To explore a possible phosphorus limitation of soil microbial processes, we fractionated phosphorus in Japanese forest soils (10 Inceptisols, three allophanic Andisols, seven nonallophanic Andisols, and one Spodosol) by sequential extraction into inorganic P (Pi) and organic P (Po) in H2O, 0.5 M NaHCO3, 0.1 M NaOH, 1 M HCl and conc. HCl fractions, and total P in residual fractions. NaOH-Pi and NaOH-Po fractions were the largest P components in all soil types. Apart from H2O-Pi, NaOH-Pi, and NaOH-Po, P concentration in each fraction did not differ significantly among soil types. Concentrations of P in fractions H2O-Pi, H2O-Po, 0.1 M NaOH-Pi, 0.1 M NaOH-Po, and residual P were correlated with active Al, but not with active Fe, indicating a more significant contribution of Al in controlling P forms in the soils. The proportion of available P (H2O + NaHCO3 − P) to total P was negatively affected by active Al and Fe contents and by pH in the soils. High phosphomonoesterase and phosphodiesterase are known to be indicators of low soil P availability, and both activities were higher in soils with low available P in this study, suggesting that microorganisms of these forest soils may be P limited.
1Department of Environmental Sciences, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Japan. Dr. Takashi Kunito is corresponding author. E-mail: firstname.lastname@example.org
2Nagano Vegetable and Ornamental Crops Experiment Station, 1066-1 Tokoo, Soga, Shiojiri, Japan.
3Soil Science and Plant Nutrition Division, NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Japan.
4Biotron Application Center, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, Japan.
Received July 1, 2011.
Accepted for publication September 13, 2011.
Financial Disclosures/Conflicts of Interest: Dr. Kunito received a Grant-in-Aid for Young Scientists (B) (No. 22710007) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors have no conflicts of interest to declare.