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Biogenic isoprene emissions from herbaceous plants are generally lower than those from trees. However, our study finds widespread isoprene emission in herbaceous sedge plants, with a stronger temperature response surpassing current tree-derived models. We measured and compared isoprene emissions from sedges grown in different climatic zones, all showing an exponential temperature response with a Q10 range of 7.2 to 12, significantly higher than the Q10 of about 3 for other common isoprene emitters. The distinct temperature sensitivity of sedges makes them a hidden isoprene source, significant during heat waves but not easily detected in mild weather. For instance, isoprene emissions fromCarex praegraciliscan increase by 320% with a peak emission of over 100 nmol m⁻²s⁻¹compared to preheat wave emissions. During heat waves, the peak isoprene emissions fromC. praegraciliscan match those fromLophostemon confertus, a commonly used street tree species which is considered the dominant urban isoprene source due to higher biomass and emission capacities. This surge in isoprene from globally distributed sedges, including those in urban landscapes, could contribute to peak ozone and aerosol pollutants during heat waves. 

Abstract In recent decades, there has been a significant increase in annual area burned in California’s Sierra Nevada mountains. This rise in fire activity has prompted the need to understand how historical forest management practices affect fuel composition and emissions. Here we examined the total carbon (TC) concentration and radiocarbon abundance (Δ 14 C) of particulate matter (PM) emitted by the KNP Complex Fire, which occurred during California’s 2021 wildfire season and affected several groves of giant sequoia trees in the southern Sierra Nevada. During a 26 h sampling period, we measured concentrations of fine airborne PM (PM 2.5 ), as well as dry air mole fractions of carbon monoxide (CO) and methane (CH 4 ), using a ground-based mobile laboratory. We also collected filter samples of PM 2.5 for analysis of TC concentration and Δ 14 C. High correlation among PM 2.5 , CO, and CH 4 time series confirmed that our PM 2.5 measurements captured variability in wildfire emissions. Using a Keeling plot approach, we determined that the mean Δ 14 C of PM 2.5 was 111.6 ± 7.7‰ ( n = 12), which was considerably enriched relative to atmospheric carbon dioxide in the northern hemisphere in 2021 (−3.2 ± 1.4‰). Combining these Δ 14 C data with a steady-state one-box ecosystem model, we estimated that the mean age of fuels combusted in the KNP Complex Fire was 40 years, with a range of 29–57 years. These results provide evidence for emissions originating from woody biomass, larger-diameter fine fuels, and coarse woody debris that have accumulated over multiple decades. This is consistent with independent field observations that indicate high fire intensity contributed to widespread giant sequoia mortality. With the expanded use of prescribed fires planned over the next decade in California to mitigate wildfire impacts, our measurement approach has the potential to provide regionally-integrated estimates of the effectiveness of fuel treatment programs. 

Key Points With COVID‐19 restrictions, carbon dioxide (CO 2 ) levels on Los Angeles (LA) freeways were reduced by 119 ppm (or 60%) in July 2020 relative to 2019 Plant radiocarbon analysis captured a 5 ppm reduction in LA' fossil fuel CO 2 levels during the Stay‐At‐Home order Mobile and plant‐based measurements of fossil fuel CO 2 can help quantify decarbonization progress in cities 

Abstract Non‐growing season CO₂emissions from Arctic tundra remain a major uncertainty in forecasting climate change consequences of permafrost thaw. We present the first time series of soil and microbial CO₂emissions from a graminoid tundra based on year‐round in situ measurements of the radiocarbon content of soil CO₂(Δ¹⁴CO₂) and of bulk soil C (Δ¹⁴C), microbial activity, and temperature. Combining these data with land‐atmosphere CO₂exchange allows estimates of the proportion and mean age of microbial CO₂emissions year‐round. We observe a seasonal shift in emission sources from fresh carbon during the growing season (August Δ¹⁴CO₂ = 74 ± 4.7‰, 37% ± 3.4% microbial, mean ± se) to increasingly older soil carbon in fall and winter (March Δ¹⁴CO₂ = 22 ± 1.3‰, 47% ± 8% microbial). Thus, rising soil temperatures and emissions during fall and winter are depleting aged soil carbon pools in the active layer and thawing permafrost and further accelerating climate change.