Nobuhiko Matsuyama

Acidification and soil productivity of allophanic Andosols affected by heavy application of fertilizers

The acidification of allophanic Andosols by fertilizer application in relation to soil productivity was studied with special reference to the soil colloidal composition. Among the Japanese cultivated allophanic Andosols, in 95% of the samples, the exchange acidity y 1 was < 6, while in 5% of the samples (30 soil samples) the exchange acidity y1 was ≧ 6. The strongly acidic allophanic Andosols (exchange acidity y 1≧ 6) did not significantly differ from the weakly acidic allophanic Andosols in the contents of amorphous materials. However, the mean values of the strongly acidic allophanic Andosols for the soil pH and base saturation which were 4.5 ± 0.3 and 15 ± 9%, respectively, were relatively lower than those of weakly acidic allophanic Andosols. The content of KCl-extractable Si in the strongly acidic allophanic Andosols dominated by allophane (exchange acidity y 1≧ 6 and allophane/clay content ratio > 0.7) ranged from 51 to 141 mg kg−1, and the values increased with increasing concentrations of KCl-extractable Al. KCl-extractable Al in the cultivated allophanic Andosols was considered to be derived from both the allophane fraction and Al-humus complexes. In the field studies of allophanic Andosols with successive application of fertilizers conducted at the Fujisaka Branch of Aomori Agricultural Experiment Station, the value of the exchange acidity y 1 of the topsoil and subsoil exceeded 6 about 40 and 50 years after the start of the experiment, respectively. The yield of flint corn (Zea mays L. var. indurata Bailey. cv. Onoa) in the fertilizer plot decreased by the strong soil acidification. The amount of nitrogen mineralized in the soil of the fertilizer plot during a 280-d incubation was 0.114 g kg−1 in the topsoil and 0.041 g kg−1 in the subsoil. These values were relatively low compared with those in the lime + fertilizer plot. Thus, we confirmed that the subsoil fertility of the fertilizer plot decreased by heavy application of fertilizers.

Characterization of cultivable methanotrophs from paddy soils and rice roots

Abstract Characterization of methanotrophs isolated from paddy soils and rice (Oryza sativa) roots was investigated in the present study. The number of methanotrophs in root homogenates of the rice cultivar Mutsuhomare was 4.9 × 107 most-probable-number (MPN) g−1 dry roots, in Yumeakari it was 2.0 × 108 MPN g−1 dry roots and in Kirara it was 4.6 × 107 MPN g−1 dry roots. Although bacterial cells were observed infrequently on the surface and in the interiors of roots before incubation, a large number of colonies, measuring 0.5–5 mm in diameter, were observed on the sterilized roots after incubation on nitrate mineral agar plates under methane in air. In particular, a large number of colonies were observed at the emergence sites of lateral roots and root hairs. Strains MD5-1 and M1 were isolated from the roots of Mutsuhomare and strain R62 was isolated from the root homogenate of Yumeakari. All isolates were catalase-positive and oxidase-positive, Gram-negative, straight-rod-shaped and curved-rod-shaped bacteria, and formed exospores. The isolates were able to fix nitrogen and grew in the absence of copper. In addition, all were found to be positive for naphthalene-oxidizing activities (corresponding to soluble methane mono-oxygenase activities). Strains MD5-1, M1 and R62 were closely related to Methylosinus sporium. Methanotrophic strains W3-6, SD3-5 and 2-19, isolated previously from paddy field soils, were classified into Methylosinus (W3-6) and Methylocystis (SD3-5 and 2-19) type II methanotrophs. Isolates from the rice roots (MD5-1, R62 and M1) grew logarithmically when casamino acid was used as the nitrogen source; however, the growth of these strains was reduced on the nitrate medium. These strains preferred amino acids over inorganic nitrogen as a nitrogen source for growth.

Hydathode morphology and role of guttation in excreting sodium at different concentrations of sodium chloride in eddo

Abstract Mature leaves of field-grown eddo plants were used for observing hydathode morphology by light and scanning electron microscopies. There were approximately five hydathode pores on the adaxial surface of each leaf tip. A ring structure with two borders around the pore was detected in this study. Further observations revealed a large cavity underneath the pores. The cavity was directly connected to vascular bundles that lacked a bundle sheath, via intercellular spaces among loosely organized parenchyma cells. Many crystal cells were present around the cavity and vascular bundles. To evaluate the role of guttation in sodium excretion under salinity stress, eddo plants were grown in hydroponic solutions containing 0, 1, 4, 8, and 12 mM sodium chloride (NaCl) for 7 d. As the NaCl concentration in the hydroponic solution increased, the sodium contents increased in leaf blades, petioles, and roots but remained unchanged in corms. The sodium concentration in the guttation fluid increased; however, the volume of guttation fluid decreased with increasing NaCl concentrations. Therefore, sodium elimination via guttation decreased with increasing NaCl concentrations. The ratios of the sodium content in guttation fluid to that of leaf blades, leaves, and whole plants decreased with increasing NaCl concentrations. The ratios of potassium to sodium contents in leaves, roots, and guttation fluid also decreased as the NaCl concentration increased. These results indicate that guttation did not eliminate sufficient sodium to play a role in adjusting sodium homeostasis and the ratios of potassium to sodium contents in eddo plants under saline conditions.