Tadakatsu Yoneyama

Atmospheric dinitrogen fixation in the flooded rice rhizosphere as determined by the N-15 isotope technique

Abstract Atmospheric nitrogen fixation in the rice rhizosphere was determined under in situ conditions of growing flooded rice using the N-15 isotope method. The whole plant growing in a pot at a reproductive stage was placed in a specially designed glass container and exposed to a 15N2 atmosphere. The amounts of total nitrogen fixed in the rice rhizosphere under the experimental conditions were 1366, 592, 878, and 698 μg per pot containing 0.4 kg of soil during 15N2 exposure for 7 to 13 days in the four experiments conducted in this study. It was also found that the nitrogen fixed in the rice rhizosphere was translocated into other plant parts. Nineteen to 25% of the total atmospheric nitrogen fixed in the rice rhizosphere was found in the roots, leaves and stems, and ears of the rice plants during the 15N2 exposure period.

Absorption of atmospheric NO2 by plants and soils

Abstract Tomato, sunflower and com plants were grown in culture solution containing three different concentrations of 15N-Iabelled KNO3 (260 ppm N, 105 ppm N, and 26 ppm N) as a nitrogen nutrient, and fumigated with 0.3 ppm NO2 for 2 weeks during their vegetative stages. The amount of NO2 nitrogen absorbed into the plants was estimated by “difference method” and “15N method.” “15N method” was found to give more probable values than “difference method.” According to “15N method,” the nitrogen derived from NO3 was about 16% (tomato), 22% (sunflower), and 14% (com) of the increased amount of total nitrogen in the whole plants in the 105 ppm N plot, and these percentages increased in the 26 ppm N plot. Difference in nitrogen concentration of the culture solution resulted in big change in the dryweight increase of the tomato and sunflower plants, but the absorption rate of NO2 nitrogen based on the dry weight changed slightly. The absorption rate of NO2 nitrogen was around 0.8 mg (gDW)-1 day-1 in tomato and su...

DECOMPOSITION OF RICE RESIDUES IN TROPICAL SOILS : IV. The Effect of Rice Straw on Nitrogen Fixation by Heterotrophic Bacteria in Some Philippine Soils

The acetylene-reducing activity of waterlogged soils was stimulated by the incorporation of rice straw at a relatively early stage of its decomposition. The straw caused a decrease in the inorganic nitrogen and in redox potential, making a favorable environment for N2-fixing bacteria. But the stimulation of nitrogen fixation was observed only when the soils were kept waterlogged. Soils of Maahas and Banaue which had not been air dried showed a fairly high acetylene-reducing activity when rice straw was incorporated at a ratio of 0.5 or 1.0 percent. Also the rice stubble showed high acetylene-reducing activity when the stubbled soil was kept waterlogged.

Nitrogen mineralization of sewage sludges in soil

Abstract The returning of sewage sludges or animal manure into crop fields is considered to be one of the most effective methods in reducing the use of industrially produced fertilizer, which consumes high cost oil energy, as well as utilizing the mineral nutrients in the wastes for crop production. If this route of mineral cycling is developed, careful examination is needed to protect crop lands and human environment from any possible pollution problem. Sometimes sewage contains a high amount of heavy metals (2) and usually contains a large amount of nitrogenous compounds, which are mostly microbial proteins and easily mineralized into ammonia or nitrate. The heavy metals and inorganic nitrogen (mainly nitrate) may cause a pollution problem to our environment, if their concentration in the soil is high. High nitrate content of vegetables is sometimes a result of a high concentration of nitrate in soil (7). The run-off of inorganic nitrogen from agricultural lands is considered to be one of the causes of ...

Transfer of nitrogen and carbon from a mature sunflower leaf - 15NO2 and 13CO2 feeding studies.

To investigate the long-distance transport of nitrogen and carbon from mature leaves, two stable isotopes, (15)N and (13)C, were introduced to a single mature sunflower leaf for less than 2 hr in the forms of NO2 and CO2, and the fate of (15)N and (13)C in plants was followed. In the first experiment, about 4 ppm (15)NO2 was applied to a mature sunflower leaf for 65 min in light, and the fate of (15)N was followed over 72 hr. (15)NO2 absorbed in sunflower was first incorporated into the ethanol-soluble fraction, then gradually incorporated into the ethanol-insoluble fraction: after 24 hr, only 12% remained in the soluble fraction in the fed leaf. Some (15)N was transferred from the fed leaf, first to the stems and next to the young growing leaves and roots, although negligible transfer to other mature leaves was detected. In the second experiment, 3.1 ppm (15)NO2 and 300-400 ppm (13)CO2 were simultaneously introduced to a single mature leaf for 110 min in light, and the fate of the two isotopes was followed for 28 days. Most of the (13)C transfer from the fed leaf took place within 1 day, whereas the transfer of (15)N continued gradually during the experimental period after a small rapid transfer within 1 day. Just after isotope feeding, the ratios of transferred (13)C to (15)N were high in all parts and remained high in the lower stem and the root, although they decreased very rapidly in the upper leaves and the upper stem. In the root, (15)N did not show a significant loss while some (13)C loss occurred during the experimental period. The transfer of (13)C and (15)N to the lower leaves was very low. (13)C Studies showed that carbon of the flower originated from both reserved carbon and current photosynthates.

Microbial degradation of 15N-labeled rice residues in soil during two years' incubation under flooded and upland conditions

Abstract Rice residues labeled with 15N were incorporated in soil and incubated under flooded and upland conditions, and the distribution and transformation of the residual nitrogen in various soil fractions were traced over 2 years. Immobilization of a large amount of soil nitrogen by plant residues brought about a decrease in net mineralized soil-nitrogen, though some residue-origin nitrogen was mineralized. Under flooded conditions large amount of nitrogen loss occurred, probably through denitrification. On the contrary, the loss was very small under upland conditions. Incorporation of soil nitrogen into the rice residues occurred mostly, within the first month, and thereafter the percentages of residue-origin nitrogen in the total plant debris nitrogen did not change so much in the four large size fractions, though decay continued to the end of incubation (24 months). Decrease of residue-origin nitrogen in the plant debris fractions partly resulted in nitrogen tranfer to the silt with fine sand fracti...

Absorption of atmospheric nitrogen dioxide by rice, wheat, and barley plants: estimation by the 15N-dilution method

Understanding of the impact of air pollutants on ecological systems has recently advanced in many aspects. Air pollutant absorption by plants is one of the important aspects involving the plants in ecological systems. We devised a 15N method for the quantitative estimation of the amount of nitrogen dioxide (NO2) absorbed by plants over a long period (2, 5). First, in a water culture experiment, 15N was administered as medium nitrogen from which the atmospheric NO2-nitrogen absorbed in the plants was discriminated (2). This 15N method was then modified in a soil culture experiment where 15N was applied as a fertilizer nitrogen and the amount of NO2-nitrogen in the plants was estimated by introducing the assumption that the ratios of fertilizer nitrogen to soil nitrogen absorbed in control and NO2-fumigated plants are the same in each of various plant parts investigated (5). In a previous report (5), it was found that the equation proposed by Fried and Middelboe (1) for the measurement of the amount of dini...

DETECTION OF N-NITROSODIMETHYLAMINE IN SOILS AMENDED WITH SLUDGES

Intensive cultivation of crop fields using agricultural chemicals and fertilizers has led to changes in ecological systems, resulting in a high possibility of environmental pollution by contamination, or occasional reactions not only in the soil but also in the water and the atmosphere. Some substances are known to be very toxic to human beings at low concentrations. For example, nitrosamines are believed to be carcinogenic and mutagenic.

Nitrite utilization in the roots of higher plants

Abstract Nitrite utilization by the roots of kidney bean, corn, and sunflower plants was investigated using 15N-labeled nitrite, and the following were concluded. (1) The primary roots of the corn plant assimilate nitrite to amino acids by a combination of nitrite reductase, glutamine synthetase and glutamate synthase. The reduction rate is rapid in the apical zone compared to the rates in the more mature zones. (2) Nitrite reduction to amino level occurs rapidly in the roots of 20-day-old seedlings of the three plants at similar rates in the daytime and in the night. This reduction seems to be more rapid than the reduction of nitrate to amino level. (3) The nitrogen derived from fed nitrogen was transferred from the root to the leaf more actively in the daytime than in the night. This trend was true for both the nitrite-fed and nitrate-fed plants. However, nitrite does not seem to be transferred to the leaf, but some nitrate may be transferred in an unchanged form.