林木落葉の分解に関与する土壌糸状菌について

Abstract

(1) 京都市近郊の林地糸状菌の種類, 概数及び季節的変動を求め, さらにアカマツ落葉の分解は主としてどのような土壤糸状菌によつて行われているかについて条件を変えて調査し, 同時にまたこれら糸状菌の有機物分解力について調べた｡ (2) 京都市近郊のアカマツ, アカシデ, スギ, ヒノキ林で分離された糸状菌は27属に達した｡ 季節的には本実験の範囲内で一般に春季に最大で秋季に最小となる傾向があり, また土壤層別にはAo層に最も多く下層程糸状菌数は減少した｡ これらの試験区を通じて比較的普遍的に認められたものはRhizopus, Trichoderma, Aspergillus, Penicillium, Acrostalagmusの5属であり, この他アカマツ林にはMucor, Cunninghamella, Chaetocladium, Mortierella (?), Oospora, Cephalosporium, Monosporium (?), Torulaなどが認められた｡ なお鞍馬スギ林, ヒノキ林では糸状菌の数が少なかつたのみでなくその種類も少なく, Penicilliumが著しく大きな割合を占めた｡ (3) アカマツ落葉の分解に関与する主な糸状菌はMucor, Penicillium, Trichodermaの3属でありこの他Aspergillus, Paecilomycesも条件によつては優勢となつた｡ 糸状菌の種類, 数はアカマツ落葉の分解が行われるときの条件によつて変化するが, 水分条件は種類を変化せしめるよりも数量的に著しい変化をおこし, 養分, 酸度条件は種類をも変化せしめる｡ 水分条件のみを変えるといづれの場合にもPenicillium waksmani, Penicillium decumbensが優勢となり, これらは実騒期間 (80日間) を経過しても減少する傾向はなく相当永続的にアカマツ落葉の分解に関与するようである｡ Mucor hiemalis (?) は200% ~ 300%の水分条件でのみあらわれ, Trichoderma koningiは水分の比較的少ないときにあらわれた｡ 酸度を変えると弱酸性区 (pH 6.27 ~ 6.20) と対照区 (pH 3.81 ~ 4.89) ではPenicilliumの3種, すなわち P. decumbens, P. waksmani, P. steckii (?) が優勢となり, 酸性区 (pH 4.54 ~ 5.34) では Paecilomyces sp., Penicillium roqueforti (?), Penicillium restrictumが優勢となりMucor hiemalis (?), Trichoderma koningiがこれについだ｡ 強酸性区 (pH 4.22 ~ 4.92) でもPaecilomyces sp., Penicillium restrictumがあらわれ, この他Aspergillus fumigatusも同時に優勢となつた｡ いづれの場合も接種後約1週間経過すると糸状菌の種類が当初の接種材料中のそれに比べ著しく減少したが, 一方糸状菌数は約1ケ月後に最大となつた｡ (4) これら糸状菌のセルローズ分解力をCO2発生量を指標としてCのmgで示すとSoil Emulsion (30日間) 216.65, Penicillium decumbens (28日間) 134.19, Penicillium steckii (?) (30日間) 70.09, Trichoderma koningi (28日間) 68.66, Aspergillus fumigatus (30日間) 61.89, Penicillium waksmani (28日間) 40.99でありPaecilomyces sp. は14日間で7.06mgにすぎなかつた｡ この他Mucor hiemalis (?), Penicillium restrictum, Penicillium citreo-viride (?) もPaecilomyces sp. と同様セルローズ分解力は極めて微弱であるかまたは全くその能力をもたないと考えられた｡ なお分解の速さは糸状菌によつて異なるようで, Trichoderma koningi はCO2発生量の最大が8日目にあらわれ最もはやかつたに対しPenicillium decumbens, Penicillium waksmaniはいづれも20日目に, Penicillium steckii (?), Aspergillus fumigatusは28日目に漸く最大を示した｡ すなわちCO2発生量で示される分解の全量とセルローズの上に生育する早さとは必ずしも一致しなかつた｡ アカマツ落葉から単離したリグニンの分解力をPhoma hibernica, Aspergillus versicoior, Penicillium aculeatum, Pullularia pululans, Torula alii, Paecilomyces sp. について調べると, いづれも微弱でリグニン分解の能力があつたとはいえないようである｡

This report deals with a study of the flora and the activity of the forest soil fungi. (I) The decompositions-rate of forest litter influences greatly the humification processes and soil fungi play an important role in decomposition, so the fungous flora of forest soil has an important relation to forest soil fertility. On the other hand, the decompositions-rate of forest litter is influenced by climatic and edaphic conditions, and fungous flora is also varied by same conditions. Therefore, the relation between the decomposition of forest litter and the decomposing fungous flora is very complex. In order to make this relation clear the following experiments were made; (a) about the fungous flora, its seasonal and its soil horizontal variations of some forest soils near Kyoto-city, (b) about the typical fungi that decompose Akamatsu litter under various nutrients contents (N. P. K. Mg. Ca), various moisture contents (100%, 200%, 300%, 400%) and various acidity of Akamatsu litter, (c) about the decomposing ability of the soil fungi with cellulose and lignin. (II) The numbers of genus of soil fungi was 27, that were isolated from soils of Akamatsu (Pinus densiflora S. et Z.), Akaside (Carpinus laxiflora Blume.), Sugi (Cryptomeria japonica D. Don) and Hinoki (Chamaecyparis obtusa S. et Z.) forest. It was found by this experiments that the maximum number of soil fungi exists in spring, and minimum in autumn, and the highest in Ao layer and decreased with the depth of soil layer. The most common fungi in test forest soils were Rhizopus, Trichoderma, Aspergillus, Penicillium and Acrostalagmus. In addition to them, Mucor, Cunninghamella, Chaetocladium, Mortierella (?), Oospora, Cephalosporium, Monosporium (?) and Torula were found in Akamatsu forest. The isolated fungi in Sugi and Hinoki forest were few in number and in genus, and Pinicillium was dominant among them. (III) When Akamatsu litter was decomposed, the most common decomposing fungi were Mucor, Penicillium and Trichoderma, and in some special conditions, Aspergillus and Paecilomyces were also found. (i. e., they were found in all conditions tested.) When the Akamatsu litter was decomposed under the 100, 200, 300 and 400% (% of litter weight) moisture contents, Penicillium decumbens and Penicillium waksmani were found in all test conditions, and they did not decrease at the end of the experiment period (80 days), therefore, they decompose the Akamatsu litter during a considerable long time. Mucor hiemalia (?) was found only at 200 and 300% moisture content, Trichoderma koningi under drier condition. When the Akamatsu litter was decomposed under various acid conditions, the species of the typical decomposing fungi varied with the grade of acidity. The grades of acidity were following 4 conditions; (1) weak acid (pH. 6.27 ~ 6.20) (2) acid (pH. 4.54 ~ 5.34) (3) strong acid (pH. 4.22 ~ 4.92) (4) control (pH. 3.81 ~ 4.89). The typical fungi found on these conditions were following; (1) weak acid----Penicillium decumbens, Penicillium waksmani, Penicillium steckii (?); (2) acid----Paecilomyces sp., Penicillium roqueforti (?), Penicillium restricutum and Mucor hiemalis (?), Trichoderma koningi, followed them; (3) strong acid----Paecilomyces sp., Penicillium restricutum, Aspergillus fumigatus; (4) control----Penicillium decumbens, Penicillium waksmani, Penicillium steckii (?). Therefore, it seemed that the decomposing fungous flora were scarecely influenced in species, but greatly in number by moisture conditions. The nutrients contents and the acidity varied also the species greatly. The decomposing fungus flora varied with incubating period. Over about a week, the number of the species of the decomposing fungi decresse compared with those of inoculating material. On the other hand, the maximum number of fungi was found after about a month. (IV) The cellulose decomposing ability of these fungi were following (CO2 evolution as C mg.): Soil Emulsion (30 days) 216.65 mg. Penicillium decumbens (28 days) 134.19 mg. Penicillium steckii (?) (30 days) 70.09 mg. Trichoderma koningi (28 days) 68.66 mg. Aspergillus fumigatus (30 days) 61.99 mg. Penicillium waksmani (28 days) 40.89 mg. Paecilomyces sp. (14 days) 7.06 mg. It seems that cellulose decomposing ability of Mucor hiemalis (?), Penicillium. restricutum and Penicillium. citreo-viride (?) was as poor as Paecilomyces sp.. The decomposingrate of cellulose was different with the species of fungi. Trichoderma koningi grew most rapidly on cellulose and its maximum CO2 evolution was found on the 8th day. On the other hand, Penicillium decumbens and Penicillium waksmani on 20 th day, Penicillium steckii(?), Aspergillusfumigatus on the 28 th day; i. e., the total amount of the decomposed cellulose indicated by CO2 evolution had not always relation with the rapidity grew on cellulose. It seemed that lignin decomposing ability of test fungi was always poor or not existed The test fungi were following; Phoma hibernica, Aspergillus versicolor, Penicillium aculeatum, Pullularia pullulans, Torula alii Paecilomyces sp..