Most soils derived from volcanic ash and pumice show distinctive properties that are not found in soils derived from other parent materials under the same vegetation and climate. Thorp and Smith (1949) first recognized them as a great soil group and gave them the tentative name Ando soils; Ando means dark soils in Japanese. They noted a wide distribution of these soils in deposits of volcanic ash not only in Japan but in other parts of the world. The Ando soils consist, primarily, of dark brown to black A1 horizons, averaging about 30 cm thick, of fine crumb or granular structure with the organic content close to 8% on average and ranging up to 30% in the darkest members of the group. Some members of the group have distinct B horizons with more clay than A horizons, but the younger members are essentially AC soils. The soils have low exchangeable “bases” and occur in humid to perhumid climates with temperature efficiency ranging from cool mesothermal to tropical. Natural vegetation varies from place to place and includes broad-leaved and coniferous forest types often with an understory of bamboo. Thorp and Smith (1949) had some difficulty in deciding whether Ando soils should be placed in the zonal or intrazonal orders, because they did not know whether the dark color of the soils was caused by vegetation or by the soils’ parent material.

The Distinctive Properties of Andosols

In the rhizosphere, phosphorus (P) levels are low because of P uptake into the roots. Rhizobacteria live on carbon (C) exuded from roots, and may contribute to plant nutrition by liberating P from organic compounds such as phytates. We isolated over 300 phytate (Na-inositol hexa-phosphate; Na-IHP)-utilizing bacterial strains from the rhizosheath and the rhizoplane of Lupinus albus (L.). Almost all of the isolates were classified as Burkholderia based on 16S rDNA sequence analysis. Rhizosheath isolates cultured with Na-IHP as the only source of C and P showed lower P uptake at the same extracellular phytase activity than rhizoplane strains, suggesting that bacteria from the rhizosheath utilized phytate as a C source. Many isolates also utilized insoluble phytate (Al-IHP and/or Fe-IHP). In co-culture with Lotus japonicus seedlings, some isolates promoted plant growth significantly.

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Plant growth promotion abilities and microscale bacterial dynamics in the rhizosphere of Lupin analysed by phytate utilization ability

This paper reviews the major steps which have contributed to our knowledge of rhizosphere biology since 1904. The progress made has been very considerable, and the frustrations limited. Prospects are bright for improving our understanding of the biology of the rhizosphere and for managing the rhizosphere microflora to increase plant growth.

Rhizosphere research - 85 years of progress and frustration

Microbial diversity, numbers, and metabolic activities in Minnesota peatlands were investigated using a variety of microbial enrichment and enumeration procedures together with radioisotopic measurements of microbial degradative processes. Minnesota peatlands were shown to contain large microbial populations of wide metabolic diversity. Direct counts of bacteria using epifluorescence microscopy indicated bacterial populations of about 10(8) ml(-1) of peatland water, irrespective of depth. Radioisotopic most-probable-number (MPN) counts of heterotrophs able to mineralize(14)C-labeled substrates to(14)CO2 showed significant populations of glucose degraders (10(4)-10(6) ml(-1)) as well as degraders of benzoate (10(2)-10(3) ml(-1)), 2,4-dichlorophenoxyacetate (10(2)-10(5) ml(-1)), and sphagnum (10(3)-10(7) ml(-1)) in the various peatlands examined. The MPNs of NO3 (-) reducers varied from 10(3)-10(6) ml(-1), SO4 (-) reducers from 10(2)-10(3) ml(-1), methanogenic bacteria from 10(3)-10(6) ml(-1), and methane oxidizers from 10(3)-10(4) ml(-1), depending on sampling site and depth. Eighty pure cultures of aerobic bacteria and fungi were isolated from Minnesota peats. Most of those cultures tested were able to grow on at least 20 organic compounds (carbohydrates, aromatic molecules, hydrocarbons, etc.) as sole sources of carbon and energy. One isolate, aBacillus, was able to fix atmospheric N2. Several of the isolates were able to mineralize(14)C-labeled lignin.

Microbial diversity of Minnesota peatlands.

More than 90% of the rice fields in Asia are cultivated with the soil submerged during most of the growth period. Wetland rice fields are of three types: irrigated, shallow-water rain fed, and deep-water rain fed. Management practices in an irrigated rice field include: (1) leveling the land and constructing levees to impound water; (2) puddling of wet soil; (3) maintenance of 5–10 cm of standing water during rice growth; (4) draining and drying at harvest of rice; and (5) re-flooding after an interval of from a few weeks to as long as 8 months. In shallow-water rain-fed fields, the soil is submerged as in the irrigated fields, but the rice crop is frequently subjected to drought or to flooding deeper than the height of rice. In deep-water rice fields, the rice is sown on dry land before the onset of the monsoon, and the depth of the floodwater gradually increases as the rice grows, sometimes reaching 2-5 m. Near the harvest, the floodwater is gradually drained. Rain-fed rice fields in monsoon Asia may be subjected to severe desiccation during the dry season.

Microbial Ecology of Flooded Rice Soils

Introduction Many previous investigations, beginning with the observations of Hiltner19, have established the fact that soil in the rhizosphere contains a higher quantity of microorganisms than soil which is not within the influence of the plant root. It has been shown also that the balance between certain physiological groups4,21,43,45, as well as that between morphological types of bacteria or fungi30,50 is changed in the rhizosphere. In addition, Canadian investigators23,34,62) have reported a change in the balance of certain nutritional groups of soil bacteria in the rhizosphere. Two excellent reviews6,22) covering these papers have recently appeared. Since then a number of papers2,7,9,11,13,15-18,25,26,33,36,38-40,48,54,57-60,63) concerning various aspects of the microbial population of the rhizosphere have been published.

https://www.tandfonline.com/doi/pdf/10.1080/00380768.1957.10431904

Studies on microbial population in the rhizosphere of higher plants with special reference to the method of study

The microbiological characterization of Japanese soils has been one of main themes in the authors' laboratory, and it has been proved that volcanogenous soil is characterized by smaller number of bacteria and larger number of actinomycetes than non-volcanogenous soil (1) Such difference in microflora of both soil groups is considered to reflect the difference between the properties inherent in each soil As the next step, it seems quite reasonable to consider whether there exists qualitative difference in each group of microorganisms

Actinomycete flora of japanese soils:II. Seasonal Change of Actinomycete Flora; (A) On the Basis of Morphological and Cultural Characters

https://www.tandfonline.com/doi/pdf/10.1080/00380768.1969.10432788

ACTINOMYCETE FLORA OF JAPANESE SOILS : III. Actinomycete Flora of Paddy Soils : (A) On the Basis of Morphological, Cultural and Biochemical Characters

https://www.tandfonline.com/doi/pdf/10.1080/00380768.1969.10432804

ACTINOMYCETE FLORA OF JAPANESE SOILS : III. Actinomycete Flora of Paddy Soils : (B) On the Basis of Antibiotic Production

The nature of soil is modified differently depending upon the artificial condition such as its utilization or management. It is therefore expected that the microbiological characteristic of soil is changed also. Greaves1) and Williams2) reported that the reclamation of virgin soil brought about a change of bacterial count. Suzuki et al3) observed that the kind of fungi differed between a virgin and a cultivated soil and that the vegetative mycelium was numerous in the former than in the latter. On the other hand, according to W aksman and Starkey4), the bacterial count differed depending upon the fertility of soil. Singh5) reported also that the number of fungi and actinomycetes was higher in a fertile than in an infertile soil. Lochhead6), and Lochhead and Chasen studied the bacterial flora of a fertile (long-continued application of manure) and an infertile (no fertilizer for many years) soil and found that a certain difference could be observed when morphological, physiological and nutritional...

Tatsuhiko Suzuki

Papers

Studies on microbial population in the rhizosphere of higher plants with special reference to the method of study

Actinomycete flora of japanese soils:II. Seasonal Change of Actinomycete Flora; (A) On the Basis of Morphological and Cultural Characters

ACTINOMYCETE FLORA OF JAPANESE SOILS : III. Actinomycete Flora of Paddy Soils : (A) On the Basis of Morphological, Cultural and Biochemical Characters

ACTINOMYCETE FLORA OF JAPANESE SOILS : III. Actinomycete Flora of Paddy Soils : (B) On the Basis of Antibiotic Production

Studies on microörganisms and their activities in soil Part. 2. Virgin and cultivated soil of the same origin