Characterization of Phosphorus in a Toposequence of Subtropical Perhumid Forest Soils Facing a Subalpine Lake

Abstract

The productivity of forests is often considered to be limited by the availability of phosphorus (P). Knowledge of the role of organic and inorganic P in humid subtropical forest soils is lacking. In this study, we used chemical fractionation and 31 P nuclear magnetic resonance (NMR) spectroscopy to characterize the form of P and its distribution in undisturbed perhumid Taiwan false cypress (Chamaecyparis formosensis Matsum.) forest soils. The toposequence of transects was investigated for the humic layer from summit to footslope and lakeshore. The clay layer combined with a placic-like horizon in the subsoil may affect the distribution of soil P because both total P and organic P (P o) contents in all studied soils decreased with soil depth. In addition, P o content was negatively correlated with soil crystalline Fe oxide content, whereas inorganic P (P i) content was positively correlated with soil crystalline Fe oxide content and slightly increased with soil depth. Thus, P i may be mostly adsorbed by soil crystalline Fe oxides in the soils. Among all extractable P fractions, the NaOH-P o fraction appeared to be the major component, followed by NaHCO 3-P o ; the resin-P and HCl-P i fractions were lowest. In addition, we found no typical trend for P i and P o contents in soils with topographical change among the three sites. From the 31 P-NMR spectra, the dominant P o form in soils from all study sites was monoesters with similar spectra. The 31 P-NMR findings were basically consistent with those from chemical extraction. Soil formation processes may be the critical factor affecting the distribution of soil P. High precipitation and year-round high humidity may be important in the differentiation of the P species in this landscape.

Characterization of Phosphorus in Subtropical Coastal Sand Dune Forest Soils

“…The extraction procedure began with 0.5 g of air-dried soil. First, an anion exchange resin was applied to extract part of labile P i [24,27,32], then the remaining soil sample was extracted by applying 0.5 M NaHCO 3 , 0.1 M NaOH, and 1M HCl solutions sequentially. NaHCO 3 and NaOH were used to extract P, which was adsorptive to soil colloids [33] and combined strongly with Fe and Al [13].…”

“…The oxidation-reduction states of minerals (e.g., iron and aluminum) affect the distribution and forms of P in soils [8,9,27]. For instance, P i was bound with Fe oxides strongly in oxidation conditions [27], but P was released from Fe minerals into soil solution in reduction conditions [8].…”

“…The oxidation-reduction states of minerals (e.g., iron and aluminum) affect the distribution and forms of P in soils [8,9,27]. For instance, P i was bound with Fe oxides strongly in oxidation conditions [27], but P was released from Fe minerals into soil solution in reduction conditions [8]. In addition, phosphorus sorption was affected by variations in mineralogy between soil layers, with a low sorption in organic matter-enriched top layers and high sorption in sesquioxide-enriched deep layers [1,28].…”

“…Several studies have characterized the P dynamics and distributions through either chemical sequential extraction or 31 P-NMR spectroscopy in tropical forests [24][25][26], subtropical forests [27,28], and temperate forests [4,23]. Negassa and Leinweber [29] indicated that only a few studies have characterized P in soils by comparing 31 P-NMR and sequential chemical extraction.…”

Distribution Changes of Phosphorus in Soil–Plant Systems of Larch Plantations across the Chronosequence

“…The dynamic change of P is crucial to assess the growth and function of a forest. Further, it is closely related to the ability of soil to supply P, and the ability of plants to extract available P from the soil and to cycle absorbed P among different plant components [8][9][10]. Soil P exists in many chemical forms, including labile P and stable P forms in Hedley fractionation [11].…”