Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in ...the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation (S = 0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172 nm at S = 0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit = 0.14 ± 0.03), higher values for the accumulation mode (κAcc = 0.22 ± 0.05), and an overall mean value of κmean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.
For the past decade, observations of carbonyl sulfide (OCS or COS) have been investigated as a proxy for carbon uptake by plants. OCS is destroyed by enzymes that interact with CO2 during ...photosynthesis, namely carbonic anhydrase (CA) and RuBisCO, where CA is the more important one. The majority of sources of OCS to the atmosphere are geographically separated from this large plant sink, whereas the sources and sinks of CO2 are co-located in ecosystems. The drawdown of OCS can therefore be related to the uptake of CO2 without the added complication of co-located emissions comparable in magnitude. Here we review the state of our understanding of the global OCS cycle and its applications to ecosystem carbon cycle science. OCS uptake is correlated well to plant carbon uptake, especially at the regional scale. OCS can be used in conjunction with other independent measures of ecosystem function, like solar-induced fluorescence and carbon and water isotope studies. More work needs to be done to generate global coverage for OCS observations and to link this powerful atmospheric tracer to systems where fundamental questions concerning the carbon and water cycle remain.
This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems ...through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments. The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction. Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink. It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.
Although several per cent of net carbon assimilation can be re-released as isoprene emissions to the atmosphere by many tropical plants, much uncertainty remains regarding its biological ...significance. In a previous study, we detected emissions of isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) from tropical plants under high temperature/light stress, suggesting that isoprene is oxidized not only in the atmosphere but also within plants. However, a comprehensive analysis of the suite of isoprene oxidation products in plants has not been performed and production relationships with environmental stress have not been described. In this study, putative isoprene oxidation products from mango (Mangifera indica) branches under abiotic stress were first identified. High temperature/light and freeze–thaw treatments verified direct emissions of the isoprene oxidation products MVK and MACR together with the first observations of 3-methyl furan (3-MF) and 2-methyl-3-buten-2-ol (MBO) as putative novel isoprene oxidation products. Mechanical wounding also stimulated emissions of MVK and MACR. Photosynthesis under 13 CO 2 resulted in rapid (<30 min) labelling of up to five carbon atoms of isoprene, with a similar labelling pattern observed in the putative oxidation products. These observations highlight the need to investigate further the mechanisms of isoprene oxidation within plants under stress and its biological and atmospheric significance.
The Amazon rainforest in Brazil and the megacity of Beijing in China are two of the most strongly contrasting habitats on Earth. In both locations, volatile chemicals are emitted into the atmosphere ...affecting the local atmospheric chemistry, air quality and ecosystem health. In this study, the total reactivity in air available for reaction with the atmosphere's primary oxidant the OH radical, has been measured directly in both locations along with individual volatile organic compounds(VOC), nitrogen oxides(NOx), ozone(O3) and carbon dioxide(CO2). Peak daily OH-reactivity in the Amazon 72 s−1, (min. 27 s−1) was approximately three times higher than Beijing 26 s−1 (min. 15 s−1). However, diel ozone variation in Amazonia was small (∼5 ppb) whereas in Beijing ∼70 ppb harmful photochemical ozone was produced by early afternoon. Amazon OH-reactivity peaked by day, was strongly impacted by isoprene, and anticorrelated to CO2, whereas in Beijing OH-reactivity was higher at night rising to a rush hour peak, was dominated by NO2 and correlated with CO2. These converse diel cycles between urban and natural ecosystems demonstrate how biosphere control of the atmospheric environment is subverted by anthropogenic emissions.
•Atmospheric OH reactivity was measured in a rainforest and a megacity.•Amazon reactivity peaked by day, was isoprene dominated, and anticorrelated to CO2.•Beijing reactivity peak in rush hour, was dominated by NO2 and correlated with CO2.•With high daytime reactivity in the rainforest, ozone remains low and constant.•Despite lower reactivity in megacity air, ozone increased strongly by day.
Size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted over a full seasonal cycle at the remote Amazon Tall Tower ...Observatory (ATTO, March 2014--February 2015). In a preceding companion paper, we presented annually and seasonally averaged data and parametrizations (Part 1; Pöhlker et al., 2016a). In the present study (Part 2), we analyze key features and implications of aerosol and CCN properties for the following characteristic atmospheric conditions: Long-range-transport (LRT) events, which frequently bring Saharan dust, African biomass smoke, and sea spray aerosols into the Amazon Basin, mostly during February to April. The LRT episodes are characterized by a dominant accumulation mode (D.sub.Ait â 80 nm, N.sub.Ait â 120 cm.sup.-3 vs. D.sub.acc â 180 nm, N.sub.acc â 310 cm.sup.-3 ), an increased abundance of dust and salt, and relatively high hygroscopicity (κ.sub.Ait â 0.18, κ.sub.acc â 0.35). The coarse mode is also significantly enhanced during these events.
Plants emit a wide range of volatile organic compounds in response to damage by herbivores, and many of the compounds have been shown to attract the natural enemies of insect herbivores or serve for ...inter- and intra-plant communication. Most studies have focused on volatile emission in the laboratory while little is known about emission patterns in the field. We studied the emission of volatiles by
Trifolium pratense
(red clover) under both laboratory and field conditions. The emission of 24 compounds was quantified in the laboratory, of which eight showed increased emission rates after herbivory by
Spodoptera littoralis
caterpillars, including (
E
)-β-ocimene, the most abundant compound,
(Z)
-β-ocimene, linalool, (
E
)-β-caryophyllene, (
E,E
)-α-farnesene, 4,8-dimethyl-1,3,7-nonatriene (DMNT), 1-octen-3-ol, and methyl salicylate (MeSA). While most of these compounds have been reported as herbivore-induced volatiles from a wide range of plant taxa, 1-octen-3-ol seems to be a characteristic volatile of legumes. In the field,
T. pratense
plants with varying herbivore damage growing in established grassland communities emitted only 13 detectable compounds, and the correlation between herbivore damage and volatile release was more variable than in the laboratory. For example, the emission of (
E
)-β-ocimene, (
Z)
-β-ocimene, and DMNT actually declined with damage, while decanal exhibited increased emission with increasing herbivory. Elevated light and temperature increased the emission of many compounds, but the differences in light and temperature conditions between the laboratory and the field could not account for the differences in emission profiles. Our results indicate that the release of volatiles from
T. pratense
plants in the field is likely to be influenced by additional biotic and abiotic factors not measured in this study. The elucidation of these factors may be important in understanding the physiological and ecological functions of volatiles in plants.
Bioaerosols are considered to play a relevant role in atmospheric processes, but their sources, properties, and spatiotemporal distribution in the atmosphere are not yet well characterized. In the ...Amazon Basin, primary biological aerosol particles (PBAPs) account for a large fraction of coarse particulate matter, and fungal spores are among the most abundant PBAPs in this area as well as in other vegetated continental regions. Furthermore, PBAPs could also be important ice nuclei in Amazonia. Measurement data on the release of fungal spores under natural conditions, however, are sparse. Here we present an experimental approach to analyze and quantify the spore release from fungi and other spore-producing organisms under natural and laboratory conditions. For measurements under natural conditions, the samples were kept in their natural environment and a setup was developed to estimate the spore release numbers and sizes as well as the microclimatic factors temperature and air humidity in parallel to the mesoclimatic parameters net radiation, rain, and fog occurrence. For experiments in the laboratory, we developed a cuvette to assess the particle size and number of newly released fungal spores under controlled conditions, simultaneously measuring temperature and relative humidity inside the cuvette. Both approaches were combined with bioaerosol sampling techniques to characterize the released particles using microscopic methods. For fruiting bodies of the basidiomycetous species, Rigidoporus microporus, the model species for which these techniques were tested, the highest frequency of spore release occurred in the range from 62 % to 96 % relative humidity. The results obtained for this model species reveal characteristic spore release patterns linked to environmental or experimental conditions, indicating that the moisture status of the sample may be a regulating factor, whereas temperature and light seem to play a minor role for this species. The presented approach enables systematic studies aimed at the quantification and validation of spore emission rates and inventories, which can be applied to a regional mapping of cryptogamic organisms under given environmental conditions.
The emission of gaseous sulfur (S) compounds by plants is related to several factors, such as the plant S status or fungal infection. Hydrogen sulfide (H2S) is either released or taken up by the ...plant depending on the ambient air concentration and the plant demand for S. On the contrary, carbonyl sulfide (COS) is normally taken up by plants. In a greenhouse experiment, the dependence of H2S and COS exchange with ambient air on the S status of oilseed rape (Brassica napus L.) and on fungal infection with Sclerotinia sclerotiorum was investigated. Thiol contents were determined to understand their influence on the exchange of gaseous S compounds. The experiment revealed that H2S emissions were closely related to pathogen infections as well as to S nutrition. S fertilization caused a change from H2S consumption by S-deficient oilseed rape plants to a H2S release of 41 pg g–1 (dw) min–1 after the addition of 250 mg of S per pot. Fungal infection caused an even stronger increase of H2S emissions with a maximum of 1842 pg g–1 (dw) min–1 2 days after infection. Healthy oilseed rape plants acted as a sink for COS. Fungal infection caused a shift from COS uptake to COS releases. The release of S-containing gases thus seems to be part of the response to fungal infection. The roles the S-containing gases may play in this response are discussed.
Biological particles suspended in the atmosphere have a crucial role in the dynamics of the biosphere underneath. Although much attention is paid for the chemical and physical properties of these ...particles, their biological taxonomic identity, which is relevant for ecological research, remains little studied. We took air samples at 300 meters above the forest in central Amazonia, in seven periods of 7 days, and used high-throughput DNA sequencing techniques to taxonomically identify airborne fungal and plant material. The use of a molecular identification technique improved taxonomic resolution when compared to morphological identification. This first appraisal of airborne diversity showed that fungal composition was strikingly different from what has been recorded in anthropogenic regions. For instance, basidiospores reached 30% of the OTUs instead of 3–5% as found in the literature; and the orders Capnodiales and Eurotiales—to which many allergenic fungi and crop pathogens belong—were much less frequently recorded than Pleosporales, Polyporales, and Agaricales. Plant OTUs corresponded mainly to Amazonian taxa frequently present in pollen records such as the genera
Helicostilys
and
Cecropia
and/or very abundant in the region such as
Pourouma
and
Pouteria
. The origin of extra-Amazonian plant material is unknown, but they belong to genera of predominantly wind-pollinated angiosperm families such as Poaceae and Betulaceae. Finally, the detection of two bryophyte genera feeds the debate about the role of long distance dispersal in the distribution of these plants.
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