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 31P nuclear magnetic resonance (NMR) spectroscopy to characterize the form of P and its distribution in undisturbed perhumid Chamaecyparis 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 (Po) contents in all studied soils decreased with soil depth. In addition, Po content was negatively correlated with soil crystalline Fe oxide content, whereas inorganic P (Pi) content was positively correlated with soil crystalline Fe oxide content and slightly increased with soil depth. Thus, Pi may be mostly adsorbed by soil crystalline Fe oxides in the soils. Among all extractable P fractions, the NaOH-Po fraction appeared to be the major component, followed by NaHCO3-Po; the resin-P and HCl-Pi fractions were lowest. In addition, we found no typical trend for Pi and Po contents in soils with topographical change among the three sites. From the 31P-NMR spectra, the dominant Po form in soils from all study sites was monoesters with similar spectra. The 31P-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

“…Phosphonate is produced by bacteria (e.g., Bacillus cereus) via enzymatic activity; however, bacteria are uncommon in acidic soil [23,34,43]. Thus, phosphonate was not detected in our sand dune forest soils.…”

“…Additionally, the content of P was similar in the humic and mineral-I layers. The plant litter was decomposed via biological cycling, so a great quantity of Po accumulated in soil surfaces [23]. NaOH-Po is mineralized slowly [2,41], which explained the large amount of NaOH-Po in the sand dune soils.…”

“…Phosphorus distribution and forms are influenced by changes in soil oxidation-reduction along a toposequence [23]. We hypothesized that P distribution and forms are affected by different topographies (upland and lowland) in a sand dune under varied soil conditions and biogeochemical processes.…”

Sequestration of P fractions in the soils of an incipient ferralisation chronosequence on a humid tropical volcanic island

“…Total content of P (P t ) is higher in the topsoils than in the diagnostic subsoil horizons (Table 3 ), probably due to biotic recycling (Shiau et al 2018 ). Total P values rise again with depth in some saprolitic C horizon.…”

“…Even where N and cationic nutrients are important, they are often co-determinants with P (Baillie et al 1987 ; Wright et al 2011 ). P is relatively stable in most soils, and can even accumulate in the organic layers of some forest soils, such as in humid subtropical subalpine Taiwan (Shiau et al 2018 ; Wu and Chen 2005 ). However, prolonged and intense weathering, leaching and erosion generally deplete P stocks, although slowly in most cases (Vitousek 2004 ).…”