Search

Remote sensing has become a valuable tool in monitoring arctic environments. The aim of this paper is ground-based hyperspectral characterization of Low Arctic Alaskan tundra communities along four environmental gradients (regional climate, soil pH, toposequence, and soil moisture) that all vary in ground cover, biomass, and dominating plant communities. Field spectroscopy in connection with vegetation analysis was carried out in summer 2012, along the North American Arctic Transect (NAAT). Spectral metrics were extracted, including the averaged reflectance and absorption-related metrics such as absorption depths and area of continuum removal. The spectral metrics were investigated with respect to "greenness", biomass, vegetation height, and soil moisture regimes. The results show that the surface reflectances of all sites are similar in shape with a reduced near-infrared (NIR) reflectance that is specific for low-growing biomes. The main spectro-radiometric findings are: (i) Southern sites along the climate gradient have taller shrubs and greater overall vegetation biomass, which leads to higher reflectance in the NIR. (ii) Vegetation height and surface wetness are two antagonists that balance each other out with respect to the NIR reflectance along the toposequence and soil moisture gradients. (iii) Moist acidic tundra (MAT) sites have "greener" species, more leaf biomass, and green-colored moss species that lead to higher pigment absorption compared to moist non-acidic tundra (MNT) sites. (iv) MAT and MNT plant community separation via narrowband Normalized Difference Vegetation Index (NDVI) shows the potential of hyperspectral remote sensing applications in the tundra. [ABSTRACT FROM AUTHOR]

Two new polyynes, named oplopantriol A (5) and oplopantriol B (6), were isolated from the root bark of Oplopanax horridus (Smith) Miq, an ethnic medicinal plant of North America, along with four known polyynes: (3S,8S)-falcarindiol (1), oplopandiol (2), (11S,16S,9Z)-9,17-octadecadiene-12,14-diyne-1,11,16-triol, 1-acetate (3) and oplopandiol acetate (4). The structures of the new compounds were elucidated by detailed spectroscopic analyses, including 1D and 2D NMR techniques and chemical methods. The absolute configurations of the new compounds 5 and 6 were determined by comparing their optical rotation values with the hydrolysis products of the known compounds 3 and 4, respectively, derived from the same plant. On the basis of an analysis of their physical and chemical properties we show that the alkaline hydrolysis of 3 and 4 afforded the new compounds 5 and 6, respectively. [ABSTRACT FROM AUTHOR]