Simultaneous leaf-level measurement of trace gas emissions and photosynthesis with a portable photosynthesis system

Abstract

Abstract. Plants emit considerable quantities of volatile organic compounds (VOCs), the identity and amount of which vary with temperature, light, and other environmental factors. Portable photosynthesis systems are a useful method for simultaneously quantifying in situ leaf-level emissions of VOCs and plant physiology. We present a comprehensive characterization of the LI-6800 portable photosynthesis system's ability to be coupled to trace gas detectors and measure leaf-level trace gas emissions, including limits in flow rates, environmental parameters, and VOC backgrounds. Instrument contaminants from the LI-6800 can be substantial but are dominantly complex molecules such as siloxanes that are structurally dissimilar to biogenic VOCs and thus unlikely to interfere with most leaf-level emissions measurements. We validate the method by comparing CO2 assimilation calculated internally by the portable photosynthesis system to measurements taken with an external CO2 gas analyzer; these assimilation measurements agree within 1 %. We also demonstrate both online and offline measurements of plant trace gas exchange using the LI-6800. Offline measurements by pre-concentration on adsorbent cartridges enable the detection of a broad suite of VOCs, including monoterpenes (e.g., limonene) and aldehydes (e.g., decanal). Online measurements can be more challenging if flow rates require dilution with ultrapure zero air. We use high-resolution time-of-flight chemical ionization mass spectrometry coupled to the LI-6800 to measure the direct plant emission of formic acid.

Measuring Biosphere–Atmosphere Exchange of Short-Lived Climate Forcers and Their Precursors

“…To measure leaflevel VOC emissions, we couple a portable photosynthesis system to trace-gas measurement systems. 29 This technique enables us to control environmental conditions (e.g., temperature, humidity, CO 2 ) over a known leaf area and to measure a variety of VOCs using different measurements systems, such as organic acids (via online mass spectrometry techniques) and monoterpenes (via thermal desorption of sorbent tubes coupled to off-line analysis). Branch enclosures are larger 38 Estimated atmospheric lifetimes for OH (2.0 × 10 6 molecules cm −3 , 12 h avg) and O 3 (7 × 10 11 molecules cm −3 , 24 h avg) are from Atkinson and Arey.…”

“…Here, we provide an example of variability in limonene emissions of ponderosa lemon (Citrus limon x Citrus medica) plants using a leaf chamber (LI-6800 Portable Photosynthesis System, LI-COR) coupled to sorbent tubes for offline analysis using thermal desorption gas chromatography mass spectrometry 29 (Figure 4). We compared the intraplant variability with 15 leaves on a single plant (1P × 15L) to the interplant variability with three leaves on each of five plants (5P × 3L).…”

The First Seasonal Snowfall Impacts Plant Photosynthesis and Monoterpene Emissions

“…Riches et al. (2020) provides further details on the thermal desorption and subsequent gas chromatography mass spectrometry of the samples. We calibrated monoterpenes with analytical standards.…”

“…ACTI-VOC and Sensidyne Gilian LFS-113DC) onto sorbent tubes and use the difference to quantify emissions. We describe the interface between the PPS and sorbent tubes elsewhere (Riches et al, 2020). The portable photosynthesis system was equipped with a 6 cm 2 leaf chamber and external light source (LI-COR, Inc. Multiphase Flash™ Fluorometer).…”

“…We analyzed the sorbent tubes using a thermal desorption unit (Markes Intl., Unity-xr), coupled with a gas chromatograph (Thermo Scientific TRACE 1310) with mass spectrometry detection (Thermo Scientific TSQ 8000 Eco Triple Quadrupole GC-MS/MS). Riches et al (2020) provides further details on the thermal desorption and subsequent gas chromatography mass spectrometry of the samples. We calibrated monoterpenes with analytical standards.…”