diameter, i.e. lower root mass and slower growth in peat soil consisting of organic
matters and less nutritive salts will be observed in comparison with those in alluvial
mineral soil. The root mass of sago palm in peat soils and alluvial soils was also
discussed by Miyazaki (2015a). The mass decreased at greater distances from the
tree trunk center in alluvial mineral soils, but this tendency was not observed in peat
soils (Kasuya 1996). However, Tie et al. (1987) reported that the root system in peat
soils is denser and larger than that in mineral soils. The former reports expressed
different tendencies when the comparison was conducted to root growth between
sago palms grown in peat and mineral soils. Miyazaki et al. (2016) suggested that the
difference of varieties has more influential than that of regions and soil types.
Okazaki and Kimura (2015) expressed that the sago palm develops its root system
primarily in the soil layer of 0–30 cm below ground both in peat and mineral soils.
Miyazaki et al. (2011) reported that the root dry weight increases with the progress of
palm aging, with increasing horizontally before the trunk formation stage, while
after trunk formation roots increase vertically as aging progressed and expand
downwards. Kasuya (1996) surveyed the root mass in 8-year-old sago palm from
soil surface to 40 cm soil depth, and reported that thin roots smaller than 5 mm in
diameter were predominant in a shallow soil with 0–20 cm soil depth, while thick
roots greater than 5 mm in diameter were predominant in a deep soil with 20–40 cm
soil depth. Miyazaki et al. (2011) stated that root characteristics in sago palm might
be greatly influenced by the soil environment.
Yamamoto (1997) observed a well-developed lysigenous aerenchyma in both
thick and fine roots. Nitta et al. (2002) and Nitta and Matsuda (2005) mentioned
about physiological functions of sago palm roots especially in high water conditions.
This lysigenous aerenchyma provides sago palms with a water stress adaptation
mechanism (Okazaki 2015). Plants that have some forms of moisture tolerance
mechanism with water stress exclusion mechanisms (Fig. 17.3) are called as hydrophytes or helophytes (Shimoda 2005). The thick roots that develop from the surface
of the trunk are adventitious roots which penetrate deep into the soil directly below
the trunk (Fig. 17.4) (Nitta et al. 2002). The lateral roots elongate downward or
obliquely downward in mineral soils and deep peat soils, but can also be found
growing upward in especially deep peat soils (Fig. 17.5). This kind of upright
elongation and exposure of lateral roots to the air is often observed in the areas of
submerged or wet soils, and these roots act as aerial roots, taking in and feeding air to
the plant body as in the case of mangroves (Nitta 2015). Secondary lateral roots with
1–2 mm in diameter emerge in some cases.
The adventitious root and the lateral root are both comprising, from the outermost
layer to the center of epidermis, exodermis, suberized and thickened sclerenchyma,
cortex, and stele (Nitta 2015). Vascular bundles run inside the stele and consist of
xylem containing vessels and phloem containing sieve tubes. In both types of roots,
the cortex is made up of schizogenous aerenchyma, i.e. the intercellular space
created by the separation of adjoining cell walls as the plant grows, and lysigenous
aerenchyma, i.e. the intercellular space created by the loss of adjoining tissue cells as
the plant grows (Nitta 2015). The tissues noted above develop an aeration function
and adapt to growth under submerged conditions (Nitta et al. 2002). As a response to
484
H. Ehara et al.
matters and less nutritive salts will be observed in comparison with those in alluvial
mineral soil. The root mass of sago palm in peat soils and alluvial soils was also
discussed by Miyazaki (2015a). The mass decreased at greater distances from the
tree trunk center in alluvial mineral soils, but this tendency was not observed in peat
soils (Kasuya 1996). However, Tie et al. (1987) reported that the root system in peat
soils is denser and larger than that in mineral soils. The former reports expressed
different tendencies when the comparison was conducted to root growth between
sago palms grown in peat and mineral soils. Miyazaki et al. (2016) suggested that the
difference of varieties has more influential than that of regions and soil types.
Okazaki and Kimura (2015) expressed that the sago palm develops its root system
primarily in the soil layer of 0–30 cm below ground both in peat and mineral soils.
Miyazaki et al. (2011) reported that the root dry weight increases with the progress of
palm aging, with increasing horizontally before the trunk formation stage, while
after trunk formation roots increase vertically as aging progressed and expand
downwards. Kasuya (1996) surveyed the root mass in 8-year-old sago palm from
soil surface to 40 cm soil depth, and reported that thin roots smaller than 5 mm in
diameter were predominant in a shallow soil with 0–20 cm soil depth, while thick
roots greater than 5 mm in diameter were predominant in a deep soil with 20–40 cm
soil depth. Miyazaki et al. (2011) stated that root characteristics in sago palm might
be greatly influenced by the soil environment.
Yamamoto (1997) observed a well-developed lysigenous aerenchyma in both
thick and fine roots. Nitta et al. (2002) and Nitta and Matsuda (2005) mentioned
about physiological functions of sago palm roots especially in high water conditions.
This lysigenous aerenchyma provides sago palms with a water stress adaptation
mechanism (Okazaki 2015). Plants that have some forms of moisture tolerance
mechanism with water stress exclusion mechanisms (Fig. 17.3) are called as hydrophytes or helophytes (Shimoda 2005). The thick roots that develop from the surface
of the trunk are adventitious roots which penetrate deep into the soil directly below
the trunk (Fig. 17.4) (Nitta et al. 2002). The lateral roots elongate downward or
obliquely downward in mineral soils and deep peat soils, but can also be found
growing upward in especially deep peat soils (Fig. 17.5). This kind of upright
elongation and exposure of lateral roots to the air is often observed in the areas of
submerged or wet soils, and these roots act as aerial roots, taking in and feeding air to
the plant body as in the case of mangroves (Nitta 2015). Secondary lateral roots with
1–2 mm in diameter emerge in some cases.
The adventitious root and the lateral root are both comprising, from the outermost
layer to the center of epidermis, exodermis, suberized and thickened sclerenchyma,
cortex, and stele (Nitta 2015). Vascular bundles run inside the stele and consist of
xylem containing vessels and phloem containing sieve tubes. In both types of roots,
the cortex is made up of schizogenous aerenchyma, i.e. the intercellular space
created by the separation of adjoining cell walls as the plant grows, and lysigenous
aerenchyma, i.e. the intercellular space created by the loss of adjoining tissue cells as
the plant grows (Nitta 2015). The tissues noted above develop an aeration function
and adapt to growth under submerged conditions (Nitta et al. 2002). As a response to
484
H. Ehara et al.