Miguel Portillo-Estrada

Interaction between isoprene and ozone fluxes in a poplar plantation and its impact on air quality at the European level

The emission of isoprene and other biogenic volatile organic compounds from vegetation plays an important role in tropospheric ozone (O3) formation. The potentially large expansion of isoprene emitting species (e.g., poplars) for bioenergy production might, therefore, impact tropospheric O3 formation. Using the eddy covariance technique we have simultaneously measured fluxes isoprene, O3 and of CO2 from a poplar (Populus) plantation grown for bioenergy production. We used the chemistry transport model LOTOS-EUROS to scale-up the isoprene emissions associated with the existing poplar plantations in Europe, and we assessed the impact of isoprene fluxes on ground level O3 concentrations. Our findings suggest that isoprene emissions from existing poplar-for-bioenergy plantations do not significantly affect the ground level of O3 concentration. Indeed the overall land in Europe covered with poplar plantations has not significantly changed over the last two decades despite policy incentives to produce bioenergy crops. The current surface area of isoprene emitting poplars-for-bioenergy remains too limited to significantly enhance O3 concentrations and thus to be considered a potential threat for air quality and human health.

Contribution of volatile organic compound fluxes to the ecosystem carbon budget of a poplar short-rotation plantation

Biogenic volatile organic compounds (BVOCs) are major precursors of both ozone and secondary organic aerosols (SOA) in the troposphere and represent a non‐negligible portion of the carbon fixed by primary producers, but long‐term ecosystem‐scale measurements of their exchanges with the atmosphere are lacking. In this study, the fluxes of 46 ions corresponding to 36 BVOCs were continuously monitored along with the exchanges of mass (carbon dioxide and water vapor) and energy (sensible and latent heat) for an entire year in a poplar (Populus) short‐rotation crop (SRC), using the eddy covariance methodology. BVOC emissions mainly consisted of isoprene, acetic acid, and methanol. Total net BVOC emissions were 19.20 kg C ha−1 yr−1, which represented 0.63% of the net ecosystem exchange (NEE), resulting from −23.59 Mg C ha−1 yr−1 fixed as CO2 and 20.55 Mg C ha−1 yr−1 respired as CO2 from the ecosystem. Isoprene emissions represented 0.293% of NEE, being emitted at a ratio of 1 : 1709 mol isoprene per mol of CO2 fixed. Based on annual ecosystem‐scale measurements, this study quantified for the first time that BVOC carbon emissions were lower than previously estimated in other studies (0.5–2% of NEE) on poplar trees. Furthermore, the seasonal and diurnal emission patterns of isoprene, methanol, and other BVOCs provided a better interpretation of the relationships with ecosystem CO2 and water vapor fluxes, with air temperature, vapor pressure deficit, and photosynthetic photon flux density.

Emissions of carotenoid cleavage products upon heat shock and mechanical wounding from a foliose lichen

Carotenoids constitute a major target of chloroplastic photooxidative reactions, leading to the formation of several oxidized derivatives and cleavage products, some of which are volatile (VCCPs). Among them, β-cyclocitral (β-CC), at least, is a retrograde signaling molecule that modulates the activity of many key physiological processes. In the present work, we aimed to study whether β-CC and other VCCPs are released into the atmosphere from photosynthetic tissues. To overcome stomatal limitations, the foliose chlorolichen Lobaria pulmonaria was used as the model system, and the emissions of biogenic volatiles, induced by heat and wounding stresses, were monitored by proton-transfer reaction time-of-flight mass-spectrometry (PTR-TOF-MS) and gas-chromatography (GC-MS). Prior to stress treatments, VCCPs were emitted constitutively, accounting for 1.3 % of the total volatile release, with β-CC being the most abundant VCCP. Heat and wounding stresses induced a burst of volatile release, including VCCPs, and a loss of carotenoids. Under heat stress, the production of β-CC correlated positively with temperature. However the enhancement of production of VCCPs was the lowest among all the groups of volatiles analyzed. Given that the rates of carotenoid loss were three orders of magnitude higher than the release rates of VCCPs and that these compounds only represent a minor fraction in the blend of volatiles, it seems unlikely that VCCPs might represent a global stress signal capable of diffusing through the atmosphere to different neighboring individuals.

Assessing Ecosystem Isoprene Emissions by Hyperspectral Remote Sensing

This study examined the relationship between foliar isoprene emissions, light use efficiency and photochemical reflectance index (PRI) throughout the canopy profile and explored the contribution of xanthophyll cycle pigments versus other carotenoid pigments to the isoprene/PRI relationship. Foliar isoprene emissions within the canopy profile were measured in a high-density poplar plantation in Flanders (Belgium) during the 2016 growing season. The results confirmed that PRI was a promising estimator of isoprene emissions at canopy level. Interestingly, xanthophyll cycle pigments contributed more to isoprene biosynthesis than chlorophyll and drove the isoprene/PRI relationship. The simple independent pigment index and novel defined indices, such as the hyperspectral isoprene index and simple hyperspectral isoprene index, showed promising results and could be suitable estimators of isoprene emissions due to their strong relationship with the xanthophyll pool.

Genotypic variation in transpiration of coppiced poplar during the third rotation of a short-rotation bio-energy culture

The productivity of short‐rotation coppice (SRC) plantations with poplar (Populus spp.) strongly depends on soil water availability, which limits the future development of its cultivation, and makes the study of the transpirational water loss particularly timely under the ongoing climate change (more frequent drought and floods). This study assesses the transpiration at different scales (leaf, tree and stand) of four poplar genotypes belonging to different species and from a different genetic background grown under an SRC regime. Measurements were performed for an entire growing season during the third year of the third rotation in a commercial scale multigenotype SRC plantation in Flanders (Belgium). Measurements at leaf level were performed on specific days with a contrasted evaporative demand, temperature and incoming shortwave radiation and included stomatal conductance, stem and leaf water potential. Leaf transpiration and leaf hydraulic conductance were obtained from these measurements. To determine the transpiration at the tree level, single‐stem sap flow using the stem heat balance (SHB) method and daily stem diameter variations were measured during the entire growing season. Sap flow‐based canopy transpiration (Ec), seasonal dry biomass yield, and water use efficiency (WUE; g aboveground dry matter/kg water transpired) of the four poplar genotypes were also calculated. The genotypes had contrasting physiological responses to environmental drivers and to soil conditions. Sap flow was tightly linked to the phenological stage of the trees and to the environmental variables (photosynthetically active radiation and vapor pressure deficit). The total Ec for the 2016 growing season was of 334, 350, 483 and 618 mm for the four poplar genotypes, Bakan, Koster, Oudenberg and Grimminge, respectively. The differences in physiological traits and in transpiration of the four genotypes resulted in different responses of WUE.