Anaerobic digestion is a bioenergy technology that can play a vital role in achieving net-zero emissions by converting organic matter into biomethane and biogenic carbon dioxide. By implementing bioenergy with carbon capture and storage (BECCS), carbon dioxide can be separated from biomethane, captured, and permanently stored, thus generating carbon dioxide removal (CDR) to offset hard-to-abate emissions. Here, we quantify the global availability of waste biomass for BECCS and their CDR and biomethane technical potentials. These biomass feedstocks do not create additional impacts on land, water, and biodiversity and can allow a more sustainable development of BECCS while still preserving soil fertility. We find that up to 1.5 Gt CO2 per year, or 3% of global GHG emissions, are available to be deployed for CDR worldwide. The conversion of waste biomass can generate up to 10 700 TWh of bioenergy per year, equivalent to 10% of global final energy consumption and 27% of global natural gas supply. Our assessment quantifies the climate mitigation potential of waste biomass and its capacity to contribute to negative emissions without relying on extensive biomass plantations.

Trait differences between invasive plants and the plants in their recipient communities moderate the impact of invaders on community composition. Callery pear (Pyrus calleryana Decne.) is a fast-growing, stress-tolerant tree native to China that has been widely planted for its ornamental value. In recent decades, P. calleryana has naturalized throughout the eastern United States, where it spreads rapidly and achieves high abundance in early-successional environments. Here we compare the impacts of low-density, establishment-phase P. calleryana to those of functionally similar native trees on the understory community diversity and total cover of three early-successional meadows in Indiana's Eastern Corn Belt Plains. In contrast to our prediction that P. calleryana would have greater negative effects on the total abundance and diversity of the understory plant community compared with native tuliptree (Liriodendron tulipifera L.), American sycamore (Platanus occidentalis L.), or non-tree control plots, we found that these low-density populations of P. calleryana had no significant impact on total cover, species richness, or diversity indices for the understory community compared with the native trees and non-tree control plots. Likewise, the studied populations of P. calleryana had no significant impact on the native, introduced, woody, or native tree subsets of the understory community. These results indicate that in young, low-density populations situated in early-successional meadows, the trait differences between P. calleryana and functionally similar native trees are not of a great enough magnitude to produce changes in community composition. Going forward, complementary research on the impacts of P. calleryana on community composition and ecosystem processes in areas with long-established, dense invasions or invasions in more sensitive ecosystems would allow us to more fully understand how this widespread invader disrupts its host ecosystems.

We present a spectroscopic analysis of Eridanus IV (Eri IV) and Centaurus I (Cen I), two ultrafaint dwarf galaxies of the Milky Way. Using IMACS/Magellan spectroscopy, we identify 28 member stars of Eri IV and 34 member stars of Cen I. For Eri IV, we measure a systemic velocity of vsys=-31.5-1.2+1.3kms-1 , and velocity dispersion sigma v=6.1-0.9+1.2kms-1 . Additionally, we measure the metallicities of 16 member stars of Eri IV. We find a metallicity of [Fe/H]=-2.87-0.07+0.08 , and resolve a dispersion of sigma [Fe/H]=0.20 +/- 0.09. The mean metallicity is marginally lower than all other known ultrafaint dwarf galaxies, making it one of the most metal-poor galaxies discovered thus far. Eri IV also has a somewhat unusual right-skewed metallicity distribution. For Cen I, we find a velocity v sys = 44.9 +/- 0.8 km s-1, and velocity dispersion sigma v=4.2-0.5+0.6kms-1 . We measure the metallicities of 27 member stars of Cen I, and find a mean metallicity [Fe/H] = -2.57 +/- 0.08, and metallicity dispersion sigma[Fe/H]=0.38-0.05+0.07 . We calculate the systemic proper motion, orbit, and the astrophysical J-factor for each system, the latter of which indicates that Eri IV is a good target for indirect dark matter detection. We also find no strong evidence for tidal stripping of Cen I or Eri IV. Overall, our measurements confirm that Eri IV and Cen I are dark-matter-dominated galaxies with properties largely consistent with other known ultrafaint dwarf galaxies. The low metallicity, right-skewed metallicity distribution, and high J-factor make Eri IV an especially interesting candidate for further follow-up.

We present high-cadence ultraviolet through near-infrared observations of the Type Ia supernova (SN Ia) 2023bee at D = 32 +/- 3 Mpc, finding excess flux in the first days after explosion, particularly in our 10 minutes cadence TESS light curve and Swift UV data. Compared to a few other normal SNe Ia with early excess flux, the excess flux in SN 2023bee is redder in the UV and less luminous. We present optical spectra of SN 2023bee, including two spectra during the period where the flux excess is dominant. At this time, the spectra are similar to those of other SNe Ia but with weaker Si ii, C ii, and Ca ii absorption lines, perhaps because the excess flux creates a stronger continuum. We compare the data to several theoretical models on the origin of early excess flux in SNe Ia. Interaction with either the companion star or close-in circumstellar material is expected to produce a faster evolution than observed. Radioactive material in the outer layers of the ejecta, either from double detonation explosion or from a 56Ni clump near the surface, cannot fully reproduce the evolution either, likely due to the sensitivity of early UV observable to the treatment of the outer part of ejecta in simulation. We conclude that no current model can adequately explain the full set of observations. We find that a relatively large fraction of nearby, bright SNe Ia with high-cadence observations have some amount of excess flux within a few days of explosion. Considering potential asymmetric emission, the physical cause of this excess flux may be ubiquitous in normal SNe Ia.

We examine the sensitivity of the seasonal cycle of heterotrophic respiration to model estimates of litterfall seasonality, herbivory, plant allocation, tissue chemistry, and land use. As a part of this analysis, we compare heterotrophic respiration models based solely on temperature and soil moisture controls (zero-order models) with models that depend on available substrate as well (first-order models). As indicators of regional and global CO2 exchange, we use maps of monthly global net ecosystem production, growing season net flux (GSNF), and simulated atmospheric CO2 concentrations from an atmospheric tracer transport model. In one first-order model, CASA, variations on the representation of the seasonal flow of organic matter from plants to heterotrophs can increase global GSNF as much as 60% (5.7 Pg C yr(-1)) above estimates obtained from a zero-order model. Under a new first-order scheme that includes separate seasonal dynamics for leaf litterfall, fine root mortality, coarse woody debris, and herbivory, we observe an increase in GSNF of 8% (0.7 Pg C yr(-1)) over that predicted by the zero-order model. The increase in seasonality of CO2 exchange in first-order models reflects the dynamics of labile litter fractions; specifically, the rapid decomposition of a pulse of labile leaf and fine root litter that enters the heterotrophic community primarily from the middle to the end of the growing season shifts respiration outside the growing season. From the perspective of a first-order model, we then explore the consequences of land use change and winter temperature anomalies on the amplitude of the seasonal cycle of atmospheric CO2. Agricultural practices that accelerate decomposition may drive a long-term increase in the amplitude, independent of human impacts on plant production. Consideration of first-order litter decomposition dynamics may also help explain year-to-year variation in the amplitude.

In recent years, the chief approaches used to describe the terrestrial carbon sink have been either (1) inferential, based on changes in the carbon content of the atmosphere and other elements of the global carbon cycle, or (2) mechanistic, applying our knowledge of terrestrial ecology to ecosystem scale processes. In this study, the two approaches are integrated by determining the change in terrestrial properties necessary to match inferred change in terrestrial carbon storage. In addition, a useful mathematical framework is developed for understanding the important features of the terrestrial carbon sink. The Carnegie-Ames-Stanford Approach (CASA) biosphere model, a terrestrial carbon cycle model that uses a calibrated, semimechanistic net primary production model and a mechanistic plant and soil carbon turnover model, is employed to explore carbon turnover dynamics in terms of the specific features of terrestrial ecosystems that are most important for the potential development of a carbon sink and to determine the variation in net primary production (NPP) necessary to satisfy various carbon sink estimates. Given the existence of a stimulatory mechanism acting on terrestrial NPP, net ecosystem uptake is expected to be largest where NPP is high and the turnover of carbon through plants and the soil is slow. In addition, it was found that (1) long-term, climate-induced change in heterotrophic respiration is not as important in determining long-term carbon exchange as is change in NPP and (2) the terrestrial carbon sink rate is determined not by the cumulative increase in production over some pre-industrial baseline, but rather by the rate of increase in production over the industrial period.