glutathione peroxidase, together with the levels of glutathione and malondialdehyde, indicated that oxidative damage and lipid peroxidation played significant roles in MC-LR toxicity. In addition, the toxicity of MC-LR in earthworms increased despite degradation of MC-LR in soil over time, possibly due to the formation of toxic metabolites of MC-LR or the bioaccumulation of MC-LR in earthworms. A reduction in the neutral red retention time along with an increase in coelomocyte apoptosis with increasing MC-LR concentrations indicated a severe damage to viability. These results suggest that environmentally relevant MC-LR concentrations in agricultural soil may cause reproductive, biochemical, and cellular toxicity to Eisenia fetida. This information can be used in ecological risk assessments on MC-LR in soil.     

Toxicological effects of TiO2 and ZnO nanoparticles in soil on earthworm Eisenia fetida

Nanoparticles (NPs) of TiO₂ and ZnO are receiving increasing attention due to their widespread applications. To evaluate their toxicities to the earthworm Eisenia fetida (Savigny, 1826) in soil, artificial soil systems containing distilled water, 0.1, 0.5, 1.0 or 5.0 g kg⁻¹ of NPs were prepared and earthworms were exposed for 7 days. Contents of Zn and Ti in earthworm, activities of antioxidant enzymes, DNA damage to earthworm, activity of cellulase and damage to mitochondria of gut cells were investigated after acute toxicity test. The results from response of the antioxidant system combined with DNA damage endpoint (comet assay) indicated that TiO₂ and ZnO NPs could induce significant damage to earthworms when doses were greater than 1.0 g kg⁻¹. We found that Ti and Zn, especially Zn, were bioaccumulated, and that mitochondria were damaged at the highest dose in soil (5.0 g kg⁻¹). The activity of cellulase was significantly inhibited when organisms were exposed to 5.0 g kg⁻¹ of ZnO NPs. Our study demonstrates that both TiO₂ and ZnO NPs exert harmful effects to E. fetida when their levels are higher than 1.0 g kg⁻¹ in soil and that toxicity of ZnO NPs was higher than TiO₂.     

Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil II. Effect of organic manures varying in N content and C:N ratio

 Nitrogen and carbon mineralization of cattle manure (N=6 g kg^–1; C:N=35), pressmud (N=17.4 g kg^–1; C:N=22), green manure (N=26.8 g kg^–1; C:N=14) and poultry manure (N=19.5 g kg^–1; C:N=12) and their influence on gaseous N losses via denitrification (using the acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) were investigated in a growth chamber simulating upland, nearly saturated, and flooded conditions. Mineralization of N started quickly in all manures, except pressmud where immobilization of soil mineral N was observed for an initial 4 days. Accumulation of mineral N in upland soil plus denitrified N revealed that mineralization of cattle manure-, pressmud-, poultry manure- and green manure-N over 16 days was 12, 20, 29 and 44%, respectively, and was inversely related to C:N ratio (R ²=0.703, P=0.05) and directly to N content of organic manure (R ²=0.964, P=0.01). Manure-C mineralized over 16 days ranged from 6% to 50% in different manures added to soil under different moisture regimes and was, in general, inversely related to initial C:N ratio of manure (R ²=0.690, P=0.05). Cumulative denitrification losses over 16 days in control soils (without manure) under upland, nearly saturated, and flooded conditions were 5, 23, and 24 mg N kg^–1, respectively. Incorporation of manures enhanced denitrification losses by 60-82% in upland, 52–163% in nearly saturated, and 26–107% in flooded soil conditions over a 16-day period, demonstrating that mineralized N and C from added manures could result in 2- to 3-fold higher rate of denitrification. Cumulative denitrification losses were maximal with green manure, followed by poultry manure, pressmud and cattle manure showing an increase in denitrification with increasing N content and decreasing C:N ratio of manure. Manure-amended nearly saturated soils supported 14–35% greater denitrification than flooded soils due to greater mineralization and supply of C.     

Ecological pre-release risk assessment of two genetically engineered, bioluminescent Rhizobium meliloti strains in soil column model systems

In order to identify potential ecological risks associated with the environmental release of two Rhizobium meliloti strains, genetically engineered with the firefly-derived luciferase gene (luc), a pre-release greenhouse investigation was conducted. The upper 4 cm of soil columns (30 cm diameter; 65 cm depth), which were filled according to the horizons of an agricultural field (loamy sand), were inoculated with seeds of Medicago sativa (alfalfa) and R. meliloti cells at approximately 5×10⁶ cells·g^–1 soil. Four treatments were tested: inoculation with a non-engineered wild type strain (2011), strain L33 (luc ⁺), strain L1(luc ⁺, recA^–) and non-inoculated controls. The fate of the engineered strains was followed by two methods: (1) selective cultivation and subsequent detection of bioluminescent colonies and (2) PCR detection of the luc gene in DNA, directly extracted from soil. Strain R. meliloti L33 declined to 9.0×10⁴ cfu·g^–1 soil within 24 weeks and to 2.8×10³ cfu·g^–1 soil within 85 weeks in the upper 25 cm of the soil columns. Decline rates for R. meliloti L1 were not significantly different. Vertical distribution analysis of the recombinant cells after 37 weeks revealed that in three of four columns tested, the majority of cells (>98%) remained above 10 cm soil depth and no recombinant cells occurred below 20 cm depth. However, in one column all horizons below 20 cm were colonized with 2.2×10⁴ to 6.8×10⁴ cfu g^–1 soil. Ecological monitoring parameters included organic substance, total nitrogen, ammonium and nitrate, microbial biomass, culturable bacteria on four different growth media and the immediate utilization of 95 carbon sources (BiologGN) by soil-extracted microbial consortia. None of the parameters was specifically affected by the genetically engineered cells. Received: 6 December 1996     

Temporal shifts in diversity and quantity of nirS and nirK in a rice paddy field soil

Denitrification is an important part of the nitrogen cycle in the environment, and diverse bacteria, archaea, and fungi are known to have denitrifying ability. Rice paddy field soils have been known to have strong denitrifying activity, but the microbes responsible for denitrification in rice paddy field soils are not well known. Present study analyzed the diversity and quantity of the nitrite reductase genes (nirS and nirK) in a rice paddy field soil, sampled four times in one rice-growing season. Clone library analyses suggested that the denitrifier community composition varied over sampling time. Although many clones were distantly related to the known NirS or NirK, some clones were related to the NirS from Burkholderiales and Rhodocyclales bacteria, and some were related to the NirK from Rhizobiales bacteria. These denitrifiers may play an important role in denitrification in the rice paddy field soil. The quantitative PCR results showed that nirK was more abundant than nirS in all soil samples, but the nirK/nirS ratio decreased after water logging. These results suggest that both diversity and quantity changed over time in the rice paddy field soil, in response to the soil condition.     

Quantification of nitrogen excretion rates for three lumbricid earthworms using 15N

 Nitrogen excretion rates of ¹⁵N-labeled earthworms and contributions of ¹⁵N excretion products to organic (dissolved organic N) and inorganic (NH₄-N, NO₃-N) soil N pools were determined at 10  °C and 18  °C under laboratory conditions. Juvenile and adult Lumbricus terrestris L., pre-clitellate and adult Aporrectodea tuberculata (Eisen), and adult Lumbricus rubellus (Hoffmeister) were labeled with ¹⁵N by providing earthworms with ¹⁵N-labeled organic substrates for 5–6 weeks. The quantity of ¹⁵N excreted in unlabeled soil was measured after 48 h, and daily N excretion rates were calculated. N excretion rates ranged from 274.4 to 744 μg N g^–1 earthworm fresh weight day^–1, with a daily turnover of 0.3–0.9% of earthworm tissue N. The N excretion rates of juvenile L. terrestris were significantly lower than adult L. terrestris, and there was no difference in the N excretion rates of pre-clitellate and adult A. tuberculata. Extractable N pools, particularly NH₄-N, were greater in soils incubated with earthworms for 48 h than soils incubated without earthworms. Between 13 and 40% of excreted ¹⁵N was found in the ¹⁵N-mineral N (NH₄-N+NO₃-N) pool, and 13–23% was in the ¹⁵N-DON pool. Other fates of excreted ¹⁵N may have been incorporation in microbial biomass, chemical or physical protection in non-extractable N forms, or gaseous N losses. Earthworm excretion rates were combined with earthworm biomass measurements to estimate N flux from earthworm populations through excretion. Annual earthworm excretion was estimated at 41.5 kg N ha^–1 in an inorganically-fertilized corn agroecosystem, and was equivalent to 22% of crop N uptake. Our results suggest that the earthworms could contribute significantly to N cycling in corn agroecosystems through excretion processes. Received: 12 April 1999     

Release, movement and recovery of 3,4-dimethylpyrazole phosphate (DMPP), ammonium, and nitrate from stabilized nitrogen fertilizer granules in a silty clay soil under laboratory conditions

 The composition of soil microbiota in four heated (350  °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g^–1 soil or 3.0 μg chlorophyll a g^–1 soil) with cyanobacteria (Oscillatoria PCC9014, Nostoc PCC9025, Nostoc PCC9104, Scytonema CCC9801, and a mixture of the four) was studied by cultural methods. The aims of the work were to investigate the potential value of cyanobacteria as biofertilizers for accelerating soil recolonization after fire as well as promoting microbiotic crust formation and to determine the microbial composition of such a crust. The inoculated cyanobacteria proliferated by 5 logarithmic units in the heated soils which were colonized very quickly and, after 2 months of incubation, the cyanobacterial filaments and associated fungal hyphae made up a matrix in which surface soil particles were gathered into crusts of up to 1.0 cm in thickness. These crusts were composed, on average, of 2.5×10¹⁰ cyanobacteria, 2.8×10⁶ algae, 6.1×10¹⁰ heterotrophic bacteria (of which 1.2×10⁸ were acidophilic, 1.3×10⁶ were Bacillus spp. and 1.5×10⁸ were actinomycetes) and 77.8 m fungal mycelium (1.4×10⁶ were fungal propagules) g^–1 crust. Counts of most microbial groups were positively correlated to cyanobacterial numbers. The efficacy of treatment depended on both the class of inoculum and the type of soil. The best inoculum was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone; however, the latter was comparatively the most favoured by the amendment. In the medium term there were no significant differences between the two inocula rates used. Biofertilization increased counts of cyanobacteria by 8 logarithmic units while heterotrophic bacteria, actinomycetes, algae and fungal propagules rose by >4 logarithmic units, acidophilic bacteria and Bacillus spp. by around 3 logarithmic units and fungal mycelia showed an 80-fold increase. The results showed that inoculation of burned soils with particle-binding diazotrophic cyanobacteria may be a means of both improving crust formation and restoring microbial populations. Received: 8 March 2000