Isoprene emission and photosynthesis during heat waves and drought in black locust

Extreme weather conditions, like heat waves and drought, can substantially affect tree physiology and the emissions of biogenic volatile organic compounds (BVOC), including isoprene. To date, however, there is only limited understanding of BVOC emission patterns during prolonged heat and coupled heat–drought stress as well as post-stress recovery. To assess the impacts of heat and heat–drought stress on BVOC emissions, we studied gas exchange and isoprene emissions of black locust trees under controlled environmental conditions. Leaf gas exchange of isoprene, CO2 and H2O was quantified using branch chambers connected to a protontransfer-reaction mass spectrometer and an infrared gas analyzer. Heat and heat–drought stress resulted in a sharp decline of photosynthesis and stomatal conductance. Simultaneously, isoprene emissions increased six- to eight-fold in the heat and heat–drought treatment and resulted in a carbon loss that was equivalent to 12 % and 20 % of assimilated carbon at the time of measurement. Once temperature stress was released at the end of two 15 days long heat waves, stomatal conductance remained reduced, while isoprene emissions and photosynthesis recovered quickly to values of the control trees. Further, we found isoprene emissions to co-vary with net photosynthesis during non-stressful conditions, while during the heat waves, isoprene emissions could be solely described by non-linear functions of light and temperature. However, when isoprene emissions betweentreatments were compared under the same temperature and light conditions (e.g., T = 30° C, PAR = 500 µmol m−2 s−1), heat and heat–drought stressed trees would emit less isoprene than control trees. Ourfindings suggest that different parameterizations of light and temperature functions are needed in order to predict tree isoprene emissions under heat and combined heat–drought stress

Isoprene emission and photosynthesis during heatwaves and drought in black locust

Extreme weather conditions like heatwaves and drought can substantially affect tree physiology and the emissions of isoprene. To date, however, there is only limited understanding of isoprene emission patterns during prolonged heat stress and next to no data on emission patterns during coupled heat–drought stress or during post-stress recovery. We studied gas exchange and isoprene emissions of black locust trees under episodic heat stress and in combination with drought. Heatwaves were simulated in a controlled greenhouse facility by exposing trees to outside temperatures +10 °C, and trees in the heat–drought treatment were supplied with half of the irrigation water given to heat and control trees. Leaf gas exchange of isoprene, CO2 and H2O was quantified using self-constructed, automatically operating chambers, which were permanently installed on leaves (n = 3 per treatment). Heat and combined heat–drought stress resulted in a sharp decline of net photosynthesis (Anet) and stomatal conductance. Simultaneously, isoprene emissions increased 6- to 8-fold in the heat and heat–drought treatment, which resulted in a carbon loss that was equivalent to 12 and 20 % of assimilated carbon at the time of measurement. Once temperature stress was released at the end of two 15-day-long heatwaves, stomatal conductance remained reduced, while isoprene emissions and Anet recovered quickly to values of the control trees. Further, we found that isoprene emissions covaried with Anet during nonstress conditions, while during the heatwaves, isoprene emissions were not related to Anet but to light and temperature. Under standard air temperature and light conditions (here 30 °C and photosynthetically active radiation of 500 µmol m−2 s−1), isoprene emissions of the heat trees were by 45 % and the heat–drought trees were by 27 % lower than in control trees. Moreover, temperature response curves showed that not only the isoprene emission factor changed during both heat and heat–drought stress, but also the shape of the response. Because introducing a simple treatment-specific correction factor could not reproduce stress-induced isoprene emissions, different parameterizations of light and temperature functions are needed to describe tree isoprene emissions under heat and combined heat–drought stress. In order to increase the accuracy of predictions of isoprene emissions in response to climate extremes, such individual stress parameterizations should be introduced to current BVOC models

Tracing plant source water dynamics during drought by continuous transpiration measurements : An in-situ stable isotope approach

Publisher Copyright: © 2022 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.The isotopic composition of xylem water (δX) is of considerable interest for plant source water studies. In-situ monitored isotopic composition of transpired water (δT) could provide a nondestructive proxy for δX-values. Using flow-through leaf chambers, we monitored 2-hourly δT-dynamics in two tropical plant species, one canopy-forming tree and one understory herbaceous species. In an enclosed rainforest (Biosphere 2), we observed δT-dynamics in response to an experimental severe drought, followed by a 2H deep-water pulse applied belowground before starting regular rain. We also sampled branches to obtain δX-values from cryogenic vacuum extraction (CVE). Daily flux-weighted δ18OT-values were a good proxy for δ18OX-values under well-watered and drought conditions that matched the rainforest's water source. Transpiration-derived δ18OX-values were mostly lower than CVE-derived values. Transpiration-derived δ2HX-values were relatively high compared to source water and consistently higher than CVE-derived values during drought. Tracing the 2H deep-water pulse in real-time showed distinct water uptake and transport responses: a fast and strong contribution of deep water to canopy tree transpiration contrasting with a slow and limited contribution to understory species transpiration. Thus, the in-situ transpiration method is a promising tool to capture rapid dynamics in plant water uptake and use by both woody and nonwoody species.Peer reviewe

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis pathways

In the near future, climate change will cause enhanced frequency and/or severity of droughts in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with implications for carbon cycling and atmospheric chemistry that are challenging to predict. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission. To address this gap, we used position-specific 13C-pyruvate labeling to investigate leaf CO2 and VOC fluxes from four tropical species before and during a controlled drought in the enclosed rainforest of Biosphere 2 (B2). Overall, plants that were more drought-sensitive had greater reductions in daytime CO2 production. Although daytime CO2 production was always dominated by non-mitochondrial processes, the relative contribution of CO2 from the tricarboxylic acid cycle tended to increase under drought. A notable exception was the legume tree Clitoria fairchildiana R.A. Howard, which had less anabolic CO2 production than the other species even under pre-drought conditions, perhaps due to more efficient refixation of CO2 and anaplerotic use for amino acid synthesis. The C. fairchildiana was also the only species to allocate detectable amounts of 13C label to VOCs and was a major source of VOCs in B2. In C. fairchildiana leaves, our data indicate that intermediates from the mevalonic acid (MVA) pathway are used to produce the volatile monoterpene trans-β-ocimene, but not isoprene. This apparent crosstalk between the MVA and methylerythritol phosphate pathways for monoterpene synthesis declined with drought. Finally, although trans-β-ocimene emissions increased under drought, it was increasingly sourced from stored intermediates and not de novo synthesis. Unique metabolic responses of legumes may play a disproportionate role in the overall changes in daytime CO2 and VOC fluxes in tropical forests experiencing drought

A study of the transport conditions for selected solar energetic electron events

The release of energetic particles by solar flares offers the possibility to study the interaction of charged particles with fluctuations in magnetised plasmas and to obtain information about the particle transport in astrophysical objects. Within this work the received data set of observations from the WIND 3D plasma experiment was carefully processed and analysed for four selected solar particle events. In the four cases the raw data were corrected for influences caused by the Sun before the resulting pitch angle distributions were computed using the magnetic field information also measured by the WIND spacecraft. Further a calculation of the experimental intensity and anisotropy profiles of the particles during the four different events was performed. The calculated high resolution pitch angle distribution and anisotropy curves were compared for different energies as well as for the four selected events. Afterwards the transport parameters for the selected events - e.g. the parallel mean free path - were received by a modelling of the theoretical curves, given by the solution of the equation of focussed transport, to the experimental curves in intensity and anisotropy by the same time.Validerat; 20101217 (root

Validation of farm-scale methane emissions using nocturnal boundary layer budgets

This study provides the first experimental validation of Swiss agricultural methane emission estimates at the farm scale. We measured CH4 concentrations at a Swiss farmstead during two intensive field campaigns in August 2011 and July 2012 to (1) quantify the source strength of livestock methane emissions using a tethered balloon system and (2) to validate inventory emission estimates via nocturnal boundary layer (NBL) budgets. Field measurements were performed at a distance of 150 m from the nearest farm buildings with a tethered balloon system in combination with gradient measurements at eight heights on a 10 m tower to better resolve the near-surface concentrations. Vertical profiles of air temperature, relative humidity, CH4 concentration, wind speed, and wind direction showed that the NBL was strongly influenced by local transport processes and by the valley wind system. Methane concentrations showed a pronounced time course, with highest concentrations in the second half of the night. NBL budget flux estimates were obtained via a time–space kriging approach. Main uncertainties of NBL budget flux estimates were associated with nonstationary atmospheric conditions and the estimate of the inversion height zi (top of volume integration). The mean NBL budget fluxes of 1.60 ± 0.31 μg CH4 m-2 s-1 (1.40 ± 0.50 and 1.66 ± 0.20 μg CH4 m-2 s-1 in 2011 and 2012 respectively) were in good agreement with local inventory estimates based on current livestock number and default emission factors, with 1.29 ± 0.47 and 1.74 ± 0.63 μg CH4 m-2 s-1 for 2011 and 2012 respectively. This indicates that emission factors used for the national inventory reports are adequate, and we conclude that the NBL budget approach is a useful tool to validate emission inventory estimates.ISSN:1680-7375ISSN:1680-736

Validation of farm-scale methane emissions using nocturnal boudary layer budgets

ISSN:1680-7375ISSN:1680-736

Gas exchange of Aleppo Pine seedlings including emissions of biogenic volatile organic compounds during repeated hetawaves, drought and recovery period

The data describes plant gas exchange dynamics (CO2, H2O) together with online proton transfer reaction mass spectrometry measurements of biogenic volatile organic compound emissions of Pinus halepensis seedlings exposed to two similar heatwaves together with drought and a recovery period. Measured in a scientific glasshouse facility at KIT IMK-IFU Garmisch-Partenkirchen, Germany, via an automated chamber setup

Gap-filling strategies for annual VOC flux data sets

Up to now the limited knowledge about the ex-change of volatile organic compounds (VOCs) between thebiosphere and the atmosphere is one of the factors whichhinders more accurate climate predictions. Complete long-term flux data sets of several VOCs to quantify the annualexchange and validate recent VOC models are basically notavailable. In combination with long-term VOC flux mea-surements the application of gap-filling routines is inevitablein order to replace missing data and make an importantstep towards a better understanding of the VOC ecosystem–atmosphere exchange on longer timescales.We performed VOC flux measurements above a mountainmeadow in Austria during two complete growing seasons(from snowmelt in spring to snow reestablishment in late au-tumn) and used this data set to test the performance of fourdifferent gap-filling routines, mean diurnal variation (MDV),mean gliding window (MGW), look-up tables (LUT) and lin-ear interpolation (LIP), in terms of their ability to replacemissing flux data in order to obtain reliable VOC sums. Ac-cording to our findings the MDV routine was outstandingwith regard to the minimization of the gap-filling error forboth years and all quantified VOCs. The other gap-fillingroutines, which performed gap-filling on 24 h average val-ues, introduced considerably larger uncertainties. The errorwhich was introduced by the application of the different fill-ing routines increased linearly with the number of data gaps.Although average VOC fluxes measured during the winterperiod (complete snow coverage) were close to zero, thesewere highly variable and the filling of the winter period re-sulted in considerably higher uncertainties compared to theapplication of gap-filling during the measurement period.The annual patterns of the overall cumulative fluxes forthe quantified VOCs showed a completely different behaviour in 2009, which was an exceptional year due tothe occurrence of a severe hailstorm, compared to 2011.Methanol was the compound which, at 381.5 mg C m−2and449.9 mg C m−2, contributed most to the cumulative VOCcarbon emissions in 2009 and 2011, respectively. In contrastto methanol emissions, however, considerable amounts ofmonoterpenes (−327.3 mg C m−2)were deposited onto themountain meadow during 2009 caused by a hailstorm. Otherquantified VOCs had considerably lower influences on the annual patterns.ISSN:1810-6277ISSN:1810-628

Source partitioning of atmospheric methane using stable carbon isotope measurements in the Reuss Valley, Switzerland

ISSN:1025-6016ISSN:1477-263