Unusually large peak electron density values of ∼5 × 1010 m−3 are sporadically observed in the nightside ionosphere of Mars in regions of strong and open crustal magnetic field. However, the associated vertical structure of the ionosphere has not previously been observed. Here, we present three vertical electron density profiles from the nightside ionosphere of Mars that have comparably large values of peak electron density. They were acquired by the Radio Occultation Science Experiment on the MAVEN spacecraft on 23, 24, and 29 March 2021. In these profiles, the peak density is large (2–4 × 1010 m−3), the peak altitude is low (60–90 km), and the plasma layer is broad (full width at half maximum greater than 100 km, Chapman layer lengthscale of ∼30 km). Even if the peak altitude is at the upper end of this range, 90 km, the plasma density at 60 km would still be large, approximately 70% of the peak density. These findings hold even if the ionosphere was patchy, not spherically symmetric, during these observations. These three profiles were acquired at times when fluxes of energetic protons, but not electrons, were enhanced above background levels. The apparent association of large nightside electron density values with protons, rather than electrons, is contrary to previous findings.

To complement Hisaki's ultraviolet monitoring of the Io plasma torus, a ground‐based campaign assembled a comprehensive data set at visible wavelengths with the ARC 3.5‐m telescope at Apache Point Observatory. This work concentrates on the bright S + emissions in these data. Recurrent traits in the intensity and location are discerned as a function of Jovian longitude (λ III ). The longitudinal brightness structure differs from past data sets in the visible but is broadly consistent with that of Io's auroral footprint and concurrent Hisaki extreme ultraviolet measurements. Positions of the ribbon feature with λ III confirm that it exhibits a radial wobbling motion that is lesser than the centrifugal limit along a given L‐shell. We also find that the radial separation between the cold torus and the ribbon is modulated as Jupiter rotates. The torus is displaced 0.13 R J dawnward, on average, by an electric field with mean strength 3.8 mV/m, consistent with that inferred by analysis of Hisaki's dawn‐dusk brightness asymmetry. The lesser visible brightness asymmetry is uncorrelated to this field strength, however. S + emissions are enhanced downstream of Io, principally at Jovian dawn. Io interacts with the densest region at specific Jovian longitudes and local times; near λ III ~130° and dawn the ribbon is farthest from Jupiter but still passes radially interior to the satellite. The electron density sweeping past Io and/or its radial proximity to the passing ribbon may also influence brightness, but S + emissions are not governed by a single predominant driver.

Raw sequence data for research submitted to Elementa on the microbial community associated with isoprene consumption in soils. Included are GNU Zip files of I1, R1 and R2 files from an Illumina MySeq run using 16S and ITS primers. These files were seperated due to size and therefore must be placed back together before any processing. Files with parentheses indicate the numbered piece of the whole file. Also included are the two mapping files that translate the barcoded region of the sequence to a sample identifier.

Abstract Isoprene is a reactive volatile organic compound released from the biosphere that can be abundant in the planetary boundary layer, where it can have a myriad of effects on atmospheric chemistry and secondary aerosol formation. There is currently a high degree of uncertainty in forecasts of how atmospheric isoprene concentrations will shift in response to anthropogenic land-use change and climate change. One source of this uncertainty is that studies of terrestrial isoprene fluxes have almost entirely focused on plant sources of isoprene, largely ignoring the role of soils as a sink of isoprene and the corresponding microbial consumption of isoprene. We quantified isoprene consumption rates by the microbial communities found in two distinct soils under laboratory conditions and used high-throughput sequencing to identify the bacterial and fungal taxa that increased in relative abundance with changes in isoprene mixing ratios. On average, soil microbes were capable of consuming 68% (ranging 55% to 80%) of the gaseous isoprene provided to the soils (2–200 ppbv) in a flow-through experiment. Consumption rates increased with increasing levels of isoprene with rates reaching 770 pmol g-1 h-1 in one of the soils exposed to the highest mixing ratio of isoprene (200 ppbv). Increases in isoprene levels were associated with significant shifts in the composition of both soil bacterial and fungal communities. A wide range of taxa were associated with isoprene consumption including members of the Actinobacteria, Proteobacteria, Gemmatimonadetes, and Zygomycota phyla with many of the taxa being closely related to known hydrocarbon degraders. Soils likely represent a significant sink of atmospheric isoprene and our results suggest that a wide range of bacterial and fungal taxa are capable of isoprene degradation.

Nonmethane biogenic volatile organic compounds (BVOCs) play key roles in the atmosphere, where they can influence a wide range of chemical processes, and in soils, where they can alter the rates of biogeochemical cycles and impact the growth of plants and soil organisms. However, the diversity and quantities of BVOCs released from or taken up by soils remain poorly characterized as do the biotic and abiotic controls on these fluxes. Here we used proton transfer reaction mass spectrometry to quantify BVOC flux rates from soils with and without active root systems in a subalpine coniferous forest. The total measured BVOC flux averaged 102nmolm(-2)h(-1) (an estimated 2.0 mu g-C m(-2)h(-1)). The individual BVOCs with the highest net emissions from soil included monoterpenes and methanol (averaging 646 and 641ng-C m(-2)h(-1), respectively) while soil represented a net sink of isoprene (-98ng-C m(-2)h(-1)) and formaldehyde (-37ng-C m(-2)h(-1)). Tree roots, directly or indirectly, contributed an average of 53% of the total carbon emitted from the soil as BVOCs, with methanol and acetaldehyde among those BVOCs most strongly associated with active root presence. The fluxes of most of the dominant BVOCs emitted from soil, including methanol, increased linearly with increasing temperature. Together the fluxes of certain BVOCs into or out of the forest floor (particularly methanol, isoprene, and monoterpenes) are likely relevant to ecosystem-level processes and belowground ecology, but these fluxes are highly variable and are strongly controlled by both root presence and soil abiotic conditions.

Nonmethane volatile organic compounds (VOCs) are reactive, low molecular weight gases that can have significant effects on soil and atmospheric processes. Research into biogenic VOC sources has primarily focused on plant emissions, with few studies on VOC emissions from decomposing plant litter, another potentially important source. Likewise, although there have been numerous studies examining how anthropogenic increases in nitrogen (N) availability can influence litter decomposition rates, we do not know how VOC emissions may be affected. In this study, we measured the relative contribution of VOCs to the total carbon (C) emitted from decomposing litter and how N amendments affected VOC emissions. We incubated decomposing litter from 12 plant species over 125 similar to days, measuring both CO2 and VOC emissions throughout the incubation. We found that VOCs represented a large portion of C emissions from a number of the litter types with C emissions as VOCs ranging from 0% to 88% of C emissions as CO2. Methanol was the dominant VOC emitted, accounting for 2899% of total VOC emissions over the incubation period. N additions increased CO2 production in 7 of the 12 litter types by 5180%. In contrast, N additions decreased VOC emissions in 8 of the 12 litter types, reducing net VOC emissions to near zero. The decrease in VOC emissions was occasionally large enough to account for the increased CO2 emissions on a per unit C basis, suggesting that N additions may not necessarily accelerate C loss from decomposing litter but rather just switch the form of C emitted. Together these results suggest that, for certain litter types, failure to account for VOC emissions may lead to an underestimation of C losses from litter decomposition and an overestimation of the effects of N additions on rates of litter decomposition.

Volatile organic compounds (VOCs) are emitted during plant litter decomposition, and such VOCs can have wide‐ranging impacts on atmospheric chemistry, terrestrial biogeochemistry, and soil ecology. However, we currently have a limited understanding of the relative importance of biotic versus abiotic sources of these VOCs and whether distinct types of litter emit different types and quantities of VOCs during decomposition. We analyzed VOCs emitted by microbes or by abiotic mechanisms during the decomposition of litter from 12 plant species in a laboratory experiment using proton transfer reaction mass spectrometry (PTR‐MS). Net emissions from litter with active microbial populations (non‐sterile litters) were between 0 and 11 times higher than emissions from sterile controls over a 20‐d incubation period, suggesting that abiotic sources of VOCs are generally less important than biotic sources. In all cases, the sterile and non‐sterile litter treatments emitted different types of VOCs, with methanol being the dominant VOC emitted from litters during microbial decomposition, accounting for 78 to 99% of the net emissions. We also found that the types of VOCs released during biotic decomposition differed in a predictable manner among litter types with VOC profiles also changing as decomposition progressed over time. These results show the importance of incorporating both the biotic decomposition of litter and the species‐dependent differences in terrestrial vegetation into global VOC emission models.