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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. 

Rapid warming is likely increasing primary production and wildfire occurrence in the Arctic. Projected changes in the abundance and composition of carbonaceous aerosols during the summer are likely to impact atmospheric chemistry and climate, but our understanding of these processes is limited by sparse observations. Here, we characterize carbonaceous aerosol at two field sites, Toolik Field Station in the Interior and the Atmospheric Radiation Measurement facility at Utqiaġvik on the Arctic coast of Alaska, USA, through the summers of 2022 and 2023. We estimated particulate matter ≤2.5 micrometers (PM2.5) and particulate matter ≤10 micrometers (PM10) using laser light scattering (PurpleAir sensors) and examined total carbon (TC) and its organic carbon (OC) and elemental carbon (EC) fractions in total suspended particles (TSP). We also investigated the dominant sources of carbonaceous aerosol using air mass backward-trajectories from the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and radiocarbon source apportionment of TC. We found TC concentrations were about twice as high in the Interior than on the coast and that modern sources were the dominant sources of carbonaceous aerosol at both Toolik (95–99%) and Utqiaġvik (86–89%), with minor contributions from fossil sources. Periods of significantly elevated PM, TC, OC, and EC concentrations coincided with major boreal forest fire activity in North America that brought smoke to the region. The radiocarbon signature of EC measured at Toolik during these wildfire smoke events indicated that over 90% of the EC originated from modern sources. Our measurements demonstrate changing aerosol concentrations in the Arctic during the summer, and emphasize the need for continuous atmospheric monitoring to evaluate and advance our understanding of this rapidly changing atmospheric environment. (Manuscript in prep) 

Fossil fuel carbon dioxide emissions (ffCO2) constitute the majority of greenhouse gas emissions and are the main determinent of global climate change. The COVID-19 pandemic caused wide-scale disruption to human activity and provided an opportunity to evaluate our capability to detect ffCO2 emission reductions. Quantifying changes in ffCO2 levels is especially challenging in cities, where climate mitigation policies are being implemented but local emissions lead to spatially and temporally complex atmospheric mixing ratios. Here, we used direct observations of on-road CO2 mixing ratios with analyses of the radiocarbon (14C) content of annual grasses collected by community scientists in Los Angeles and California, USA to assess reductions in ffCO2 emissions during the first two years of the COVID-19 pandemic. With COVID-19 mobility restrictions in place in 2020, we observed a significant reduction in ffCO2 levels across California, especially in urban centers. In Los Angeles, CO2 enhancements on freeways were 60 ± 16% lower and ffCO2 levels were 38-52% lower than in pre-pandemic years. By 2021, California's ffCO2 levels rebounded to pre-pandemic levels, albeit with substantial spatial heterogeneity related to local and regional pandemic measures. Taken together, our results indicate that a reduction in traffic emissions by ~60% (or 10-24% of Los Angeles' total ffCO2 emissions) can be robustly detected by plant 14C analysis, and pave the way for mobile- and plant-based monitoring of ffCO2 emissions in cities without CO2 monitoring infrastructure such as those in the Global South. 

Abstract Development can play a critical role in how organisms respond to changes in the environment. Tolerance to environmental challenges can vary during ontogeny, with individual- and population-level impacts that are associated with the timing of exposure relative to the timing of vulnerability. In addition, the life history consequences of different stressors can vary with the timing of exposure to stress. Salinization of freshwater ecosystems is an emerging environmental concern, and habitat salinity can change rapidly due, for example, to storm surge, runoff of road deicing salts, and rainfall. Elevated salinity can increase the demands of osmoregulation in freshwater organisms, and amphibians are particularly at risk due to their permeable skin and, in many species, semi-aquatic life cycle. In three experiments, we manipulated timing and duration of exposure to elevated salinity during larval development of southern toad (Anaxyrus terrestris) tadpoles and examined effects on survival, larval growth, and timing of and size at metamorphosis. Survival was reduced only for tadpoles exposed to elevated salinity early in development, suggesting an increase in tolerance as development proceeds; however, we found no evidence of acclimation to elevated salinity. Two forms of developmental plasticity may help to ameliorate costs of transient salinity exposure. With early salinity exposure, the return to freshwater was accompanied by a period of rapid compensatory growth, and metamorphosis ultimately occurred at a similar age and size as freshwater controls. By contrast, salinity exposure later in development led to earlier metamorphosis at reduced size, indicating an acceleration of metamorphosis as a mechanism to escape salinity stress. Thus, the consequences of transient salinity exposure were complex and were mediated by developmental state. Salinity stress experienced early in development resulted in acute costs but little long-lasting effect on survivors, while exposures later in development resulted in sublethal effects that could influence success in subsequent life stages. Overall, our results suggest that elevated salinity is more likely to affect southern toad larvae when experienced early during larval development, but even brief sublethal exposure later in development can alter life history in ways that may impact fitness. 

Abstract Warming climate in the Arctic is leading to an increase in isoprene emission from ecosystems. We assessed the influence of temperature on isoprene emission from Arctic willows with laboratory and field measurements. Our findings indicate that the hourly temperature response curve ofSalixspp., the dominant isoprene emitting shrub in the Arctic, aligns with that of temperate plants. In contrast, the isoprene capacity of willows exhibited a more substantial than expected response to the mean ambient temperature of the previous day, which is much stronger than the daily temperature response predicted by the current version of the Model of Emissions of Gases and Aerosols from Nature (MEGAN). With a modified algorithm from this study, MEGAN predicts 66% higher isoprene emissions for Arctic willows during an Arctic heatwave. However, despite these findings, we are still unable to fully explain the high temperature sensitivity of isoprene emissions from high latitude ecosystems.