We estimated the isoprene and monoterpene source strengths of a pristine tropical forest north of Manaus in the central Amazon Basin using three different micrometeorological flux measurement ...approaches. During the early dry season campaign of the Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001), a tower-based surface layer gradient (SLG) technique was applied simultaneously with a relaxed eddy accumulation (REA) system. Airborne measurements of vertical profiles within and above the convective boundary layer (CBL) were used to estimate fluxes on a landscape scale by application of the mixed layer gradient (MLG) technique. The mean daytime fluxes of organic carbon measured by REA were 2.1 mg C m−2 h−1 for isoprene, 0.20 mg C m−2 h−1 for α-pinene, and 0.39 mg C m−2 h−1 for the sum of monoterpenes. These values are in reasonable agreement with fluxes determined with the SLG approach, which exhibited a higher scatter, as expected for the complex terrain investigated. The observed VOC fluxes are in good agreement with simulations using a single-column chemistry and climate model (SCM). In contrast, the model-derived mixing ratios of VOCs were by far higher than observed, indicating that chemical processes may not be adequately represented in the model. The observed vertical gradients of isoprene and its primary degradation products methyl vinyl ketone (MVK) and methacrolein (MACR) suggest that the oxidation capacity in the tropical CBL is much higher than previously assumed. A simple chemical kinetics model was used to infer OH radical concentrations from the vertical gradients of (MVK+MACR)/isoprene. The estimated range of OH concentrations during the daytime was 3–8×106 molecules cm−3, i.e., an order of magnitude higher than is estimated for the tropical CBL by current state-of-the-art atmospheric chemistry and transport models. The remarkably high OH concentrations were also supported by results of a simple budget analysis, based on the flux-to-lifetime relationship of isoprene within the CBL. Furthermore, VOC fluxes determined with the airborne MLG approach were only in reasonable agreement with those of the tower-based REA and SLG approaches after correction for chemical decay by OH radicals, applying a best estimate OH concentration of 5.5×106 molecules cm−3. The SCM model calculations support relatively high OH concentration estimates after specifically being constrained by the mixing ratios of chemical constituents observed during the campaign. The relevance of the VOC fluxes for the local carbon budget of the tropical rainforest site during the measurements campaign was assessed by comparison with the concurrent CO2 fluxes, estimated by three different methods (eddy correlation, Lagrangian dispersion, and mass budget approach). Depending on the CO2 flux estimate, 1–6% or more of the carbon gained by net ecosystem productivity appeared to be re-emitted through VOC emissions.
Whereas for extra‐tropical regions model estimates of the emission of volatile organic compounds (VOC) predict strong responses to the strong annual cycles of foliar biomass, light intensity and ...temperature, the tropical regions stand out as a dominant source year round, with only little variability mainly due to the annual cycle of foliar biomass of drought‐deciduous trees. As part of the Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA‐EUSTACH), a remote secondary tropical forest site was visited in the dry‐to‐wet season transition campaign, and the trace gas exchange of a strong isoprene emitter and a monoterpene emitter are compared to the wet‐to‐dry season transition investigations reported earlier. Strong seasonal differences of the emission capacity were observed. The standard emission factor for isoprene emission of young mature leaves of Hymenaea courbaril was about twofold in the end of the dry season (111.5 μgC g−1 h−1 or 41.2 nmol m−2 s−1) compared to old mature leaves investigated in the end of the wet season (45.4 μgC g−1 h−1 or 24.9 nmol m−2 s−1). Standardized monoterpene emission rate of Apeiba tibourbou were 2.1 and 3.6 μgC g−1 h−1 (or 0.3 and 0.8 nmol m−2 s‐1), respectively. This change in species‐specific VOC emission capacity was mirrored by a concurrent change in the ambient mixing ratios. The growth conditions vary less in tropical areas than in temperate regions of the world, and the seasonal differences in emission strength could not be reconciled solely with meteorological data of instantaneous light intensity and temperature. Hence the inadequacy of using a single standard emission factor to represent an entire seasonal cycle is apparent. Among a host of other potential factors, including the leaf developmental stage, water and nutrient status, and abiotic stresses like the oxidative capacity of the ambient air, predominantly the long‐term growth temperature may be applied to predict the seasonal variability of the isoprene emission capacity. The dry season isoprene emission rates of H. courbaril measured at the canopy top were also compared to isoprene emissions of the shade‐adapted species Sorocea guilleminiana growing in the understory. Despite the difference in VOC emission composition and canopy position, one common algorithm was able to predict the diel emission pattern of all three tree species.
As part of the project LBA‐EUSTACH (European Studies on Trace gases and Atmosphere Chemistry as a contribution to the Large‐Scale Biosphere‐Atmosphere experiment in Amazonia), we examined the diel ...pattern of isoprenoid exchange in the wet season of 1999 at a remote field site in Rondônia, Brazil. The emission pattern of two tree species in a secondary forest was investigated by means of a dynamic branch enclosure system and was compared on the basis of climatological variables like temperature and light and physiological parameters such as assimilation, transpiration, and stomatal conductance. While the species Hymenaea courbaril was found to be a strong isoprene emitter, Apeiba tibourbou was found to exclusively emit monoterpenes and no isoprene. Species‐related standard emission factors calculated on a carbon basis were 45.4 μg g−1 h−1 (24.9 nmol m−2 s−1) for isoprene and 3.6 μg g−1 h−1 (0.75 nmol m−2 s−1) for monoterpene emission, representing a nontrivial carbon loss by the plants of 1.8% and 0.1% C relative to the net carbon assimilation on a daily basis. About 90% of the total monoterpene emission from A. tibourbou was comprised of sabinene, α‐pinene, β‐pinene, myrcene, and limonene, in decreasing quantity. Despite the difference in isoprenoid emission composition, the diel emission pattern of both tree species reacted similarly toward the environmental conditions, fluctuating light and temperature, indicating that closely related metabolic controls were involved in the actual emission. Both isoprene emission and monoterpene emission exhibited a light saturation curve similar to CO2 assimilation. No isoprenoid emission was found during nighttime. The strong light dependence of the monoterpene emission by A. tibourbou suggests that this tree species does not store monoterpenes but emits them immediately upon production. The diel pattern of both the isoprene and the monoterpene emission could be adequately simulated by current isoprene algorithms. The ambient air mixing ratios of isoprenoids were clearly dominated by isoprene, with peak values of 8 ppb inside the main canopy. Vertical gradients of ambient air mixing ratios in and above a primary rain forest site illustrated the emission of isoprene by the main canopy dependent upon light and temperature but were also indicative of a potential sink at the forest floor. For monoterpenes, corresponding gradients could hardly be resolved, reflecting observed ambient air mixing ratios more than an order of magnitude lower than for isoprene. Nevertheless, a strong diel cycle of short‐lived monoterpene compounds like α‐pinene was found in the primary as well as in the secondary forest site, which further strengthens our finding of a strong light dependence of biogenic monoterpene emission even on a larger scale. Our findings to some extent question the applicability of the commonly used monoterpene emission algorithm to the tropics. A strong light dependence of biogenic monoterpene emissions may, if generalized for tropical tree species in common, have a strong impact on estimated global flux rates for tropical regions.
According to recent assessments, tropical woodlands contribute about half of all global natural non-methane volatile organic compound (VOC) emissions. Large uncertainties exist especially about ...fluxes of compounds other than isoprene and monoterpenes. During the Large-Scale Biosphere/Atmosphere Experiment in Amazonia – Cooperative LBA Airborne Regional Experiment 1998 (LBA-CLAIRE-98) campaign, we measured the atmospheric mixing ratios of different species of VOC at a ground station at Balbina, Amazonia. The station was located 100
km north of Manaus, SE of the Balbina reservoir, with 200–1000
km of pristine forest in the prevailing wind directions. Sampling methods included DNPH-coated cartridges for carbonyls and cartridges filled with graphitic carbons of different surface characteristics for other VOCs. The most prominent VOC species present in air were formaldehyde and isoprene, each up to several ppb. Concentrations of methylvinyl ketone as well as methacroleine, both oxidation products of isoprene, were relatively low, indicating a very low oxidation capacity in the lower atmospheric boundary layer, which is in agreement with a daily ozone maximum of <20
ppb. Total monoterpene concentration was below 1
ppb. We detected only very low amounts of VOC species, such as benzene, deriving exclusively from anthropogenic sources.
We report on the emission of monoterpenes, short-chained organic acids and aldehydes from Mediterranean oak (
Quercus ilex L.) and pine (Pinus
pinea L.). All studies were done with dynamic cuvettes ...enclosing intact branches at the top of the canopy flushed with ambient air. Daily trends are compared with the photosynthetic active radiation (PAR), leaf temperature and the physiological activities of the enclosed branches, i.e. assimilation and transpiration, with special attention on the carbon budget. Oak emits monoterpenes in high amounts, up to 2% of the assimilated carbon. As compared with monoterpenes, short-chained organic acids and aldehydes are of minor importance for oak. However, on a leaf dry-weight basis equal amounts of acids and aldehydes are released from oak and pine. As pine emitted only low amounts of terpenes (below 0.2% of the assimilated carbon) the release of terpenes and oxygenated compounds is of equal importance for this species. A comparison of a modelled light and temperature driven emission with the observed volatile organic compounds (VOC) emissions showed good agreement for monoterpenes as well as for organic acids emitted in the case of oak. For pine only the release of acids showed an adequate relation to the algorithm data, whereas the terpene emissions seemed to be dominated by temperature effects.
Tolerance of wood decay fungi of the genera
Agrocybe, Armillaria, Auricularia, Daedalea, Pleurotus, Trametes to the presence of various amounts of creosote-treated wood (CTW) in the growth medium was ...compared. In the case of the most tolerant strain,
Pleurotus ostreatus SMR 684, extracellular laccase and peroxidase specific activities were monitored during growth in the presence of CTW. Degradation of various creosote-constituting polycyclic aromatic hydrocarbons by this strain was evaluated by GC–MS and the ecotoxicity of treated and untreated CTW was compared by Microtox test.
VOC emission from orange orchards was determined in the framework of two field campaigns aimed at assessing the contribution of vegetation emissions to tropospheric ozone formation in the Valencia ...Citrus belt. Branch emission from different varieties of Citrus sinensis and Citrus Clementi was dominated by β‐caryophyllene during the summer period and by linalool during the blossoming season (April‐May). Large emission of D‐limonene from soil was also measured. Data collected with the enclosure technique were upscaled to determine canopy emission rates of terpene compounds. Values obtained were compared with fluxes measured by relaxed eddy accumulation. Substantial removal of β‐caryophyllene and linalool was detected during transport from the canopy into the atmospheric boundary layer. While within‐canopy removal of the sesquiterpene component was fully consistent with laboratory studies indicating the high reactivity of this compound with ozone, linalool losses were more difficult to explain. Although high canopy fluxes of acetone and acetaldehyde suggested linalool decomposition by gas‐phase reactivity, removal by heterogeneous chemistry seems the more likely explanation for the observed losses.
The possibility afforded by a new relaxed eddy accumulation system in the determination of emission and deposition fluxes of volatile organic compounds (VOCs) by chromatographic techniques will be ...presented. The system, especially designed to limit sampling artifacts, uses adsorption traps filled with solid sorbents as reservoirs for VOC collection. Enriched compounds were analyzed by capillary GC and positive identification and quantification of eluted compounds was achieved by mass-spectrometric detection. The method has been used to quantify the emission and deposition of both biogenic and anthropogenic VOCs over a Mediterranean forest ecosystem located in Central Italy. For the first time, both daily and seasonal trends of anthropogenic and biogenic VOCs will be reported. The consistency of monoterpene fluxes with predictions based on the knowledge of VOC emission from the dominant vegetation species will be tested. Data have been used to develop a novel algorithm to predict the seasonality of biogenic emission from the forest ecosystem.
We report on some results of our studies of monoterpene and isoprene emissions and the physiological activities of an oak species (
Quercus ilex L.) under the Mediterranean climatic conditions found ...at Castel Porziano (Rome) in June 1993. The oak species
Quercus ilex L. was found to emit mainly monoterpenes in high amounts. Isoprene emissions were negligible. Diel cycles of monoterpene emissions showed correlation with light and the diel behaviour of photosynthetic CO
2 assimilation, transpiration and stomatal conductance. Temperature dependence seemed to be of minor importance.
Quercus ilex L. leaves emit terpenes but do not have specialized structures for terpene storage. We exploited this unique feature to investigate terpene biosynthesis in intact leaves of Q. ilex. ...Light induction allowed us to distinguish three classes of terpenes: (i) a rapidly induced class including alpha-pinene; (ii) a more slowly induced class, including cis-beta-ocimene; and (iii) the most slowly induced class, including 3-methyl-3-buten-1-ol. Using 13C, we found that alpha-pinene and cis-beta-ocimene were labeled quickly and almost completely while there was a delay before label appeared in linalool and 3-methyl-3-buten-1-ol. The acetyl group of 3-methyl-3-buten-1-yl acetate was labeled quickly but label was limited to 20% of the moiety. It is suggested that the ocimene class of monoterpenes is made from one or more terpenes of the alpha-pinene class and that both classes are made entirely from reduced carbon pools inside the chloroplasts. Linalool and 3-methyl-3-buten-1-ol are made from a different pool of reduced carbon, possibly in nonphotosynthetic plastids. The acetyl group of the 3-methyl-3-buten-1-yl acetate is derived mostly from carbon that does not participate in photosynthetic reactions. Low humidity and prolonged exposure to light favored ocimenes emission and induced linalool emission. This may indicate conversion between terpene classes.
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