6.2.2 Characterization of Monosaccharide Composition by
Numerical Index
Several numerical indices have been used to characterize the composition of neutral
sacharides in relation to the relative abundance of plant-derived and microbe-derived
saccharides in soil, such as hexoses/pentoses, mannose/xylose, and the reverse of
these ratios. Here we use a molar ratio of galactose + mannose (GM) to arabinose +
xylose (AX), henceforth the GM/AX ratio, to infer the relative contributions of
microbe-derived and plant-derived saccharides in soil, with a larger ratio indicating a
greater contribution from microbe-derived saccharides (Oades 1984). The ratio is
calculated using molar quantities as hexose and pentose differ in molecular weight.
In addition, we follow Sugiura et al. (2017) who proposed that the EH-glucose/NEHglucose ratio could be also used as a numerical index to infer relative abundance of
plant-derived and microbe-derived polysaccharides in soil, with a larger ratio indicating a greater contribution from microbe-derived saccharides.
6.2.3 Statistical Analysis and Terminology
Statistical significant test on comparisons among different soil groups, different plant
species, and among different sugar components were conducted by Welch’s t-test
( p ¼ 0.05, unless otherwise noted) with Bonferroni correction for multiple groups,
and without for two groups. A term “sugar” is used as a synonym of neutral
monosaccharide.
6.3 Origins of Soil Polysaccharides
The contribution of specific organisms to the content and composition of saccharides
depends on the amount and continuity of the supply of saccharides from the
organism into soil. Persistence of saccharides in soil, irrespective of their sources,
is another significant factor affecting the extent of the contribution. Plant polysaccharides are decomposed in soil fairly quickly, but some portion are declined
very slowly (Sowden and Ivarson 1962; Murayama 1984a; Cheshire et al. 1988).
Polysaccharides in microbial biomass remains are recycled to microbial ones. Soil
animals such as earthworms and nematodes are also sources of soil polysaccharides.
However, most animals contain a much smaller proportion of their tissue in the form
of carbohydrate than do plants mainly because they do not have a rigid cell-wall
structure (Cheshire 1979). Saccharides of animal biomass remains, mucas and cast
might not be persistent in soil as microorganisms consume rapidly. We focus on
plant materials and microoriganisms as origin of soil polysaccharides.
6 Origin of Soil Polysaccharides, and Ectomycorrhizal Fungal Sclerotia as Sources . . .
95
Numerical Index
Several numerical indices have been used to characterize the composition of neutral
sacharides in relation to the relative abundance of plant-derived and microbe-derived
saccharides in soil, such as hexoses/pentoses, mannose/xylose, and the reverse of
these ratios. Here we use a molar ratio of galactose + mannose (GM) to arabinose +
xylose (AX), henceforth the GM/AX ratio, to infer the relative contributions of
microbe-derived and plant-derived saccharides in soil, with a larger ratio indicating a
greater contribution from microbe-derived saccharides (Oades 1984). The ratio is
calculated using molar quantities as hexose and pentose differ in molecular weight.
In addition, we follow Sugiura et al. (2017) who proposed that the EH-glucose/NEHglucose ratio could be also used as a numerical index to infer relative abundance of
plant-derived and microbe-derived polysaccharides in soil, with a larger ratio indicating a greater contribution from microbe-derived saccharides.
6.2.3 Statistical Analysis and Terminology
Statistical significant test on comparisons among different soil groups, different plant
species, and among different sugar components were conducted by Welch’s t-test
( p ¼ 0.05, unless otherwise noted) with Bonferroni correction for multiple groups,
and without for two groups. A term “sugar” is used as a synonym of neutral
monosaccharide.
6.3 Origins of Soil Polysaccharides
The contribution of specific organisms to the content and composition of saccharides
depends on the amount and continuity of the supply of saccharides from the
organism into soil. Persistence of saccharides in soil, irrespective of their sources,
is another significant factor affecting the extent of the contribution. Plant polysaccharides are decomposed in soil fairly quickly, but some portion are declined
very slowly (Sowden and Ivarson 1962; Murayama 1984a; Cheshire et al. 1988).
Polysaccharides in microbial biomass remains are recycled to microbial ones. Soil
animals such as earthworms and nematodes are also sources of soil polysaccharides.
However, most animals contain a much smaller proportion of their tissue in the form
of carbohydrate than do plants mainly because they do not have a rigid cell-wall
structure (Cheshire 1979). Saccharides of animal biomass remains, mucas and cast
might not be persistent in soil as microorganisms consume rapidly. We focus on
plant materials and microoriganisms as origin of soil polysaccharides.
6 Origin of Soil Polysaccharides, and Ectomycorrhizal Fungal Sclerotia as Sources . . .
95