We investigate soil based on both plant production and nutrient cycling standpoint.
Soil provides nutrients to plants, which supports sustainable food production. We investigate this soil function, and are challenging to reveal the unknown area of soil function in natural ecosystems as well as in agricultural land. For example, some plants are growing in severe conditions. Rhizobium and arbuscular mycorrhizal fungi are suspected of helping plants grow under those conditions. We study the interaction between the plants and microbes, and the nutrient cycle using biochemical and molecular biological techniques.
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Most tree roots are infected by mycorrhizal fungi that give nutrients in the soil to those trees and also take up photosynthetic products from the host-trees. These fungi establish symbiotic relationships with their host-plants. We have investigated whether the nutrient requirements of the host plant play a role of infection to the plants by mycorrhizal fungi.
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In Japan, about 80% of soybeans are cultivated in upland fields converted from paddy fields. The growth of soybeans in the fields is generally not well, and the yields are low. Both rice and soy establish symbiotic relationships with arbuscular mycorrhizal (AM) fungi. Recently, it has been suggested that AM fungi show some host-specificity. We investigate the diversity of AM fungi in soybean in upland fields under paddy-upland rotation, and the effects of diversity on the growth of the host-soybeans.
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After cultivation, the water in paddy fields is drained until next planting. These days, some paddy fields are re-flooded after the cultivation, and water is kept there during the winter season. By doing so, the paddy fields provide habitat for aquatic organisms and preserve biodiversity. However, the flooded paddy fields develop the reductive condition and eliminate methane, one of the greenhouse gasses, from the subsurface soil in the winter season. Furthermore, the cycles of nutrients, such as phosphorus, nitrogen, sulfur, and iron, should be different from those of conventional cropping systems. We investigate the effects of cropping systems on the material cycles in paddy fields and rice growth.
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Soil is a complex system involving inorganic and organic compounds and organisms. Investigating the cycles of those compounds, including carbon, nitrogen, sulfur, oxygen, and so on, are essential to understand environmental and agricultural systems. For example, root nodules of leguminous plants are symbiotic organs to Rhizobium bacteria. The bacteria fix nitrogen in the atmosphere. Therefore, the nitrogen in leguminous plants comes from soil and atmosphere. Nitrogen stable isotope ratio (15N/14N) is the most efficient tool for exploring the origin of nitrogen in the leguminous plants. We investigate material (nitrogen, carbon, sulfur, and oxygen) cycle in soil by using stable isotopes.
The supplies of nutrients from the soil to plants are due to the nutrient retention capacity of the soil. In other words, the soil can retain contaminants. We research the sorption of inorganic and organic chemicals on soils, and the uptake of those chemicals in soil by plants.
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Soil particles sorb both inorganic and organic pollutants. Understanding the mechanism of the sorption of these pollutants into the soil is essential for studying bioavailability and toxicity. We investigate the behavior of contaminants in soil with the hope of contributing to both human and ecosystem health.