Search

Numerous biogenic volatile organic compounds (VOC) species are released into the atmosphere from tropical forests. Measuring all those which are relevant for atmospheric chemistry or for the carbon budget is challenging. Large-Scale Biosphere-Atmosphere (LBA) Experiment field campaigns substantially increased the number of field studies of isoprene and monoterpene emissions, as well as of the exchange of several other VOC species. This chapter reports about the progress made within LBA from primary emission measurements at the plant species level up to discussions of the oxidative capacity of the atmosphere and formation of secondary organic aerosol particles and cloud condensation nuclei from biogenic hydrocarbons. VOC emission from Amazonian ecotypes has strong effects on atmospheric chemistry, which are obviously not fully understood in the case of the tropical atmosphere. Atmospheric flux studies within numerous field experiments resulted in new knowledge about local to regional scale biogenic VOC exchange and improved modeling. New data obtained from field as well as from laboratory studies helped to characterize VOC emissions from the Amazonian forest underlying seasonality within dry and wet seasons. Furthermore, first insight was obtained into the potential of floodplain areas affected by long-lasting flooding periods which can cause special emission adaptation. © Copyright 2009 by the American Geophysical Union.

We estimate isoprene emissions over tropical South America during 1997-2001 using column measurements of formaldehyde (HCHO) from the Global Ozone Monitoring Experiment (GOME) satellite instrument, the GEOS-Chem chemistry transport model, and the MEGAN (Model of Emissions of Gases and Aerosols from Nature) bottom-up isoprene inventory. GEOS-Chem is qualitatively consistent with in situ ground-based and aircraft concentration profiles of isoprene and HCHO, and GOME HCHO column data (r = 0.41; bias = +35%), but has less skill in reproducing wet season observations. Observed variability of GOME HCHO columns over South America is determined largely by isoprene and biomass burning. We find that the column contributions from other biogenic volatile organic compounds (VOC) are typically smaller than the column fitting uncertainty. HCHO columns influenced by biomass burning are removed using Along Track Scanning Radiometer (ATSR) firecounts and GOME NO2 columns. We find that South America can be split into eastern and western regions, with fires concentrated over the eastern region. A monthly mean linear transfer function, determined by GEOS-Chem, is used to infer isoprene emissions from observed HCHO columns. The seasonal variation of GOME isoprene emissions over the western region is broadly consistent with MEGAN (r = 0.41; bias = -256%), with largest isoprene emissions during the dry season when the observed variability is consistent with knowledge of temperature dependence. During the wet season other unknown factors play a significant role in determining observed variability. Copyright 2008 by the American Geophysical Union.

5‐Oxo‐prolinase of cultured tobacco cells is a soluble enzyme predominantly localized in the cytoplasm. To get optimal enzyme activity, the presence of the monovalent cation ammonium and the divalent cations Mg2+ and Mn2+ in the assay mixture is necessary. The enzyme has an extremely alkaline pH—(9.5–10.5) and a high temperature ‐ optimum (55°C). In contrary to the 5‐oxo‐prolinase from animal cells, where heat‐stabilization by 5‐oxo‐proline is observed, the high temperature optimum of the tobacco enzyme is due to stabilization by ATP. High 5‐oxo‐prolinase activity in tobacco cell homogenates was not only shown with the co‐substrate ATP, but with other purine‐nucleotides, too, although ATP was the best co‐substrate of the compounds tested. Substrate affinity of the tobacco enzyme (Km 5‐oxo‐proline = 30.5 μM) is similar to that demonstrated for wheat germ 5‐oxo‐prolinase. Competitive inhibition by the 5‐oxo‐proline analogues 2‐imidazolidone‐4‐carboxylic acid(K1= 14.5 μM) and dihydroorotic acid (K1=2 mM) revealed a much higher sensitivity of tobacco 5‐oxo‐prolinase to these compounds than observed for the mammalian enzyme. [ABSTRACT FROM AUTHOR]