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Aims: To examine the effects of soil and climatic conditions on community structure of the sweet potato bacterial endophytes. Study Design: Sweet potato plants were cultivated in different soils and locations combinations Original Research Article

A species-specific latitudinal distribution of soybean rhizobia has been reported; Bradyrhizobium japonicum and B. elkanii dominate in nodules in northern and southern areas, respectively. The aim of this study was to elucidate whether temperature-dependent proliferation in soil or infection is more reliable for determining the latitudinal characteristic distribution of soybean-nodulating rhizobia under local climate conditions. Three study locations, Fukagawa (temperate continental climate), Matsue and Miyazaki (humid sub-tropical climate), were selected in Japan. Each soil sample was transported to the other study locations, and soybean cv. Orihime (non-Rj) was pot-cultivated using three soils at three study locations for two successive years. Species composition of Bradyrhizobium in the nodules was analyzed based on the partial 16S rRNA and 16S–23S rRNA ITS gene sequences. Two Bradyrhizobium japonicum (Bj11 and BjS10J) clusters and one B. elkanii (BeL7) cluster were phylogenetically sub-grouped into two (Bj11-1-2) and four clusters (BjS10J-1-4) based on the ITS sequence. In the Fukagawa soil, Bj11-1 dominated (80–87%) in all study locations. In the Matsue soil, the composition was similar in the Matsue and Miyazaki locations, in which BeL7 dominated (70–73%), while in the Fukagawa location, BeL7 decreased to 53% and Bj11-1 and BjS10J-3 increased. In the Miyazaki soil, BeL7 dominated at 77%, and BeL7 decreased to 13% and 33% in the Fukagawa and Matsue locations, respectively, while BjS10J-2 and BjS10J-4 increased. It was supposed that the B. japonicum strain preferably proliferated in the Fukagawa location, leading to its nodule dominancy, while in the Miyazaki location, temperature-dependent infection would lead to the nodule dominancy of B. elkanii, and both factors would be involved in the Matsue location.

Various cladding materials consisting of plain carbon steels with lower carbon concentrations and alloy steels with higher car bon concentrations have been considered to analyze the behavior of interdiffusion across the interface theoretically. The combina tion of the plain carbon steel and the alloy steel for the cladding was selected to make the chemical potential of carbon greater in the plain carbon steel than in the alloy steel. For the selection, the phase diagrams were computed with Thermo_ Calc. The theo retical analysis was carried out using DICTRA that is the software developed at the Royal Institute of Technology in Sweden. The analysis indicates that the up_ hill diffusion of carbon spontaneously occurs from the plain carbon steel to the alloy steel dur ing annealing at elevated temperatures. For example, the cladding material composed of a plain carbon steel with a concentration of 0.046 mass÷C and a 18Cr_ 8Ni stainless steel with a concentration of 0.06 mass÷C exhibits such an up_ hill diffusion at 1200 K, resulting in precipitation of Cr 23 C 6 at the cladding interface.