Spatial Variabillity of Soil Nitrogen Dynamics slong a Slope in a Cryptomeria japonica D.Don Plantation

Spatial variabillity of soil nitrogen(N) dynamics was examined along a slope in a 45-year-old Cryptomeria japonica D.Don plantation in the southeastern paet of Shiga Prefecture. Net N mineralization showed no clear gradient along the slope, while net nitrification and percent nitrification were high at lower positions,and very low at upper positions of the slope. Principal component(PC) analysis showed soil properties were divided into three groups which were PC1(water content and pH), and PC3(total C and N). Regressions of net soil N transformations against PCs scores suggested net N mincralization was mainly regulated by PC3, while net nitrification and percent nitrification were mainly regulated by PC1 and PC2. The difference in the main form of inorganic N was expected to affect soil N availability for plants through the difference in the mobility in negatively changed forest soil. We evaluated the soil N availability that reflebted the ion mobility factors by ion exchange resins and found that greater mobility of nitrate lead to greater soil N availability at lower positions of the slope. In addition, gross N transformations were directly measured using 15N isotope dilution, and the influence of microbial caebon (C) availability on the internal soil N cycles were examined by long-term laboratory incubation. Gross nitrifivation was detected in both soils taken at upper and lower positions on the slope, suggesting that nitrification was also an important process at upper positions where almost no net nitrification was detected. Changes in net and gross N transformations, the organic C and N pools, and microbial respiration suggested that start of rapid net nitrifibation might be affected not only by the availability of C for microbial biomass, but also by the relative availability of C and N

Nitrate-use traits of understory plants as potential regulators of vegetation distribution on a slope in a Japanese cedar plantation

[Background and Aims] Plant physiological traits and their relation to soil N availability was investigated as regulators of the distribution of understory shrub species along a slope in a Japanese cedar (Cryptomeria japonica) plantation in central Japan. [Methods]At the study site, previous studies demonstrated that both net and gross soil nitrification rates are high on the lower slope and there are dramatic declines in different sections of the slope gradient. We examined the distributions of understory plant species and their nitrate (NO3[-]-N) use traits, and compared the results with the soil traits. [Results]Our results show that boundaries between different dominant understory species correspond to boundaries between different soil types. Leucosceptrum stellipilum occurs on soil with high net and gross nitrification rates. Hydrangea hirta is dominant on soil with high net and low gross nitrification rates. Pieris japonica occurs on soil with very low net and gross nitrification rates. Dominant understory species have species-specific physiological traits in their use of NO3[-]-N. Pieris japonica lacks the capacity to use NO3[-]-N as a N source, but other species do use NO3[-]-N. Lindera triloba, whose distribution is unrelated to soil NO3[-]-N availability, changes the extent to which it uses NO3[-]-N in response to soil NO3[-]-N availability. [Conclusions]Our results indicate that differences in the physiological capabilities and adaptabilities of plant species in using NO3[-]-N as a N source regulate their distribution ranges. The identity of the major form of available soil N is therefore an environmental factor that influences plant distributions

Enhancement of the anomalous Hall effect and spin glass behavior in the bilayered manganite La(2-2x)Sr(1+2x)Mn2O7

The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La(2-2x)Sr(1+2x)Mn2O7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system.Comment: 7 pages, 4 figures, Solid State Communications (in press

Transient differential reflectivity of ferromagnetic and paramagnetic phases in the bilayered manganite La1.24Sr1.76Mn2O7

Photoinduced effects in a single crystal of bilayered manganites, La2-2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of hundred picoseconds was observed just below Tc=127K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of ten picoseconds. This fast relaxing component, whose absolute value has an asymmetric peak at Tc, is presumably due to short-range correlation of Jahn-Teller distortion.Comment: 13 pages, 4 figures, accepted to Solid State Communication

Agouti protein, mahogunin, and attractin in pheomelanogenesis and melanoblast-like alteration of melanocytes: a cAMP-independent pathway

Melanocortin-1 receptor (MC1R) and its ligands, a-melanocyte stimulating hormone (aMSH) and agouti signaling protein (ASIP), regulate switching between eumelanin and pheomelanin synthesis in melanocytes. Here we investigated biological effects and signaling pathways of ASIP. Melan-a non agouti (a ⁄ a) mouse melanocytes produce mainly eumelanin, but ASIP combined with phenylthiourea and extra cysteine could induce over 200-fold increases in the pheomelanin to eumelanin ratio, and a tan-yellow color in pelletted cells.Moreover, ASIP-treated cells showed reduced proliferation and a melanoblast-like appearance, seen also in melanocyte lines from yellow (Ay ⁄ a and Mc1re ⁄ Mc1re) mice. However ASIP-YY, a C-terminal fragment of ASIP, induced neither biological nor pigmentary changes. As, like ASIP, ASIP-YY inhibited the cAMP rise induced by aMSH analog NDP-MSH, and reduced cAMP level without added MSH, the morphological changes and depigmentation seemed independent of cAMP signaling. Melanocytes genetically null for ASIP mediators attractin or mahogunin (Atrnmg-3J ⁄ mg-3J or Mgrn1md-nc ⁄ md-nc) also responded to both ASIP and ASIP-YY in cAMP level, while only ASIP altered their proliferation and (in part) shape. Thus, ASIP–MC1R signaling includes a cAMP-independent pathway through attractin and mahogunin, while the known cAMP-dependent component requires neither attractin nor mahogunin.Parts of the research were supported by Wellcome Trust program grants 064583 and 078327 to D.C.B. and E.V.S.; the Japan Society for the Promotion of Science KAKENHI (grants 20790808 to T.H. and 18591262 and 20591357 to K.W. and S.I.); a Grant-in-Aid from the Japanese Ministry of Health, Labour and Welfare (K.J.), the Spanish Ministry of Education and Science BFU2006-12185 (L.M.), the South West Academic Network (A.J.D. and E.V.S.), and NIH grant DK064265 (B.Y. and G.L.M.).Peer reviewe

アモルファスおよびカイラル磁性体における秩序スピン状態の理論研究

Tohoku University藤田全基課