Plant species vary in the amounts of P they obtain from the soil. It was hypothesized that investigation of the differences among species with a mathematical model describing the processes involved in P uptake from soil, would both show why species varied and provide a more rigorous test of a model verified for corn (Zea mays L.). A controlled climate chamber experiment was conducted with six plant species varying in ability to grow in soils at low levels of soil P. The soil and plant parameters required to operate the model were measured and the agreement between predicted P uptake and observed P uptake evaluated. When the roots were considered to be smooth cylinders absorbing P from soil solution, several species absorbed more P than predicted by the model. The species varied widely in root hair length and density. When the contribution of root hairs to P uptake was included, predicted P uptake agreed with observed uptake. A linear regression gave an r of 0.89 and a slope of 0.89. In addition to root hairs, P uptake efficiency of the plant species was influenced by amount of root surface per gram of plant, rate of plant growth, and the P influx kinetics of the root.
Huge amounts of radionuclides, particularly radiocesium, were discharged from the Fukushima Daiichi Nuclear Power Plant (FDNPP), and widespread of contamination of the land, including paddy fields, was observed. Because rice is a staple food in Japan, contamination of paddy fields is a serious problem, and practical countermeasures to reduce radiocesium contamination of rice are urgently required. Potassium (K) fertilization was previously shown to be an effective countermeasure in fields contaminated by the Chernobyl accident, but researchers did not study the effects on rice (Oryza sativa L.). In the present study, we performed urgent field experiments to test the use of K fertilization, as well as other soil amendments, to reduce radiocesium contamination of rice. We found that K fertilization was an effective and practical countermeasure to reduce radiocesium uptake by rice from several soil types in Japanese paddy rice culture. Other treatments, including the application of expanded vermiculite or manure, were effective, and the effect appears to be explained by their K content. Based on these results, the recommended level of exchangeable soil potassium to lower the radiocesium content of rice to acceptable levels is about 200 mg K kg -1 soil before the usual fertilization. This K fertilizer application criterion was applied in a wide, low-contaminated area from the 2012 cropping season, and satisfactory results have been obtained generally.
Root hairs increase phosphorus, P, uptake over that due to the plant root alone. A mechanistic model using 16 parameters was developed to describe this process. The model was verified with an experiment using six species that varied widely in root hair length, density and radius. A sensitivity analysis was conducted and the results are included to illustrate the situations where root hairs contribute significantly to P uptake. Length of root hair, root hair density and root hair radius all influenced predicted P uptake with root hair length being particularily significant.
Environmental samples of soil, plant and air dust collected after the Fukushima Daiichi Nuclear Power Plant accident were analyzed by autoradiograph, and significant amounts of radioactive particles containing higher cesium-134 ( 134 Cs) and cesium-137 ( 137 Cs) were found. Most of the radioactive soil particles were clay sized. The main part of the radioactivity and radioactive particles of air dust was detected from the 1.1-2.0μm fraction of an Andersen sampler filter. A considerable part of the radioactive particles on the air dust filter were not water soluble. Radioactive particles attached to outdoor plant leaves persisted for nearly 1 year. Thus, soil, leaf and air dust similarly contained sparingly water-soluble, micron-sized radioactive particles each with comparable ranges of elevated radio-Cs. A sheet dilution method was proposed and used to select and purify these radioactive particles. Using selected radioactive particles, the relation between area × gray value on autoradiograph and radioactivity was estimated. Radioactivity per particle was up to a few Bq and the geometrical average radioactivity of detected particles was around 0.1 Bq per particle or less. The configuration, chemical composition, origin and formation mechanisms of the radioactive particles require clarification.
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