The ratio of fungal to bacterial biomass (F/B) in the mineral soil of a burned Japanese red pine forest was determined by two different methods, the substrate-induced respiration inhibition (SIRIN) method and the microscopic method. The values of the F/B ratio were 2.4 by the SIRIN method and 9.5 by the microscopic method in the mineral soil of the burned pine forest. Lower F/B ratio in the SIRIN method might be due to the insufficient stimulation of microbial respiration by glucose added to the soil and incomplete suppression of substrate-induced respiration by antibiotics. The F/B ratios determined by the two methods reflected the predominance of the fungal population in a burned pine forest soil, presumably because the fungal population was more successful in the overall competition with the bacterial population in soils with lower available carbon content such as the pine forest soils.

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The seasonal changes in the microbial biomass and the rate of CO_2 evolution were examined in situ in a volcanic soil with different land uses (arable land, orchard and forest sites) in Tokyo. The microbial biomass of the soil at a depth of 0-20 cm was almost constant at 30 g C m^<-2> for the arable land, 35 g C m^<-2> for the orchard or 110 g C m^<-2> for the forest site. The relationship between the rate of CO_2 evolution (R, g C m^<-2> day^<-1>) and the soil temperature (t, ℃) at a depth of 5 cm was as follows: R=0.442e^<0.0655t> (r=0.91) for the arable land, R=0.544e^<0.0624t> (r=0.94) for the orchard or R=0.418e^<0.0833t> (r=0.97) for the forest site. The rate of CO_2 evolution under field conditions in the arable land, the orchard or the forest site was estimated to be 1.6 g C m^<-2> day^<-1> (600 g C m^<-2> year^<-1>), 1.7 g C m^<-2> day^<-1> (610 g C m^<-2> year^<-1>) or 1.3 g C m^<-2> day^<-1> (490 g C m^<-2> year^<-1>), respectively, by using the annual mean soil temperature of 20℃, 18℃ or 14℃, respectively. The contribution of the respiration from roots and visible invertebrates to the total soil respiration was relatively small, i.e., the amount of respiration from soil microbes in the arable land, the orchard or the forest site was estimated to be 99%, 89% or 77% of the total CO_2 evolution from soil, respectively. Based upon these results, the rate of microbial respiration per unit biomass was estimated to be 54, 43 or 9 mg C g^<-1> biomass C day^<-1> for the arable land, the orchard or the forest site, respectively. Assuming that the yield coefficient of the soil microbes is 0.1 under field conditions, it was suggested that the microbial biomass could reproduce only about twice a year in the arable land and the orchard site, or 0.3 times a year in the forest site.

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The fungal or bacterial biomass in some forest or arable sites of a volcanic soil in Tokyo was measured by the direct count method employing sonication to disperse soil particles and phenolic aniline blue as a stain. Almost 100% of the biomass of fungal or bacterial species added into autoclaved forest or arable soil was recovered by using this method. The microbial biomass measured by this method showed a good correspondence with that measured by the chloroform fumigation-extraction method. The fungal biomass in soils of the forest sites (55-107 g C m^<-2>, n=6) was larger than that in the soils of the arable sites (5.2-31 g C m^<-2>, n=5). The fungal biomass in the plots with various treatments in upland fields was as follows: 31 g C m^<-2> in the soil treated with manure and subjected to shallow tillage, 17 g C m^<-2> in the soil treated with manure and subjected to deep tillage, 12 g C m^<-2> in the soil treated with chemical fertilizers and subjected to shallow tillage, 8.7 g C m^<-2> in the soil treated with chemical fertilizers and subjected to deep tillage. Herbicide application did not affect the fungal biomass. On the other hand, the bacterial biomass in soils hardly differed among the forest (7.5-11 g C m^<-2>, n=6) and arable sites (5.0-9.2 g C m^<-2>, n=5), and that in the plots with various treatments in upland fields was almost identical (5.4-8.1 g C m^<-2>). The biomass ratios of fungi/bacteria of the forest sites (5.5-12) were higher than those of the arable sites (1.0-5.7). We also showed that the biomass ratios decreased with the decrease in the total microbial biomass.

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To examine the effect of a mulching sheet made of nonwoven fabric on the colonization of roots of weeping love grass, Eragrostis curvula (WLG), by arbuscular mycorrhizal (AM) fungi, both laboratory and field experiments were conducted. In the laboratory experiment, the effect of mulching on the growth of WLG was examined in combination with an AM fungal inoculum containing Gigaspora margarita and slow releasing chemical fertilizer under growth chamber conditions. After 35 days, growth enhancement of WLG was the largest in the mulching sheet treatment together with the inoculum and the fertilizer. In the field experiment, the effect of the mulching sheet was also examined in combination with the inoculum of two different AM fungi by using concrete framed fields. Mulching enhanced both the growth of WLG and fungal colonization in the case of both inocula after a growth period of 95 days. These results supported our previous findings showing that the use of the mulching sheet increased the effect of AM fungal inoculum on the rehabilitation of degraded soils.

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We compared the bacterial and fungal flora in the root zone of potato plants cultivated under Nature-Farming systems (NF) which are similar to organic farming systems, with those under conventional farming systems (CF). The fields under NF and CF were adjacent to each other in Mishima city, Shizuoka, Japan, and managed by different farmers. There was no appreciable difference between both systems in the number of aerobic bacteria and actinomyces in the potato roots and soils. The number of fluorescent Pseudomonas in the samples from NF was higher than that of CF. MIS (Microbial Identification System, MIDI Inc.) was used to identify the aerobic bacteria isolated from the roots. MIS indicated that the same bacterial species were isolated from both samples as the most abundant species. Based upon MIS analysis, the diversity of the root-colonizing bacteria of potato under NF was higher than that under CF. The bacteria showing an antifungal activity against a phytopathogen, Rhizoctonia solani, were isolated from the NF potato roots rather than from the CF roots. Comparison of the root fungal flora by the root-washing technique showed that Fusarium sp. and Trichoderma sp. were isolated from NF roots and CF roots, respectively, as the main fungi. The diversity of the root fungi under NF was higher than that under CF.

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A forty-five day incubation experiment was conducted under controlled laboratory conditions to study the interactive effects of elevated CO_2 concentration and temperature on the changes of the amount of microbial biomass nitrogen (N) and the mineralization of N in flooded paddy soil microcosms amended or not with rice straw. The microcosms with the two treatments were transferred separately to four growth chambers under different conditions of incubation and a 16 h/8 h light and dark regime. Two of the growth chambers provided a continuous flow of elevated CO_2 concentration (equivalent to 800 μl 1^<-1>), of which one was set at 25 ℃ and the other at 35 ℃. Similarly the other two growth chambers were run under near ambient CO_2 concentration (400 μl 1^<-1>) at each of the two temperatures. Replicates of microcosms were withdrawn from each of the growth chambers after 7, 15, 30 and 45 days of incubation and analysed for the contents of extractable N (E_n), microbial biomass N, ammonia and total N in surface (0-1 cm) and sub-surface (below 1 cm) soil layers. There was a significant difference between the amounts of E_n in the surface layers and sub-surface layers under all the conditions, the levels in the sub-surface soils being higher than those in the surface soils. The amount of microbial biomass N and total N content increased under elevated CO_2 concentration at the end of incubation compared with the ambient CO_2 concentration. The increase in total N content implied that the potential of biological N_2-fixation increased by elevated CO_2 concentration. N mineralization was enhanced by both elevated atmospheric CO_2 concentration and temperature in submerged rice soil without plants.

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Direct colony thin-layer-chromatography (TLC) was applied for the simple and rapid detection of strains producing antifungal substances. In this method, the bacterial colony was directly pasted onto the TLC plate and it was developed twice in the same direction with different solvents. For the detection of strains producing pyrrolnitrin (Pyr), a silica gel TLC plate pasted with the colonies of Pseudomonas fluorescens W8a grown on potato peptone glucose sucrose agar medium was developed firstly with methanol and secondly with a benzene-ethyl acetate mixture. When the plate was dried out and sprayed with Ehrlich's reagent, a clear red spot appeared at Rf=0.74. For 2,4-diacetylphloroglucinol (Phl), the plate pasted with colonies of P. fluorescens LRB3W1 cultured on malt extract agar medium was developed firstly with acetone and secondly with chloroform-methanol. A blue spot was detected on the plate at Rf=0.68 after spraying with Gibbs' reagent. This method was useful to detect the antibiotic-producing strains from wheat roots which were collected from fields continuously cultivated with wheat for a long period of time. This method can also be applied to select antibiotic-deficient strains among the transposon mediated mutants of P. fluorescens W8a.

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Physicochemical and microbial properties of five volcanic ash soils in Fukushima Pref., Japan, suppressive and conducive to Fusarium-wilt of radish, were investigated. Suppressive soils (S-soils) showed higher total C, total N, and nitrate contents, a higher cation exchange capacity (CEC), and a lower pH than conducive soils (C-soils). Germi-nation of microconidia of the pathogen was more suppressed in the S-soils than in the C-soils, suggesting that the S-soils displayed a higher fungistatic capacity. The numbers of total bacteria, culturable bacteria, total fungal propagules and indigenous Fusarium spp., were not clearly related to the disease incidence in the soils, whereas the ratio of actinomycetes to total culturable bacteria was higher in the S-soils than in the C-soils. The microbial community structure of the soils was examined based on the %G+C profiles of soil community DNA, phospholipid fatty acid analysis (PLFA), and community-level physiological profile (CLPP) using Biolog GN plates. There was no remarkable difference in the %G+C profiles between the C-soils and S-soils. PLFA and CLPP enabled to differentiate the community structure among the soils and suggested that the substrate utilization ability, estimated from the number of substrates utilized, and the ratio of Gram-positive bacteria, estimated from the proportion of branched fatty acids, were likely to be higher in the S-soils than in the C-soils. Microbial community structure specific to the soils suppressive to Fusarium-wilt of radish was analyzed by combining the results obtained by the different methods.

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In the soybean-Bradyrhizobium symbiosis, the initial stage of nodule formation is triggered by the release of the bacterial nod gene-inducing isoflavonoids from soybean plant. Analysis of the isoflavonoid contents in the seeds and root extracts of 12-day-old uninoculated soybean cultivars and their super/hypernodulating mutant using HPLC revealed that isoflavonoids daidzein, genistein, and coumestrol were present in the roots but only daidzein and genistein could be detected in the seeds. Moreover, all the super/hypernodulating soybean mutants showed lower isoflavonoid contents in the seeds and roots than their parent cultivars. These results suggest that in all the parent cultivars the genes which are probably responsible for controlling the isoflavonoid production are both affected during mutation despite the differences in the mutagen used and background of the seed materials.

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