Takuya Marumoto

Inoculation with arbuscular mycorrhizal fungi: the status quo in Japan and the future prospects

Inoculation of arbuscular mycorrhizal (AM) fungi has potential benefits in not only sustainable crop production but also environmental conservation. However, the difficulty of inoculum production due to the obligate biotrophic nature of AM fungi has been the biggest obstacle to putting inoculation into practice. Nevertheless, several companies have sought to produce inoculum of AM fungi. Firstly in this review, the present status of inoculum production and its use in Japan is described. Secondly, although the effectiveness of inoculation is primarily limited by environmental and biological factors, some possible ways to improve inoculation performance are discussed. Approaches include use of chemicals to increase spore germination and colonization and soil application of charcoal to provide a microhabitat for AM fungi to colonize and survive.

Mineralization of C and N from microbial biomass in paddy soil

SummarySoil samples of paddy fields with different fertilizer managements in Yamaguchi Agricultural Experiment Station, Japan were used to investigate the contribution of microbial biomass to the pool of mobile plant nutrients in paddy soil. The quantities of nutrients mobilized in soils which had been fumigated or dried were closely related to the quantities available in freshly killed biomass. A “KN-factor” (28 days) of 0.24 for the proportion of total N mineralized from dead biomass in paddy soils was obtained. It was observed that the C to N ratio mineralized from freshly killed biomass by chloroform fumigation of paddy soils was nearly 10 under aerobic conditions. For an approximate calculation of biomass C from the flush-N by chloroform fumigation of paddy soils, the equations of (B=33 Fn, 10 days) and (B=26 Fn, 28 days) were indicated. In oven-dried (70°C, 24 h) and rewetted soils, about 66% of N was mineralized from the freshly killed biomass during 28 days of incubation and the remaining 34% was derived from non-biomass organic matter of paddy soils.

Drying effect on mineralizations of microbial cells and their cell walls in soil and contribution of microbial cell walls as a source of decomposable soil organic matter due to drying

Abstract 1) The mineralization of several kinds of microbial cells added to soil were accelerated considerably by the drying effect. 2) When microbial cells were roughly divided by mechanical procedure into two parts, i.e., cytoplasmic and cell wall substances, and separately added to soil with or without drying previously, the former was mineralized very quickly both with and without drying previously and its mineralization was not accelerated by the drying effect. The latter without drying previously was mineralized rather slowly, and the latter with drying previously was mineralized very quickly and remarkably. Furthermore, the former with and without drying previously left hardly any residual matter in soil, but the latter without drying previously left considerable residual matter because of making a complex resistant to microbial decomposition with colloid materials such as clay minerals and humus, and mineralization of the residual matter was remarkably accelerated by the drying effect. 3) From the...

Estimation of Microbial Biomass Carbon and Nitrogen in Bangladesh Soils

Abstract In order to estimate the microbial biomass content and to quantify the amount of available plant nutrients derived from microbial biomass in Bangladesh soils, biomass-C, -N, and available-N contents using samples from 8 soils were measured by applying the chloroform fumigation and drying-rewetting methods, respectively. 1) Contents of organic carbon and total nitrogen were 0.36-1.06 (av. 0.74) and 0.04-0.11 (av. 0.07)% in samples from eight soils collected in the central and north-eastern region of Bangladesh. 2) The contribution of biomass-C to soil organic carbon was about 2%, ranging from 1.35 to 3.32. The contribution was higher in grassland soil than in cropped arable soil with similar organic C contents. 3) The contribution of biomass-N to total soil nitrogen ranged from 1.15 to 2.95 (av. 2.11). 4) The average ratio of flush-C to fiush-N for a 10 day period of incubation was 7.02. 5) The contents of organic C, microbial biomass and available plant nutrients in the Bangladesh soils were sign...

Suppression of growth of Ralstonia solanacearum, tomato bacterial wilt agent, on/in tomato seedlings cultivated in a suppressive soil

Abstract To identify the sites responsible for the suppressiveness of tomato bacterial wilt in a suppressive soil, population dynamics of {iRalstonia solanacearum} in non-rhizosphere soil, roots and stems of tomato plants was compared between a wilt-conducive soil and a suppressive soil both of which were artificially infested with the pathogenic strain SL8. Rhizobacteria were recovered as two fractions; root fraction-l obtained after four washings in water, which was assumed to correspond to the rhizoplane, and root fraction-2 that was macerated after the washings and was assumed to be the fraction corresponding to the part inside of the roots and the firmly attached cells to the rhizoplane. In the conducive soil, all the tomato seedlings wilted while none wilted in the suppressive soil during the 3l-d period of cultivation after transplanting to soils infested with the pathogen at an initial density of 103 cfu per g dry soil. The number of pathogens in the conducive soil increased first in root fraction...

Mineralization and microbial biomass formation in upland soil amended with some tropical plant residues at different temperatures

Abstract A model experiment was carried out at 15, 25, and 35°C to investigate the changes in microbial biomass and the pattern of mineralization in upland soil during 8 weeks following the addition of 8 organic materials including 6 tropical plant residues, ipil ipil (Leucaena leucocephala), azolla (Azolla pinnata), water hyacinth (Eichhornia crassipes), dhaincha (Sesbania rostrata), cowpea (Vigna unguiculata), and sunhemp (Crotalaria juncea). The amounts of CO2-C evolved and inorganic N produced at 35°C were about 2 times larger than those at 15°C. At any temperature, the flush decomposition of C was observed within the first week and thereafter the rate of mineralization became relatively slow. A negative correlation was observed between inorganic N and C/N ratios of the added organic materials. The relationships between the amounts of cellulose or cellulose plus hemicellulose and the amount of mineralized N of the added organic materials were also negative. The changes in the microbial biomass were af...

Mineralization and changes in microbial biomass in water-saturated soil amended with some tropical plant residues

Abstract An incubation experiment was conducted in the laboratory at 25 and 35°C during 56 d to analyze the mineralization patterns and the changes in microbial biomass in water-saturated soils amended with 6 types of organic materials (O.M.) including residues from 4 tropical plants. C and N mineralization in amended and non-amended soils was influenced by the temperature, A significantly positive correlation was observed between C mineralization and the amount of hexoses of the amended O.M. regardless of the period of incubation. A negative relationship between the N mineralized from amended O.M. and C/N ratios and the amounts of cellulose plus hemicellulose of the added O.M. was observed during the period of maximum mineralization on the 49th day at 25°C. The critical C/N ratio value for N mineralization and immobilization was observed in dhaincha (15.7) and cowpea (22.0). The pattern of changes in microbial biomass C and N was almost similar at both 25 and 35°C. The amount of biomass C and N gradually...

Effect of peat on mycorrhizal colonization and effectiveness of the arbuscular mycorrhizal fungus Gigaspora margarita

Abstract The influence of the addition of Chinese peat and Canadian peat on arbuscular mycorrhizal colonization, mycorrhizal effectiveness and host-plant growth was investigated in a pot experiment. Chinese peat or Canadian peat was mixed with Masa soil (weathered granite soil) at different levels (0, 25, 50, 100, 150 or 200 g kg−1) into which an arbuscular mycorrhizal fungus (AMF) Gigaspora margarita Becker & Hall was inoculated, and seedlings of Miscanthus sinensis Anderess were planted. There was a significant increase in plant growth with increasing amounts of Chinese peat. The growth-promoting effect of the AMF on the host was enhanced when the addition of Chinese peat was increased from 25 to 100 g kg−1. Root colonization and the number of spores proliferating increased with increases at low levels of Chinese peat (from 25 to 100 g kg−1), and decreased gradually with higher Chinese peat increments. Although plant growth and root colonization with the addition of Canadian peat increased slightly, Canadian peat suppressed mycorrhizal effectiveness. In contrast to Canadian peat, the addition of Chinese peat improved considerably the physical and chemical properties of the soil, which might result in the promotion of AM formation and mycorrhizal effectiveness.

Stimulatory effect of peat on spore germination and hyphal growth of arbuscular mycorrhizal fungus Gigaspora margarita

Abstract The effects of peat extract solutions on spore germination and hyphal growth of the arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall were investigated. Spores were incubated in extract solutions of peat from China and peat moss from Canada, which were prepared at a weight ratio of 1:10, 1:20, 1:30, 1:50 and 1:100 for each substrate according to the weight ratio of water. Compared with peat and peat moss solutions, solutions of KH2PO4 and (NH4)2SO4 at various concentrations were used as media to investigate the effect of phosphorus (P) and nitrogen (N). Spores in the peat solutions showed the highest values for germination percentage, hyphal length and number of auxiliary cells, and these values were significantly higher than the values recorded for the other treatments. In contrast, in the peat moss extract solutions, which had a lower content of N and higher content of P than the peat solutions, the germination and hyphal growth of spores decreased. Spore growth was promoted with increased concentrations of the N solutions. However, P solutions exerted an inhibitory effect on spore germination and hyphal growth. Peat solutions showed a high N content and low P content, which might be related to the promotion of spore growth.

Estimation of mycorrhizal colonization of the roots of oak seedlings inoculated with an ectomycorrhizal fungus, Laccaria amethystea

Abstract Six-month-old seedlings of Quercus serrata and Quercus glauca in a nursery were inoculated with the ectomycorrhizal fungus Laccaria amethystea encapsulated in alginate gel and grown in the nursery. The seedlings were collected at 1, 3, and 5 months after the inoculation and examined for colonization of the root system with ectomycorrhizal fungi. The roots within 5 months after the inoculation showed rudimentary ectomycorrhizal colonization. The level of colonization of the root system was estimated based on the intensity of hyphal covering on the root tips by staining with a fluorescent dye and expressed as an index of mycorrhizal colonization (IMC). IMC increased with the time after inoculation and reached values of 4 and 12% in Q. serrata and Q. glauca, respectively at 5 months after the inoculation. The determination of IMC may enable to assess the development of mycorrhizal colonization of the root system that shows rudimentary ectomycorrhizas after the inoculation.