坂本 一憲

千葉大学森林環境園芸(利根高冷地)農場内の果樹園(TNO-5)および林地(TNF-3)の土壌断面および微生物特性,ガス生成,含有微量元素を2003年9月に調査した結果,以下のことが明らかになった.1.無機態窒素,可溶性有機態炭素・可溶性全窒素はTNF-3>TNO-5となり,これらは埋没腐植層の付近で高くなる傾向を示した.2.微生物バイオマス,呼吸量は表層ではTNF-3>TNO-5となり,下層ほど減少する傾向が認められたが,埋没腐植層の付近(2Bw,4Bw)で再び増加する傾向が見出された.3.TNO-5における銅含量と,TNF-3における銅含量には大差が見られなかった.4.両地点とも亜鉛,銅,ヒ素含量は日本の平均値より低い値を示し,セレン含量は日本の平均値に近い値であった.

The external hypha of arbuscular mycorrhizal (AM) fungi, extending from roots out into soil, is an important structure in the uptake of phosphate from the depletion zone around each root. In this paper, we analysed some phospholipid fatty acids (PLFAs) derived from external hyphae of four AM fungi (Glomus etunicatum, Glomus clarum, Gigaspora margarita and Gigaspora rosea) to find fatty acids which may be useful as specific markers for identifying and quantify the external hyphae of Gigaspora species. Leek (Allium porrum L.) seedlings inoculated with each AM fungus were grown in river sand. Sand samples were collected and four PLFAs (16:1omega5, 18:1omega9, 20:1omega9 and 20:4) in the sand were analysed. In addition, the hyphal biomass in the sand was determined by the direct microscopic method. PLFAs 18:1omega9 and 20:4 were found in all the AM-inoculated and non-inoculated sand samples. PLFA 16:1omega5 was detected in the sand inoculated with G. etunicatum, G. clarum and Gi. rosea. PLFA 20:1omega9 was detected only in the sand inoculated with Gi. rosea. PLFAs 16:1omega5 and 20:1omega9 were not found in the sand inoculated with Gi. margarita. The amount of PLFA 20:1omega9 was closely correlated with the amount of biomass of external hyphae of Gi. rosea (r = 0.937, P < 0.001), whereas no correlation was observed for PLFA 16:1omega5. The 20:1omega9 content of Gi. rosea was approximately 6.56 nmol mg(-1) hyphal biomass. We suggest that PLFA 20:1omega9 can be used as a specific marker for identifying and quantifying the external hyphae of Gi. rosea, at least in controlled experimental systems. (C) 2004 Elsevier Ltd. All rights reserved.

千葉大学森林環境園芸(利根高冷地)農場内の果樹園および林地の土壌断面および理化学性・生物性を調査した結果,以下のようなことが示された.1.土壌層位は森林のほうが果樹園よりA層が厚かった.2.物理性では,果樹園Ap層で固相率が高く,B2層で未風化軽石の混入により低下していた.pF-水分曲線は,Ap,A,B2層ともに粗孔隙に土壌水が多量に保持されていた.飽和透水係数は,1.1×10^<-3>(Ap層)から5.6×10^<-3>(B1層)であり,透水性は良好であった.3.化学性では,森林土壌のほうが果樹園よりpHが低く,両地点ともに下層へいくに従ってpHが上昇するという傾向が見られた.全炭素,全窒素は両地点ともに下層ほど減少するという傾向がみられ,地点別では果樹園土壌>奉林土壌であった.無機態窒素も同様な傾向を示した.果樹園の位置で比べると斜面の中部で硝酸態窒素の高い傾向が見られた.4.果樹園現場での二酸化炭素フラックスは,2002年11月24日に316mgCO_2m^<-2>h^<-1>,2003年4月21日に219mgCO_2m^<-2>h^<-1>であった.室内培養による二酸化炭素生成量は斜面下部で最も大きく,次いで斜面中部≒上部,森林であった.亜酸化窒素生成量も同様な結果にならた.5.果樹園土壌の微生物バイオマス炭素,窒素はともに斜面中部≒上部>下部となった.林地土壌でのバイオマス炭素・窒素は果樹園土壌の上中部と同じ程度の値を示した.

To evaluate spatial variability of nitrous oxide (N2O) emissions and to elucidate their determining factors on a field-scale basis, N2O fluxes and various soil properties were evaluated in a 100- x 100-m onion (Allium cepa L.) field. Nitrous oxide fluxes were determined by a closed chamber method from the one-hundred 10- x 10-m plots. Physical (e.g., bulk density and water content), chemical (e.g., total N and pH), and biological (e.g., microbial biomass C and N) properties were determined from surface soil samples (0-0.1 m) of each plot. Geostatistical analysis was performed to examine spatial variability of both N2O fluxes and soil properties. Multivariate analysis was also conducted to elucidate relationships between soil properties and observed fluxes. Nitrous oxide fluxes were highly variable (average 331 mug N m(-2) h(-1), CV 217%) and were log-normally distributed. Log-transformed N2O fluxes had moderate spatial dependence with a range of &gt;75 m. High N2O fluxes were observed at sites with relatively low elevation. Multivariate analysis indicated that an organic matter factor and a pH factor of the principal component analysis were the main soil-related determining factors of log-transformed N2O fluxes. By combining multivariate analysis with geostatistics, a map of predicted N2O fluxes closely matched the spatial pattern of measured fluxes. The regression equation based on the soil properties explained 56% of the spatially structured variation of the log-transformed N2O fluxes. Site-specific management to regulate organic matter content and water status of a soil could be a promising means of reducing N2O emissions from agricultural fields.

A field experiment was conducted to determine N2O concentrations in the soil profile and emissions as influenced by the application of N fertilizers and manure in a typical Japanese Andisol, which had been under a rotation of oat and carrot for the previous 3 years. The treatments include ammonium sulphate (AS). controlled-re lease fertilizer (CRF) and cattle manure (CM) in addition to a control; all the fertilizers were applied either at 150 kg N ha(-1) or 300 kg N ha(-1) at the time of sowing carrot. NO emissions from the soil surface were measured with closed-chamber techniques. while N2O concentrations in the soil profile were measured using stainless steel sampling probes inserted into the soil at depths of 10, 20. 40, 60, 80 and 100 cm. Moreover. soil water potential, soil temperature and rainfall data were also recorded. The results indicated that N2O concentrations in the soil profile were always greater than in the atmosphere, ranging from 0.36 mul N2O-N 1(-1) to 5.3 mul N2O-N l(-1). The relatively large accumulation of N2O in the lower profiles may be a significant source for N2O flux. Taking the changes of soil mineral N into consideration, most emissions of NO were probably produced from nitrification. The accumulation of NO in the soil profile and emissions to the atmosphere were differently influenced by the amendments of N fertilizers and manure. being consistently higher in CRF than in CM and AS treatments at the corresponding application rates, but no significant difference existed with respect to the various N sources.

To determine the effect of sewage sludge compost and chemical fertilizer application on the soil chemical properties, net N mineralization rates, CO2 evolution rates, microbial biomass C and N, a non-leaching experiment was conducted under controlled conditions of temperature (25degreesC) and moisture content (80% WHC) using 2 types of soils that had been previously treated with sewage sludge composts or chemical fertilizer during short or long periods of time. The incubation lasted for 90 d. The treatments included: soils samples taken from 3 plots, each receiving sewage sludge compost with rice husk (RH), sewage sludge compost with sawdust (SD), and chemical fertilizer (CF), each applied at the rate of 200 kg N ha(-1) biannually for 22 years (Tama farm) and 2 years (Chiba farm). The application of SD and RH led to a significant increase in the total N and C and soluble organic C reservoirs of the two soil types regardless of the application history. Soil pH was always higher in the sludge-treated soils than in the CF-treated soils. The SD- and RH-treated soils at the Tama farm showed significantly higher emission rates of CO2, cumulative CO2, and microbial biomass C and N than the CF-treated soils and SD- and RH-treated soils at the Chiba farm. The metabolic quotients of the soils treated with sewage sludge compost were significantly higher than those of the CF-treated soils. However the soils treated with sewage sludge compost of both Tama and Chiba farms exhibited a mixed response during the incubation period. Net N mineralization rates were significantly higher in the soils treated with SD followed by RH at the Tama farm; while the SD, RH, and CF-treated soils of the Chiba farm and CF soils of the Tama farm exhibited a negative N mineralization rate (immobilization). These results showed that the soils amended with sewage sludge composts displayed larger and more active microbial biomass than those treated with CF, which has implications for current interests in shifting from chemical fertilizer application to organic wastes for promoting efficient nutrient cycling in agro-ecosystems.

The contribution of the hyphae of an arbuscular mycorrhizal (AM) fungus to the uptake of trace elements by marigold ( Tagetes patula L,) was studied using a multitracer consisting of radionuclides of Be-7, Na-22, Sc-46, Cr-51, Mn-54, Fe-59, Co-56, Zn-65, Se-75, Rb-83, Sr-85, Y-88, Zr-88, and Tc-95m. Marigold plants colonized and not colonized with Glomus etunicatum were grown for 40 and 60 d in pots with a hyphal compartment separated from the rooting medium by a fine nylon mesh. The multitracer was applied to the hyphal compartment, We found that the uptake of Na-22, Zn-65, Se-75, Rb-83, Sr-85, and Y-88 by the mycorrhizal plants was higher than that by the non-mycorrhizal ones. In the case of Tc-95m, the uptake by the mycorrhizal plants was similar to that by the control ones. The radioactivity of Be-7, Sc-46, Cr-51, Mn-54, Fe-59, Co-56, and Zr-88 could not be detected in any plants. Our results suggest that the AM fungus can absorb Na, Zn, Se, Rb, Sr, and Y from the soil and transport these elements to the plant through its hyphae, The transport ability of the AM fungal hyphae to plant for Be, Sc, Cr, Mn, Fe, Co, Zr, and Tc is likely to be low.

希土類元素（La、Sm、Yb）が植物の発芽とAM形成に及ぼす影響について検討した。また、希土類元素の添加とAM形成がマリーゴールドの生育に及ぼす影響についても検討した。その結果、次のことが明らかになった。 1)La、Sm、Ybが植物の発芽に及ぼす影響をマリーゴールド、タマネギ、トールフェスクの発芽種子の根長を比較することによって検討した。その結果、100μmolkg-1のLa、Sm、Ybを添加した培土では、全ての植物の根長は著しく減少した。一方、10μmolkg-1のLa、Sm、Ybの添加によってマリーゴールドの根長は減少しなかったが、タマネギとトールフェスクの根長はそれぞれYbあるいはSmの添加によって減少した。このため、発芽を阻害するLa、Sm、Ybの添加量は10ないし100μmolkg-1であると考えられた。 2)La、Sm、YbがAM形成に及ぼす影響をAM菌(Glomus etunicatum)を接種したマリーゴールドを用いて検討した。その結果、菌根形成率は10μmolkg-1のLa、Sm、Ybの添加によって影響を受けないことが明らかとなった。 3)AM形成とLa、Sm、Ybの添加が植物生育に及ぼす影響を2)と同様にAM菌(Glomus etunicatum)を接種したマリーゴールドを用いて検討した。マリーゴールドは10μmolkg-1のLa、Sm、Ybを添加した培土で栽培した。その結果、AM菌を接種しないマリーゴールドは地上部新鮮重がLaまたはYbの添加によって低下した。また、根部の新鮮重もYbの添加によって低下した。しかし、AM菌を接種したマリーゴールドの地上部新鮮重はLa、Sm、Yb添加の影響を受けなかった。このため、AM形成はLaやYbの添加によるマリーゴールドの生育の低下を軽減すると考えられた。

Twelve nodulation mutants (seven non-nodulating and five supernodulating) of soybean [Glycine max (L.) Mirr.] were screened for arbuscular mycorrhizal colonization in the presence of either Glomus etunicatum Becker and Gerdemann or Gigaspora margarita Becker and Hall. The cultivars showed variation in colonization parameters. The two supernodulating mutants En6500 and NOD1-3 had higher frequencies of colonization with 2.5-4.5 times higher arbuscular abundance than the respective wild types. The enhanced mycorrhization resulted in significant enhancement of P uptake by En6500. The non-nodulating mutants showed decreases in mycorrhizal parameters. Mutants En1282 and Harosoy exhibited aborted infection after formation of typical appressorium-like structures at some sites. However, none of these had the non-mycorrhizal phenotype. Growth and nutrient-uptake parameters should be considered while studying plant mutants for mycorrhization.

The effect of arbuscular mycorrhizal (AM) colonization on the uptake of trace elements in marigold (Tagetes patula L,) was studied using a multitracer consisting of radionuclides of Be-7, Na-22, Sc-46, Cr-51, Mn-54, Fe-59, Co-56, Zn-65, As-74, Se-75, Rb-83, Sr-85, Y-88, Zr-88, and (TC)-T-95m, Marigold plants were grown under controlled environmental conditions in sand culture either without mycorrhizas or in association with an AM fungus, Glomus etunicatum, The multitracer was applied to the pot, and plants were harvested at 7 and 21 d after tracer application. We found that the uptake of Be-7, Na-22, Cr-51, Fe-59, Zn-65, and Tc-95m was higher in the mycorrhizal marigolds than in the non-mycorrhizal ones, while that of Sc-46, Co-56, Rb-83, and S-85, was lower in the mycorrhizal marigolds than in the non-mycorrhizal ones. Thus, the multitracer technique enabled to analyze the uptake of various elements by plant simultaneously. It is suggested that this technique could be used to analyze the effects of AM colonization on the uptake of trace elements by plant.

We investigated the turnover time of microbial biomass-C in Japanese upland soils with various textures and examined the soil physicochemical properties influencing their turnover time. Samples from five different soil types (sand-dune regosol, light-colored Andosol, humic Andosol, brown forest soil, and dark red soil) were taken from upland concrete-frame plots in the experimental field of Chiba University. Each soil amended with [U-C-13] glucose was incubated for 80 d at 25 degrees C. Microbial biomass-C and -C-13 in soil were periodically determined by the fumigation-extraction method. The longest turnover time of microbial biomass-C was observed in the dark red soil (215 d) followed by the humic Andosol (134 d), brown forest soil (97 d), and light-colored Andosol (83 d) and the shortest in the sand-dune regosol (45 d). The turnover time of microbial biomass-C was significant;ly correlated with the value of soil clay (R: 0.917*), CEC (R: 0.921*), and macroaggregate (R: 0.907*) contents, but not with the total-C content;. The amount; of microbial biomass-C showed a close correlation with the turnover time of microbial biomass-C, suggesting that the turnover time of microbial biomass-C is an important factor influencing the accumulation of microbial biomass-C in soil.

Laboratory incubation was conducted to determine the controlling factors affecting the production of N2O in soil taken from short- and long-term experimental sites continuously amended with SS in three types of soil samples. Soil types and sludge application rates significantly affected the production of N2O from soil amended with sludge compost. The yellow soil, with low organic matter content, resulted in higher production of N2O with sewage sludge application probably due to ammonium oxidation in the soil. While andosol soil, with high organic matter content and heavy metal (Zn), resulted in lower N2O production when amended with SS. Uncultivated brown forest soil amended with sewage sludge plus sawdust compost (SSS) at the rate of 20 ton ha-1 showed a peak of N2O production, while no N2O was observed in the same soil at 10 ton ha-1 application rate. These results help us to explain that N2O production from soil amended with SS is greatly affected by soil types, types and application rate of the composts. It should be considered carefully to reduce N2O emission from the recycling of nutrient between soil/agriculture and urban/water treatments in future. (C) 2000 Elsevier Science Ltd.

Microbial biomass C and N, dehydrogenase and nitrifying activities were measured together with other physicochemical parameters of soil such as the three phase distributions, and the amounts of soil organic matter, mineralizable carbon and nitrogen, in a 100 cm deep Andosol profile in an arable field in Matsudo city, central Japan. In the three phase distributions of soil, the solid phase was: 5-10 cm = 15-20 cm&gt 55-60 cm &gt 35-40 cm = 75-80 cm. Total organic C and N were highest at 15-20 cm (40.4 and 2.8 mg kg-1, respectively) and decreased with depth, being lowest at 75-80 cm (18.6 and 0.6 mg kg-1, respectively). Available P and ammonium N followed the same trend as total organic C and N. However, nitrate N was highest at 35-40 cm (51.6 mg kg-1 soil) and lowest at 5-10 cm (19.1 mg kg-1 soil). Microbial biomass C and N were highest at 15-20 cm (202 and 26 mg kg-1 soil, respectively), and showed a tendency to decrease with depth. Mineralizable C and N followed the same trend as microbial biomass C and N and were found to have the lowest values at 75-80 cm. Dehydrogenase activity was highest at 15-20 cm and much lower below this depth (51.2 and 3.3-3.7 μg Triphenyl formazan g-1 soil 24 hr-1, respectively) and was highly correlated with soil microbial biomass (r2 = 0.922, P&lt 0.05). Nitrifying activity was also highest at 15-20 cm and decreased with depth to a low at 75-80 cm. These properties are important to understanding N dynamics in an Andosol profile, especially the mechanism of nitrate leaching from an arable field to ground water. © 2000, Japanese Society of Microbial Ecology – The Japanese Society of Soil Microbiology. All rights reserved.

Specific inhibitor and substrate specificity of alkaline phosphatase in the arbuscule of Glomus etunicatum were investigated, and the possible role of this enzyme in the symbiosis was discussed. Mycorrhizal roots of marigold (Tagetes patula) were digested by cellulase and pectinase to separate the intraradical hyphae from the root tissue, and phosphatase activity was stained at pH 8.5 and 5.0. The activity of alkaline phosphatase (pH 8.5) in arbuscules was inhibited in the presence of beryllium, whereas that of acid phosphatase (pH 5.0) was less sensitive to beryllium. Specificity and effectiveness of beryllium on the alkaline phosphatase was further confirmed using fractionated (soluble and insoluble) enzyme prepared from the separated hyphae. The soluble and insoluble alkaline phosphatases hydrolyzed phosphomonoester compounds (glucose-6-phosphate, beta-glycerophosphate, trehalose-6-phosphate and glucose 1-phosphate) but not pyrophosphate compounds (ATP and polyphosphate) which were hydrolyzed by acid phosphatase efficiently. The insoluble alkaline phosphatase showed high specific activity (on a protein basis) and high sensitivity to beryllium. Kinetic analysis of the insoluble alkaline phosphatase suggested the involvement of this enzyme in the sugar metabolism of the fungus due to lower Km values for sugar phosphate such as glucose-6-phosphate and trehalose-6-phosphate.

We investigated the effect of arbuscular mycorrhizal colonization (AMC) on ammonium-N uptake in the symbiotic system of marigold (Tagetes patula L.) and Glomus etunicatum (Becker and Gerd). Marigolds were cultivated in pots with five treatments at different P and N application levels with or without AMC. After growing the plants for 29 d, ^<15>N-ammonium-N was applied to each treatment. Twenty-four hours after ^<15>N-ammonium-N feeding, the plants were sampled for analysis. To evaluate the ammonium-N uptake activity of plant root, we determined the specific absorption rate of ammonium-N (SAR-AN : gN kg^<-1> root dry weight d^<-1>). The results obtained were summarized as follows : 1) At low P and N application levels, AMC increased the plant P concentration and decreased the plant N concentration. 2) The SAR-AN of marigold declined with the increase in plant P concentration due to AMC. The SAR-AN also declined with the increase in plant dry weight. However, the SAR-AN increased with the increase in plant N concentration. 3) The ^<15>N translocation from root to shoot was depressed due to AMC.

クロロホルムくん蒸抽出法を用いたバイオマス窒素量の迅速測定法を確立するために,可溶性全窒素量の測定にペルオキソ二硫酸カリウム分解法を用いた場合の換算係数について検討した。実験では15点の畑土壌におけるくん蒸土壌および非くん蒸土壌の可溶性全窒素量をケルダール法とペルオキソ二硫酸カリウム分解法とで測定し,両法で得られた窒素量の比較を行なった。その結果,ケルダール法とペルオキソ二硫酸カリウム分解法で得られたくん蒸土壌および非くん蒸土壌の可溶性窒素量はほぼ一致し,E_N値も高い相関関係を示した。従ってペルオキソ二硫酸カリウム分解法はバイオマス窒素の迅速かつ正確な測定法として有効であると考えられ,この方法を使用した場合の換算係数としては,2.41が適当であると考えられた。しかしながら,ケルダール法によって定量されたE_N値が低い土壌試料(<9.0mgN kg^<-1>乾土)や可溶性全窒素量が高い土壌試料(>200mgN kg^<-1>乾土)の一部には換算係数が2.41を大きく外れる場合が認められた。可溶性全窒素量が高い試料は希釈して測定することが望ましいと考えられた。

Grass straw and leaf mix (GL) were composted in-vessel with and without seeding material. Changes in pH, CO2-evolution rate (CER), and the microbial biomass in terms of total extractable lipid phosphate (TELP) contents were monitored until 150 d, The microbial biomass contents were nearly stabilized at about 0.11 mmol TELP kg(-1) DM from the 60th day onward. The CER decreased gradually with the progression of composting and became stable also from the 60th day onward at around 1 g CO2-C kg(-1) DM d(-1). On the contrary, the pH increased gradually until the 40th day and then became stabilized at about 8.8 during the remaining period of composting. The characteristics of the GL composts (150 d) were compared with those from other ready-composts. The germination indices (GI) of Dia sorghum seeds showed that all the composts were biologically mature. Although the pH varied from compost to compost, microbial biomass of GL and incubated ready-composts was about 0.1 mmol TELP kg(-1) DM. Similarly, CER did not exceed a maximum value of 1.2 g CO2-C kg(-1) DM d(-1), Significant positive effects of seeding material addition were detected in total organic carbon and organic matter contents of GL composts, Ho Never, the effect of the addition of a seeding material was not obvious in the case of the microbial biomass and CER measurements. The results show that the germination index and CER together can give sufficiently reliable information about the maturity of GL composts, although the validity of our results for large-scale open field composting needs to be examined further.

The response of peanut (Arachis hypogaea L.) to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus etunicatum) and Bradyrhizobium sp. was studied in pots by the acetylene reduction activity (ARA) and 'A-value' methods. The soil used was a Light-coloured Andosol and the treatments consisted of the inoculation of VAM fungi only, inoculation of Bradyrhizobium, only, dual inoculation of VAM fungi and Bradyrhizobium and control, under non-sterilized and sterilized soil conditions. In the non-sterilized soil the ARA and nitrogen fixation determined by the 'A-value' method increased significantly only by dual inoculation of VAM fungi and Bradyrhizobium at 100 days after planting (DAP), but no significant difference was observed at 70 DAP. In the case of dual inoculation, 75% of the nitrogen of the plant was derived from fixation whereas the plants inoculated only with Bradyrhizobium derived 68% of their nitrogen from fixation and the control plants, 64%, Amount of P in plant increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium. In the sterilized soil a highly significant increase in the ARA was observed of the dual inoculation at all the sampling times. Nitrogen fixation determined by the A-value technique and N and P contents in plant also increased significantly by dual inoculation, Results obtained by the A-value method showed that plants with dual inoculation derived 68% of their nitrogen from fixation while the plants inoculated only with Bradyrhizobium, 38%. From our this study we conclude that nitrogen fixation as well as N and P contents in peanut increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium.

第13回日本土壌肥料学会奨励賞受賞業績

We carried out an experiment to investigate the contribution of microbial biomass N to soil N which was made available by soil heating treatment, and was analyzed by an ^<15>N-labelled technique. The soils used were Dark red soils and Andosols collected from Chiba prefecture. After labelling the microbial biomass N with ^<15>N, the soils were heated (50,100,150℃) and fumigated. The mineralized N and ^<15>N were measured at 0,10,and 20 days after incubation. In both soils, the amount of N mineralized from the heated soil increased with the increase in the temperature of heating treatment. However, the ^<15>N abundance of the N mineralized from the heated soil decreased with it. The ^<15>N abundance of the N mineralized from the heated soil at 50℃ and from the fumigated soil was approximately equal to that of the ^<15>N-labelled microbial biomass. Based on these results, we suggest that the N mineralized from the heated soil at 50℃ is mainly derived from the microbial biomass N, and that the ratio of the contribution of non-biomass N to the mineralized N increases with the temperature of heating treatment.

The relationship between the fungal:bacterial biomass ratio and the metabolic quotient (qCO(2)) was studied in three different soils. In addition, the effect of the fungal:bacterial biomass ratio on the relationship between CO2 evolution and the size of the soil microbial biomass was examined. Soil samples were collected from three experimental fields amended with various organic materials (Yatsugatake, Ibaraki, and Tochigi fields). The range of the fungal:bacterial biomass ratio in the Yatsugatake and Ibaraki fields was small (1.54-2.24 and 1.11-1.71, respectively), but it was large in the Tochigi field (1.18-3.75). We found a high negative correlation between this ratio and the metabolic quotient (qCO(2)=2.10-0.361 (fungal:bacterial biomass ratio), R=-0.851, P&lt;0.01) in the Tochigi field. Therefore, we suggest that qCO(2) decreases with an increase in the fungal:bacterial biomass ratio, which may be due to a higher efficiency of substrate C use by fungal flora in comparison with bacterial flora. In the Yatsugatake and Ibaraki fields, there was a high positive correlation between CO2 evolution and total microbial biomass. In contrast, no correlation was observed between these two parameters in the Tochigi field, probably reflecting the wide range of values for the fungal:bacterial biomass ratio. From the results obtained, we suggest that the fungal:bacterial biomass ratio is an important factor regulating the relationship between CO, evolution and the size of the microbial biomass.

We carried out an experiment to compare the amounts of carbon and nitrogen mineralized by chloroform fumigation and heating (50, 100, 150, and 200°C) in order to clarify the origin of the carbon and nitrogen mineralized by the drying treatment, for the development of a soil fertility index. The amount of carbon mineralized from the fumigated soil was approximately equal to that from the soil heated at 50°C. The amount of nitrogen mineralized from the fumigated soil was equal to that from the soil heated at 50 and 100°C. The decrease in the number of bacteria in the fumigated soil was approximately equal to that in the soil heated at 50°C. On the other hand, the decrease in the number of actinomycetes and fungi in the fumigated soil was equal to that in the soil heated at 100°C. Based on these results, we suggest that the carbon and nitrogen mineralized in the soil heated at 50 and 100°C were mainly derived from the biomass fraction and at above 100°C, mainly from the non-biomass fraction. © 1992, Japanese Society of Soil Science and Plant Nutrition. All rights reserved.

The relationship between the amount of organic material applied and soil biomass content was examined in soils amended with various organic materials in 4 upland experimental fields. The values of the soil biomass measured by the direct microscopic method (DMM), ATP content, and soil respiration rate in the soil amended with organic material were greater than those in the soil amended with inorganic fertilizer in all the fields. Soil biomass measured by the DMM and ATP content were highly correlated with the sum of the amount of hot water-soluble organic substance, carbohydrate, and crude protein components in the organic material applied in all the fields. Soil respiration rate was also highly correlated with the sum of the amount of these components applied in the 3 fields. These results suggest that hot water-soluble organic substance, carbohydrate, and crude protein components in organic material are closely related to the increase of the soil biomass. The difference in the soil biomass C content calculated from the ATP content among the 4 fields generally paralleled the difference in the soil total C content. The ratio of biomass C to the total C in the field with a high total C content was lower than that in the field with a low total C content. The rates of increase of the soil biomass measured by the DMM, ATP content, and soil respiration rate in the field with short-term application of organic material were higher than those in the field with long-term application. These findings suggest that the rate of increase of the soil biomass is high when the duration of application of organic material is short.