1.9.2 Phosphorus (P)
Phosphorus (P) is one of the major nutrients that especially limits vegetative growth
(Koerselman and Meuleman 1996; Verhoeven et al. 1996; Lambers et al. 1998;
Agren et al. 2012). P-deficient plants show delayed flower initiation, a decrease in
flower numbers and premature leaf senescence (Marschner 1995). In peat swamp
forests, the P nutrient content is very low due to the characteristics of the forests,
which are always flooded, causing peat forest soils to contain high levels of humic
acid. This results in the formation of organic metal complexes, which adsorb P and
render it unavailable for plants (Woolhouse 1981; Djuwansah 2000; Haraguchi et al.
2000). Based on several studies, the P content was recorded in the range of 272–340
in Central Kalimantan, and this value was lower than that in Riau, which was
approximately 500–900 mg g
À1 (Page et al. 1999; Suharjo and Widjaja-Adhi 1976).
1.9.2.1 Sources of Phosphorus
Phosphorus in peat forests comes from rainfall, stem flow, litter, and litter decomposition on the forest floor. The phosphorus content in rainfall originates from
several sources, such as biomass burning and wind erosion from peat soils tilled
during the dry season, lightning during the rainy season, and emissions from
phosphate mining activities during the dry and rainy seasons (Grimshaw and Dolske
2002). However, as tropical peatlands in Southeast Asia have a peat dome structure,
water is supplied from only rain, which is extremely low in nutrients. Thus, not only
phosphorus but also other nutrients have been applied at extremely low rates over the
past more than 1000 years, therefore, tropical peatlands are defined as extremely
nutrient-poor ecosystems.
The greatest amount of P is stored in aboveground biomass, followed by that in
litterfall. Approximately 25% of P is derived from aboveground biomass. Annual
litterfall also plays a major role in nutrient inputs in ecosystems, and the reproductive
part is one of the litterfall components that contributes the most P to the ecosystem
(Yustinus 2005). A study of the nutritional cycle in peat swamp forests in Central
Kalimantan found that the P input from aboveground biomass was between
36.1–64.75, that from belowground biomass was 1.5–4.2 kg ha
À1 year
À1 , and that
from litterfall and the litter on the forest floor was in the range of 0.06– 1.3 kg ha
À1
year
À1 , and 0.003–0.02 kg ha
À1 y
À1 , respectively.
The source of P nutrient inputs depends on the plant species composition. In
Central Kalimantan’s peat swamp forests, P nutrient inputs come from decomposed
dominant plant species. Some of these species rapidly release nutrients, such as
Buchanania sessilifolia Blume, and others are resistant and release P slowly, such as
Vatica oblongifolia Hook f. ssp. oblongifolia Ashton and Gluta rugulosa (Rahajoe
2003; Rahajoe and Kohyama 2003). For B. sessilifolia, P is released from its
decomposition in the first month after litterfall, then increases slowly in the second
month and is stable until the litter decomposes completely (Rahajoe 2003; Rahajoe
1 Basic Information About Tropical Peatland Ecosystems
41
Phosphorus (P) is one of the major nutrients that especially limits vegetative growth
(Koerselman and Meuleman 1996; Verhoeven et al. 1996; Lambers et al. 1998;
Agren et al. 2012). P-deficient plants show delayed flower initiation, a decrease in
flower numbers and premature leaf senescence (Marschner 1995). In peat swamp
forests, the P nutrient content is very low due to the characteristics of the forests,
which are always flooded, causing peat forest soils to contain high levels of humic
acid. This results in the formation of organic metal complexes, which adsorb P and
render it unavailable for plants (Woolhouse 1981; Djuwansah 2000; Haraguchi et al.
2000). Based on several studies, the P content was recorded in the range of 272–340
in Central Kalimantan, and this value was lower than that in Riau, which was
approximately 500–900 mg g
À1 (Page et al. 1999; Suharjo and Widjaja-Adhi 1976).
1.9.2.1 Sources of Phosphorus
Phosphorus in peat forests comes from rainfall, stem flow, litter, and litter decomposition on the forest floor. The phosphorus content in rainfall originates from
several sources, such as biomass burning and wind erosion from peat soils tilled
during the dry season, lightning during the rainy season, and emissions from
phosphate mining activities during the dry and rainy seasons (Grimshaw and Dolske
2002). However, as tropical peatlands in Southeast Asia have a peat dome structure,
water is supplied from only rain, which is extremely low in nutrients. Thus, not only
phosphorus but also other nutrients have been applied at extremely low rates over the
past more than 1000 years, therefore, tropical peatlands are defined as extremely
nutrient-poor ecosystems.
The greatest amount of P is stored in aboveground biomass, followed by that in
litterfall. Approximately 25% of P is derived from aboveground biomass. Annual
litterfall also plays a major role in nutrient inputs in ecosystems, and the reproductive
part is one of the litterfall components that contributes the most P to the ecosystem
(Yustinus 2005). A study of the nutritional cycle in peat swamp forests in Central
Kalimantan found that the P input from aboveground biomass was between
36.1–64.75, that from belowground biomass was 1.5–4.2 kg ha
À1 year
À1 , and that
from litterfall and the litter on the forest floor was in the range of 0.06– 1.3 kg ha
À1
year
À1 , and 0.003–0.02 kg ha
À1 y
À1 , respectively.
The source of P nutrient inputs depends on the plant species composition. In
Central Kalimantan’s peat swamp forests, P nutrient inputs come from decomposed
dominant plant species. Some of these species rapidly release nutrients, such as
Buchanania sessilifolia Blume, and others are resistant and release P slowly, such as
Vatica oblongifolia Hook f. ssp. oblongifolia Ashton and Gluta rugulosa (Rahajoe
2003; Rahajoe and Kohyama 2003). For B. sessilifolia, P is released from its
decomposition in the first month after litterfall, then increases slowly in the second
month and is stable until the litter decomposes completely (Rahajoe 2003; Rahajoe
1 Basic Information About Tropical Peatland Ecosystems
41