FA-SIFT study of the reactions of H₃O⁺∙(H₂O)n (n=0, 1, 2), NO⁺ and O₂˙⁺ with the terpenoid aldehydes citral, citronellal and myrtenal and their alcohol analogues

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Dynamische interactie tussen fotosynthese en BVOS emissies in bosecosystemen

Emissies van biogene vluchtige organische stoffen (BVOS), zoals isopreen, monoterpenen en sesquiterpenen, vormen een belangrijke bron van luchtvervuiling en dragen bij tot ozonvorming. Uit voorgaande studies blijkt dat deze emissies positief beïnvloed worden door licht en temperatuur. In het kader van dit onderzoek wordt nagegaan of ook fotosynthese een belangrijke interactie vertoont met BVOS-emissies. Continue en simultane metingen werden verricht met PTR-MS (metingen van BVOS-emissies) en IRGA (metingen van fotosynthese), beiden verbonden met cuvettes geïnstalleerd op verschillende hoogtes op takken van een volwassen beuk (Fagus sylvatica L.) in het experimentele proefbos Aelmoeseneie, Gontrode van augustus tot oktober 2008. Ook werden microklimatologische parameters opgemeten voor cuvettes

Study of biogenic volatile organic compound emissions and depositions over a mixed temperate forest by PTR-TOF-MS and eddy covariance

Volatile organic compounds (VOCs) play a key role in atmospheric chemistry. These gases impact air quality by participating in the formation of ozone and secondary organic aerosols and extend the lifetime of methane in the atmosphere. Approximately 90% of global VOC emissions are biogenic (BVOCs), and since forests are the main emitters of BVOCs, these ecosystems deserve special attention in order to better characterize BVOCs exchanges with the atmosphere. Traditionally, flux measurements were mainly limited to a few dominant BVOC species, such as isoprene, terpenes and methanol, due to technical measurement limitations. Most of the measured species were found to be emitted by vegetation, but some studies detected significant net depositions of compounds such as methanol, driven by environmental factors favouring the formation of surface wetness. This observation supports the need for a more detailed and complete picture of BVOC bidirectional exchanges at forest sites as well as the mechanisms controlling these fluxes, which are essential to better characterize the in-canopy atmospheric chemistry. To address this gap, BVOC fluxes were measured in spring-summer 2022 using a PTR-TOF-MS instrument (PTR-TOF-4000, Ionicon Analytik GmbH) over a mixed temperate forest in the Belgian Ardenne (Vielsalm), which is part of the ICOS network. The use of a PTR-TOF-MS instrument, deployed at Vielsalm in the framework of ACTRIS, allows for the simultaneous detection of a very wide range of VOC-related ion masses with increased sensitivity (especially for ions at high m/z ratios) and higher mass resolving power compared to conventional PTR-Quad-MS instruments. O3 fluxes were also simultaneously acquired using fast and slow ozone analysers in order to complete the BVOC fluxes dataset and BVOC+O3 concentration profiles were frequently measured at seven levels along the flux tower from ground level up to 51 m. (Un)calibrated BVOC mixing ratios were first derived from results of the Ionicon Data Analyzer software (IDA, Ionicon Analytik GmbH) obtained on a near-daily basis, and these concentrations were then used in a computational tool based on InnFLUX (Atmospheric Physics and Chemistry Group, University of Innsbruck) to compute fluxes by eddy covariance. Along with these fluxes, uncertainties and limits of detection (LODs) were estimated, and quality control statistical tests were performed. During the whole measurement campaign, about 570 m/z peaks were detected by the IDA software. Based on this extensive dataset, our goals are to: (1) perform spectral analysis (which often turns out to be trickier for low signal-to-noise ratios), (2) determine the significant fluxes based on LODs, (3) analyse their response to meteorological variables, phenology and O3 concentrations/fluxes, (4) attempt compound attribution based on scientific literature and site-related information, and (5) establish the budget of BVOC emissions and depositions for the forest site. The obtained results will be compared to BVOC studies previously conducted at the Vielsalm ICOS forest site with a PTR-Quad-MS instrument and should improve our previous BVOC budget estimates at the site.BERTRAC13. Climate actio

Decrease in the photosynthetic performance of temperate grassland species does not lead to a decline in the gross primary production of the ecosystem

Plants, under stressful conditions, can proceed to photosynthetic adjustments in order to acclimatize and alleviate the detrimental impacts on the photosynthetic apparatus. However, it is currently unclear how adjustment of photosynthetic processes under environmental constraints by plants influences CO2 gas exchange at the ecosystem-scale. Over a two-year period, photosynthetic performance of a temperate grassland ecosystem was characterized by conducting frequent chlorophyll fluorescence (ChlF) measurements on three primary grassland species (Lolium perenne L., Taraxacum sp., and Trifolium repens L.). Ecosystem photosynthetic performance was estimated from measurements performed on the three dominant grassland species weighed based on their relative abundance. In addition, monitoring CO2 fluxes was performed by eddy covariance. The highest decrease in photosynthetic performance was detected in summer, when environmental constraints were combined. Dicot species (Taraxacum sp. and T. repens) presented the strongest capacity to up-regulate PSI and exhibited the highest electron transport efficiency under stressful environmental conditions compared with L. perenne. The decline in ecosystem photosynthetic performance did not lead to a reduction in gross primary productivity, likely because increased light energy was available under these conditions. The carbon amounts fixed at light saturation were not influenced by alterations in photosynthetic processes, suggesting photosynthesis was not impaired. Decreased photosynthetic performance was associated with high respiration flux, but both were influenced by temperature. Our study revealed variation in photosynthetic performance of a grassland ecosystem responded to environmental constraints, but alterations in photosynthetic processes appeared to exhibit a negligible influence on ecosystem CO2 fluxes