In the process of mass flow through stomata, water output and CO 2 input are
coupled. Because solar radiation stimulates evapotranspiration through stomata
while also stimulating photosystems I and II, CO 2 must be absorbed to drive the
Calvin cycle, which consumes high-energy compounds such ATP and NADPH.
Thus, water evapotranspiration and CO 2 are fundamentally coupled. This watercarbon coupling is expressed as the water-use efficiency (WUE). The WUE is
slightly different among plant species, especially C3 and C4 plants and fast-growing
and slow-growing trees. However, as the main tree species in the tropical peatland
forest is a C3 plant and slow growth occurs in tropical peatlands, the WUE is
assumed to be
1 g CH 2 O by 500g 0:5 l
ð
ÞH 2 O ¼ 1 t CH 2 O=ha=year by 500 k=H 2 O
½
,
where CH 2 O is the abbreviation for carbohydrates.
Maurel and Nacry (2020) proposed that a comprehensive understanding of root
architecture and hydraulics (adjusting the root water transport capacity) as a whole
(root hydraulic architecture) is needed to understand the strategies used by plants to
optimize water uptake and to potentially improve crops with regard to this crucial
trait. Because roots continually adjust their hydraulics locally and globally on shorter
time scales, and because the mechanisms that directly underlie root growth and
development as well as tissue hydraulics are being uncovered, the signaling mechanisms that govern local and systemic root system adjustments as a function of water
availability remain largely unknown.
Maurel and Nacry (2020) also proposed a model for root architecture and
hydraulics that relies on the identification of novel genes involved in the regulation
of root hydraulics under composite stress conditions. Flooding results in oxygen
deficiency (hypoxia) in the root system. In the presence of nutrients (K
+
), the
induction of the HCR1 (hydraulic conductivity of root 1: gene) pathway enhances
the core anaerobic transcriptional response (anaerobic metabolism) and inhibits
water uptake. When roots are soaked in water without an O2 supply, the HCR1
pathway is upregulated.
In peatlands, root architecture adaptations, such as aerial roots and mound roots,
are extremely important. The functional differentiation of roots is also important,
such as main roots for water absorption in deep peat sites and lateral roots for O 2 and
nutrient absorption on land surfaces.
1.11 Conclusion
The peatland formation process is one of the keys for understanding peatland
characteristics. As proposed, peatland formation is categorized into two types:
(1) dome-type peatlands around the maritime continent in Southeast Asia and
(2) cuvette-type peatlands around the main rivers of the Amazon and the Congo
Basin. In dome-type peatlands, water is supplied almost entirely from rain,
1 Basic Information About Tropical Peatland Ecosystems
51
coupled. Because solar radiation stimulates evapotranspiration through stomata
while also stimulating photosystems I and II, CO 2 must be absorbed to drive the
Calvin cycle, which consumes high-energy compounds such ATP and NADPH.
Thus, water evapotranspiration and CO 2 are fundamentally coupled. This watercarbon coupling is expressed as the water-use efficiency (WUE). The WUE is
slightly different among plant species, especially C3 and C4 plants and fast-growing
and slow-growing trees. However, as the main tree species in the tropical peatland
forest is a C3 plant and slow growth occurs in tropical peatlands, the WUE is
assumed to be
1 g CH 2 O by 500g 0:5 l
ð
ÞH 2 O ¼ 1 t CH 2 O=ha=year by 500 k=H 2 O
½
,
where CH 2 O is the abbreviation for carbohydrates.
Maurel and Nacry (2020) proposed that a comprehensive understanding of root
architecture and hydraulics (adjusting the root water transport capacity) as a whole
(root hydraulic architecture) is needed to understand the strategies used by plants to
optimize water uptake and to potentially improve crops with regard to this crucial
trait. Because roots continually adjust their hydraulics locally and globally on shorter
time scales, and because the mechanisms that directly underlie root growth and
development as well as tissue hydraulics are being uncovered, the signaling mechanisms that govern local and systemic root system adjustments as a function of water
availability remain largely unknown.
Maurel and Nacry (2020) also proposed a model for root architecture and
hydraulics that relies on the identification of novel genes involved in the regulation
of root hydraulics under composite stress conditions. Flooding results in oxygen
deficiency (hypoxia) in the root system. In the presence of nutrients (K
+
), the
induction of the HCR1 (hydraulic conductivity of root 1: gene) pathway enhances
the core anaerobic transcriptional response (anaerobic metabolism) and inhibits
water uptake. When roots are soaked in water without an O2 supply, the HCR1
pathway is upregulated.
In peatlands, root architecture adaptations, such as aerial roots and mound roots,
are extremely important. The functional differentiation of roots is also important,
such as main roots for water absorption in deep peat sites and lateral roots for O 2 and
nutrient absorption on land surfaces.
1.11 Conclusion
The peatland formation process is one of the keys for understanding peatland
characteristics. As proposed, peatland formation is categorized into two types:
(1) dome-type peatlands around the maritime continent in Southeast Asia and
(2) cuvette-type peatlands around the main rivers of the Amazon and the Congo
Basin. In dome-type peatlands, water is supplied almost entirely from rain,
1 Basic Information About Tropical Peatland Ecosystems
51