When expressed in logarithm, there can be a linear relationship between the size
(diameter, major axis) of various soil components or structures and the time required
for their formation or development. For instance, the development of macropores or
aggregates may require 1–10 years per 0.1–1 mm. Although the size of many
microscale constituents is known, the time required for formation is not well
known, such as formation of clay minerals, reaction of soil solution, or gas
exchange. Inorganic and organic complex is a well-known conceptual soil component. Soil chemistry and soil physical-chemistry will lead our further understanding
on soil microscale component and processes. We are just beginning to investigate
the mesoscale components in soil to deepen our knowledge on the complicated
reaction and heterogeneous substances in soil.
Mesoscale phenomenon comprises soil components that take several months to
years to form particles with a diameter of 1–10 mm. Iron and manganese nodules,
10 mm in diameter, formed under seasonal waterlogging condition in lowland soils
belong to this category. Soil aggregates, some formed by earthworms, may also
belong to mesoscale category in terms of their diameter, although time scale of
forming aggregates has not been sufficiently investigated. Formation of sclerotia,
0.1 mm in diameter, observed on agar plates within several weeks of inoculation
(Massicotte et al. 1992), may belong in the category of mesoscale components
as well.
According to such time and space definitions, mesoscopic component/phenomenon is visible in some cases with the aid of an optical microscope or magnifying
glass. Study of this category may require more biological approach than macro-scale
and microscale components/phenomena, which are investigated by pedological
approach and physical-chemical approach, respectively. Mesoscale components of
soil occupy a position at the intersection of various fields of investigation.
The following passage is partly taken from a foreword to an issue of a soil
physics’ journal (Nanjo 2018):
Soil is studied at a macro level in most places, including agriculture, and soil science needs
to be useful in macro situations. And so far, it seems that soil has been sampled macroscopically, and the macroscopic samples are crushed and homogenized for analysis and measurement. As a result, most of the soil phenomena treated as macro may have been described.
Given these circumstances, we propose development of a new method. How about returning
to the level of soil particles, reviewing the soil measurement method so far and proceeding
with visual inspection at the soil particle level?
Sclerotia grains in soil are visible with the naked eye. However, attempts to use
molecular methods to identify the fungi that produced the sclerotia grains are not
always successful. Our results suggest that the sclerotia are formed by species other
than Cenococcum geophilum, including related species of dark-septate-endophytes,
or that many of the sclerotia are degraded that DNA extraction is difficult. Trappe
(1969) differentiated “dead sclerotia” and “living sclerotia” by testing whether or not
they floated in water. However, Cenococcum sclerotia can act as a substrate for
diverse fungi (Obase et al. 2014) and persist in soil for a long time. As mentioned in
Chap. 4, Sphingomonas (currently Sphingobium) bacteria were isolated from sclerotia collected from Mt. Myoko, central Japan, with a
14 C age of ca. 1000 year BP,
210
M. Watanabe
(diameter, major axis) of various soil components or structures and the time required
for their formation or development. For instance, the development of macropores or
aggregates may require 1–10 years per 0.1–1 mm. Although the size of many
microscale constituents is known, the time required for formation is not well
known, such as formation of clay minerals, reaction of soil solution, or gas
exchange. Inorganic and organic complex is a well-known conceptual soil component. Soil chemistry and soil physical-chemistry will lead our further understanding
on soil microscale component and processes. We are just beginning to investigate
the mesoscale components in soil to deepen our knowledge on the complicated
reaction and heterogeneous substances in soil.
Mesoscale phenomenon comprises soil components that take several months to
years to form particles with a diameter of 1–10 mm. Iron and manganese nodules,
10 mm in diameter, formed under seasonal waterlogging condition in lowland soils
belong to this category. Soil aggregates, some formed by earthworms, may also
belong to mesoscale category in terms of their diameter, although time scale of
forming aggregates has not been sufficiently investigated. Formation of sclerotia,
0.1 mm in diameter, observed on agar plates within several weeks of inoculation
(Massicotte et al. 1992), may belong in the category of mesoscale components
as well.
According to such time and space definitions, mesoscopic component/phenomenon is visible in some cases with the aid of an optical microscope or magnifying
glass. Study of this category may require more biological approach than macro-scale
and microscale components/phenomena, which are investigated by pedological
approach and physical-chemical approach, respectively. Mesoscale components of
soil occupy a position at the intersection of various fields of investigation.
The following passage is partly taken from a foreword to an issue of a soil
physics’ journal (Nanjo 2018):
Soil is studied at a macro level in most places, including agriculture, and soil science needs
to be useful in macro situations. And so far, it seems that soil has been sampled macroscopically, and the macroscopic samples are crushed and homogenized for analysis and measurement. As a result, most of the soil phenomena treated as macro may have been described.
Given these circumstances, we propose development of a new method. How about returning
to the level of soil particles, reviewing the soil measurement method so far and proceeding
with visual inspection at the soil particle level?
Sclerotia grains in soil are visible with the naked eye. However, attempts to use
molecular methods to identify the fungi that produced the sclerotia grains are not
always successful. Our results suggest that the sclerotia are formed by species other
than Cenococcum geophilum, including related species of dark-septate-endophytes,
or that many of the sclerotia are degraded that DNA extraction is difficult. Trappe
(1969) differentiated “dead sclerotia” and “living sclerotia” by testing whether or not
they floated in water. However, Cenococcum sclerotia can act as a substrate for
diverse fungi (Obase et al. 2014) and persist in soil for a long time. As mentioned in
Chap. 4, Sphingomonas (currently Sphingobium) bacteria were isolated from sclerotia collected from Mt. Myoko, central Japan, with a
14 C age of ca. 1000 year BP,
210
M. Watanabe