Soil biogenic emissions of nitric oxide from arid and semi-arid ecosystems

The biogenic production of NO in the soil accounts for between 10% and 40% of the global total. A large degree of the uncertainty in the estimation of the biogenic emissions stems from a shortage of measurements in arid regions, which comprise 40% of the earth���s land surface area. This study examined the emission of NO from three ecosystems in southern Africa which cover an aridity gradient from semi-arid savannas in South Africa to the hyper-arid Namib Desert in Namibia. A laboratory method was used to determine the release of NO as a function of the soil moisture and the soil temperature. Various methods were used to up-scale the net potential NO emissions determined in the laboratory to the vegetation patch, landscape or regional level. The importance of landscape, vegetation and climatic characteristics is emphasized. The first study occurred in a semi-arid savanna region in South Africa, where soils were sampled from 4 landscape positions in the Kruger National Park. The maximum NO emission occurred at soil moisture contents of 10%-20% water filled pore space (WFPS). The highest net potential NO emissions came from the low lying landscape positions, which have the largest nitrogen (N) stocks and the largest input of N. Net potential NO fluxes obtained in the laboratory were converted in field fluxes for the period 2003-2005, for the four landscape positions, using soil moisture and temperature data obtained in situ at the Kruger National Park Flux Tower Site. The NO emissions ranged from 1.5-8.5 kg ha-1 a-1. The field fluxes were up-scaled to a regional basis using geographic information system (GIS) based techniques, this indicated that the highest NO emissions occurred from the Midslope positions due to their large geographical extent in the research area. Total emissions ranged from 20x103 kg in 2004 to 34x103 kg in 2003 for the 56000 ha Skukuza land type. The second study occurred in an arid savanna ecosystem in the Kalahari, Botswana. In this study I collected soils from four differing vegetation patch types including: Pan, Annual Grassland, Perennial Grassland and Bush Encroached patches. The maximum net potential NO fluxes ranged from 0.27 ng m-2 s-1 in the Pan patches to 2.95 ng m-2 s-1 in the Perennial Grassland patches. The net potential NO emissions were up-scaled for the year December 2005-November 2006. This was done using 1) the net potential NO emissions determined in the laboratory, 2) the vegetation patch distribution obtained from LANDSAT NDVI measurements 3) estimated soil moisture contents obtained from ENVISAT ASAR measurements and 4) soil surface temperature measurements using MODIS 8 day land surface temperature measurements. This up-scaling procedure gave NO fluxes which ranged from 1.8 g ha-1 month-1 in the winter months (June and July) to 323 g ha-1 month-1 in the summer months (January-March). Differences occurred between the vegetation patches where the highest NO fluxes occurred in the Perennial Grassland patches and the lowest in the Pan patches. Over the course of the year the mean up-scaled NO emission for the studied region was 0.54 kg ha-1 a-1 and accounts for a loss of approximately 7.4% of the estimated N input to the region. The third study occurred in the hyper-arid Namib Desert in Namibia. Soils were sampled from three ecosystems; Dunes, Gravel Plains and the Riparian zone of the Kuiseb River. The net potential NO flux measured in the laboratory was used to estimate the NO flux for the Namib Desert for 2006 using modelled soil moisture and temperature data from the European Centre for Medium Range Weather Forecasts (ECMWF) operational model on a 36km x 35km spatial resolution. The maximum net potential NO production occurred at low soil moisture contents (<10%WFPS) and the optimal temperature was 25��C in the Dune and Riparian ecosystems and 35��C in the Gravel Plain Ecosystems. The maximum net potential NO fluxes ranged from 3.0 ng m-2 s-1 in the Riparian ecosystem to 6.2 ng m-2 s-1 in the Gravel Plains ecosystem. Up-scaling the net potential NO flux gave NO fluxes of up to 0.062 kg ha-1 a-1 in the Dune ecosystem and 0.544 kg h-1 a-1 in the Gravel Plain ecosystem. From these studies it is shown that NO is emitted ubiquitously from terrestrial ecosystems, as such the NO emission potential from deserts and scrublands should be taken into account in the global NO models. The emission of NO is influenced by various factors such as landscape, vegetation and climate. This study looks at the potential emissions from certain arid and semi-arid environments in southern Africa and other parts of the world and discusses some of the important factors controlling the emission of NO from the soil.

Leaf level VOC emissions of single plants from Amazonian and Mediterranean ecosystems: Ontogeny and flooding as stress factor for VOC emissions

Die Vegetation ist die wichtigste Quelle von organischen fl��chtigen Verbindungen (auf Englisch volatile organic compounds,VOCs), die einen bemerkenswerten Einfluss auf der Chemie und Physik der Atmosph��re haben. VOCs beeinflussen die oxidative Kapazit��t der Atmosph��re und tragen zu der Bildung und zum Wachstum von sekund��ren organischen Aerosolen bei, welche einerseits eine Streuung und Reflektierung der Energie verursachen und andererseits sich an der Bildung und Entwicklung von Wolken beteiligen. Ziel dieser Arbeit war die Beschreibung und der Vergleich von VOC Emissionen aus Pflanzen aus zwei verschiedenen ��kosystemen: Mediterranes ��kosystem und Tropisches ��kosystem. F��r diese Aufgabe wurden gew��hnliche Pflanzen von beiden ��kosystemen untersucht. Siebzehn Pflanzenspezies aus der Mittelmeergebiet, welches bekannt ist f��r seine Vielfalt an VOC emittierenden Pflanzen, wurden in die Untersuchungen einbezogen. Im Gegensatz zum mediterranen ��kosystem sind nur wenig Information verf��gbar ��ber VOC Emissionen aus Bl��ttern tropischer Baumspezies. Vor diesem Hintergrund wurden sechsundzwanzig Baumspezies aus verschiedenen ��kotypen des Amazonasbeckens (Terra firme, V��rzea und Igap��) wurden auf VOC Emissionen auf Blattebene mit einem K��vetten-System untersucht. Analysen von fl��chtigen organischen Verbindungen wurden online mit PTR-MS und offline mittels Sammlung auf entsprechenden Adsorbern (Kartuschen) und nachfolgender GC-FID Analyse untersucht. Die h��chsten Emissionen wurden f��r Isoprene beobachtete, gefolgt durch Monoterpene, Methanol und Aceton. Die meisten Mittelmeer Spezies emittierten eine hohe Vielfalt an Monoterpenspezies, hingegen zeigten nur f��nf tropische Pflanzenspezies eine Monoterpene mit einen sehr konservativen Emissionsprofil (��-Pinen>Limonen>Sabinen >��-Pinen). Mittelmeerpflanzen zeigten zus��tzlich Emissionen von Sesquiterpenen, w��hrend bei der Pflanzen des Amazonas Beckens keine Sesquiterpenemissionen gefunden wurden. Dieser letzte Befund k��nnte aber auch durch eine niedrigere Sensitivit��t des Messsystems w��hrend der Arbeiten im Amazonasgebiet erkl��rt werden. Zus��tzlich zu den Isoprenoidemissionen waren Methanolemissionen als Indikator f��r Wachtumsvorg��nge sehr verbreitet in den meisten Pflanzenspezies aus tropischen und mediterranen Gebieten. Einige Pflanzenspezies beider ��kosystemen zeigten Acetonemissionen. rnrnVOC Emissionen werde durch eine gro��e Vielfalt an biotischen und abiotischen Faktoren wie Lichtintensit��t, Temperatur, CO2 und Trockenheit beeinflusst. Ein anderer, ��fter ��bersehener Faktor, der aber sehr wichtig ist f��r das Amazonas Becken, ist die regelm����ige ��berflutung. In dieser Untersuchung wir fanden heraus, dass am Anfang einer Wurzelanoxie, die durch die ��berflutung verursacht wurde, Ethanol und Acetaldehyd emittiert werden k��nnen, vor allem in Pflanzenspezies, die schlechter an eine unzureichende Sauerstoffversorgung bei Flutung adaptiert sind, wie z.B. Vatairea guianensis. Die Spezies Hevea spruceana, welche besser an ��berflutung adaptiert ist, k��nnte m��glicherweise der gebildete Ethanol sofort remetabolisieren ohne es zu emittieren. Nach einer langen Periode einer ��berflutung konnte allerdings keine Emission mehr beobachtet werden, was auf eine vollst��ndige Adaptation mit zunehmender Dauer schlie��en l��sst. Als Reaktion auf den ausgel��sten Stress k��nnen Isoprenoidemissionen ebenfalls kurzfristig nach einigen Tage an ��berflutung zunehmen, fallen dann aber dann nach einer langen Periode zusammen mit der Photosynthese, Transpiration und stomat��re Leitf��higkeit deutlich ab.rnrnPflanzen Ontogenese ist anscheinend von Bedeutung f��r die Qualit��t und Quantit��t von VOC Emissionen. Aus diesem Grund wurden junge und erwachsene Bl��tter einiger gut charakterisierten Pflanzen Spezies aus dem Mittelmeerraum auf VOC Emissionen untersucht. Standard Emissionsfaktoren von Isopren waren niedriger in jungen Bl��ttern als in erwachsene Bl��tter. Hingegen wurden h��here Monoterpen- und Sesquiterpenemissionen in jungen Bl��tter einiger Pflanzenspezies gefunden. Dieser Befund deutet auf eine potentielle Rolle dieser VOCs als Abwehrkomponenten gegen Pflanzenfresser oder Pathogene bei jungen Bl��tter hin. In einigen F��llen variierte auch die Zusammensetzung der Monoterpen- und Sesquiterpenspezies bei jungen und erwachsenen Bl��ttern. Methanolemissionen waren, wie erwartet, h��her in jungen Bl��ttern als in ausgewachsenen Bl��ttern, was mit der Demethylierung von Pectin bei der Zellwandreifung erkl��rt werden kann. Diese Befunde zu ��nderungen der Emissionskapazit��t der Vegetation k��nnen f��r zuk��nftige Modellierungen herangezogen werden. rn

Mediterranean-type climate in the South Aegean (Eastern Mediterranean) during the Late Miocene: Evidence from isotope and element proxies

The present-day climate in the Mediterranean region is characterized by mild, wet winters and hot, dry summers. There is contradictory evidence as to whether the present-day conditions (���Mediterranean climate���) already existed in the Late Miocene. This thesis presents seasonally-resolved isotope and element proxy data obtained from Late Miocene reef corals from Crete (Southern Aegean, Eastern Mediterranean) in order to illustrate climate conditions in the Mediterranean region during this time. There was a transition from greenhouse to icehouse conditions without a Greenland ice sheet during the Late Miocene. Since the Greenland ice sheet is predicted to melt fully within the next millennia, Late Miocene climate mechanisms can be considered as useful analogues in evaluating models of Northern Hemispheric climate conditions in the future. So far, high resolution chemical proxy data on Late Miocene environments are limited. In order to enlarge the proxy database for this time span, coral genus Tarbellastraea was evaluated as a new proxy archive, and proved reliable based on consistent oxygen isotope records of Tarbellastraea and the established paleoenvironmental archive of coral genus Porites. In combination with lithostratigraphic data, global 87Sr/86Sr seawater chronostratigraphy was used to constrain the numerical age of the coral sites, assuming the Mediterranean Sea to be equilibrated with global open ocean water. 87Sr/86Sr ratios of Tarbellastraea and Porites from eight stratigraphically different sampling sites were measured by thermal ionization mass spectrometry. The ratios range from 0.708900 to 0.708958 corresponding to ages of 10 to 7 Ma (Tortonian to Early Messinian). Spectral analyses of multi-decadal time-series yield interannual ��18O variability with periods of ~2 and ~5 years, similar to that of modern records, indicating that pressure field systems comparable to those controlling the seasonality of present-day Mediterranean climate existed, at least intermittently, already during the Late Miocene. In addition to sea surface temperature (SST), ��18O composition of coral aragonite is controlled by other parameters such as local seawater composition which as a result of precipitation and evaporation, influences sea surface salinity (SSS). The Sr/Ca ratio is considered to be independent of salinity, and was used, therefore, as an additional proxy to estimate seasonality in SST. Major and trace element concentrations in coral aragonite determined by laser ablation inductively coupled plasma mass spectrometry yield significant variations along a transect perpendicular to coral growth increments, and record varying environmental conditions. The comparison between the average SST seasonality of 7��C and 9��C, derived from average annual ��18O (1.1���) and Sr/Ca (0.579 mmol/mol) amplitudes, respectively, indicates that the ��18O-derived SST seasonality is biased by seawater composition, reducing the ��18O amplitude by 0.3���. This value is equivalent to a seasonal SSS variation of 1���, as observed under present-day Aegean Sea conditions. Concentration patterns of non-lattice bound major and trace elements, related to trapped particles within the coral skeleton, reflect seasonal input of suspended load into the reef environment. ��18O, Sr/Ca and non-lattice bound element proxy records, as well as geochemical compositions of the trapped particles, provide evidence for intense precipitation in the Eastern Mediterranean during winters. Winter rain caused freshwater discharge and transport of weathering products from the hinterland into the reef environment. There is a trend in coral ��18O data to more positive mean ��18O values (���2.7��� to ���1.7���) coupled with decreased seasonal ��18O amplitudes (1.1��� to 0.7���) from 10 to 7 Ma. This relationship is most easily explained in terms of more positive summer ��18O. Since coral diversity and annual growth rates indicate more or less constant average SST for the Mediterranean from the Tortonian to the Early Messinian, more positive mean and summer ��18O indicate increasing aridity during the Late Miocene, and more pronounced during summers. The analytical results implicate that winter rainfall and summer drought, the main characteristics of the present-day Mediterranean climate, were already present in the Mediterranean region during the Late Miocene. Some models have argued that the Mediterranean climate did not exist in this region prior to the Pliocene. However, the data presented here show that conditions comparable to those of the present-day existed either intermittently or permanently since at least about 10 Ma.

Global simulated soil biogenic nitric oxide (NO) emissions: Impact, improvement and innovation

rnNitric oxide (NO) is important for several chemical processes in the atmosphere. Together with nitrogen dioxide (NO2 ) it is better known as nitrogen oxide (NOx ). NOx is crucial for the production and destruction of ozone. In several reactions it catalyzes the oxidation of methane and volatile organic compounds (VOCs) and in this context it is involved in the cycling of the hydroxyl radical (OH). OH is a reactive radical, capable of oxidizing most organic species. Therefore, OH is also called the ���detergent��� of the atmosphere. Nitric oxide originates from several sources: fossil fuel combustion, biomass burning, lightning and soils. Fossil fuel combustion is the largest source. The others are, depending on the reviewed literature, generally comparable to each other. The individual sources show a different temporal and spatial pattern in their magnitude of emission. Fossil fuel combustion is important in densely populated places, where NO from other sources is less important. In contrast NO emissions from soils (hereafter SNOx) or biomass burning are the dominant source of NOx in remote regions.rnBy applying an atmospheric chemistry global climate model (AC-GCM) I demonstrate that SNOx is responsible for a significant part of NOx in the atmosphere. Furthermore, it increases the O3 and OH mixing ratio substantially, leading to a ���10% increase in the oxidizing efficiency of the atmosphere. Interestingly, through reduced O3 and OH mixing ratios in simulations without SNOx, the lifetime of NOx increases in regions with other dominating sources of NOx