Photosynthesis - the conversion of energy from sunlight into chemical energy - is essential for life on Earth. Yet there is much we do not understand about photosynthetic energy conversion on a fundamental level: how it evolved and the extent of its diversity, its dynamics, and all the components and connections involved in its regulation. In this commentary, researchers working on fundamental aspects of photosynthesis including the light-dependent reactions, photorespiration, and C4 photosynthetic metabolism pose and discuss what they view as the most compelling open questions in their areas of research.

Motivation: The study of bacterial genome dynamics is vital for understanding the mechanisms underlying microbial adaptation, growth, and their impact on host phenotype. Structural variants (SVs), genomic alterations of 50 base pairs or more, play a pivotal role in driving evolutionary processes and maintaining genomic heterogeneity within bacterial populations. While SV detection in isolate genomes is relatively straightforward, metagenomes present broader challenges due to the absence of clear reference genomes and the presence of mixed strains. In response, our proposed method rhea, forgoes reference genomes and metagenome-assembled genomes (MAGs) by encompassing all metagenomic samples in a series (time or other metric) into a single co-assembly graph. The log fold change in graph coverage between successive samples is then calculated to call SVs that are thriving or declining.Results: We show rhea to outperform existing methods for SV and horizontal gene transfer (HGT) detection in two simulated mock metagenomes, particularly as the simulated reads diverge from reference genomes and an increase in strain diversity is incorporated. We additionally demonstrate use cases for rhea on series metagenomic data of environmental and fermented food microbiomes to detect specific sequence alterations between successive time and temperature samples, suggesting host advantage. Our approach leverages previous work in assembly graph structural and coverage patterns to provide versatility in studying SVs across diverse and poorly characterized microbial communities for more comprehensive insights into microbial gene flux.Availability and implementation: rhea is open source and available at: https://github.com/treangenlab/rhea.

Microbial mats are stratified communities often dominated by unicellular and filamentous phototrophs within an exopolymer matrix. It is challenging to quantify the dynamic responses of community members in situ as they experience steep gradients and rapid fluctuations of light. To address this, we developed a binary consortium using two representative isolates from hot spring mats, the unicellular oxygenic phototrophic cyanobacterium Synechococcus OS-B' (Syn OS-B') and the filamentous anoxygenic phototroph Chloroflexus MS-CIW-1 (Chfl MS-1). We quantified the motility of individual cells and entire colonies and demonstrated that Chfl MS-1 formed bundles of filaments that moved in all directions with no directional bias to light. Syn OS-B' was slightly less motile but exhibited positive phototaxis. This binary consortium displayed cooperative behavior by moving further than either species alone and formed ordered arrays where both species aligned with the light source. No cooperative motility was observed when a non-motile pilB mutant of Syn OS-B' was used instead of Syn OS-B'. The binary consortium also produced more adherent biofilm than individual species, consistent with the close interspecies association revealed by electron microscopy. We propose that cyanobacteria and Chloroflexota cooperate in forming natural microbial mats, by colonizing new niches and building robust biofilms.

Ukraine supplies a large proportion of grain and oilseeds to the world market and faces disruptions from the Russian invasion in 2022. Here we explore the combined effects of the invasion and climate change on Ukraine's irrigation. In 2021, only 1.6% of Ukraine's cropland was irrigated. Of this portion, 73% experienced substantial declines in irrigated crop production following the invasion. We estimate that by the mid-twenty-first century, three-quarters of croplands will experience water shortages, making business-as-usual rain-fed agricultural practices inadequate in addressing the challenges posed by climate change. We explore how leveraging local surface and groundwater resources could enable sustainable irrigation expansion over 18 million hectares of croplands and form a viable climate adaptation strategy. Finally, we identify regions for implementing enhancements or expansions of irrigation systems that can foster a more resilient agricultural sector-underscoring the growing importance of irrigation in sustaining crop production in Ukraine.

Understanding the climate and carbon cycle response to negative CO2 emissions is important for developing climate mitigation strategies that aim to limit global warming to a specific threshold. In this study, using a coupled climate and carbon cycle model, a novel set of nine stylized simulations are conducted with cumulative emissions of 1,000 GtC, 2,000 GtC, and 5,000 GtC over 150, 250, and 500 years, followed by identical cumulative negative emissions so that the net cumulative emissions are zero. On millennial-timescales, the climate system returns close to the preindustrial state, independent of the emission and removal pathways. However, the thermal and biogeochemical inertia of the ocean play an important role in determining the climate and carbon cycle response during the emission and removal phases. When zero net emissions are reached, surface air temperature is larger by 0-1 degrees C than the preindustrial state, and the atmospheric CO2 concentration is less by 12-29 ppm. These changes increase with both the magnitude and duration of the emission and removal pulses. In contrast, hysteresis in the relationship between global mean surface temperature and cumulative carbon emissions increases with the magnitude but decreases with the duration of emission and removal pulses. Our study highlights the role of ocean inertia in the asymmetry in climate response to emissions and removals and indicates that an earlier emission reduction implying emission/removal pathways with smaller magnitudes and shorter durations for the positive and negative emission pulses would avoid larger climate and carbon cycle impacts on centennial-timescales.

We present an analysis of Type Ia supernovae (SNe Ia) from the Carnegie Supernova Project I and II and extend the Hubble diagram from optical to near-infrared wavelengths (uBgVriYJH). We calculate the Hubble constant, H 0, using various distance calibrators: Cepheids, the tip of the red giant branch (TRGB), and surface brightness fluctuations (SBFs). Combining all methods of calibration, we derive H 0 = 71.76 +/- 0.58 (stat) +/- 1.19 (sys) km s(-1) Mpc(-1) from the B band and H 0 = 73.22 +/- 0.68 (stat) +/- 1.28 (sys) km s(-1) Mpc(-1) from the H band. By assigning equal weight to the Cepheid, TRGB, and SBF calibrators, we derive the systematic errors required for consistency in the first rung of the distance ladder, resulting in a systematic error of 1.2 similar to 1.3 km s(-1) Mpc(-1) in H 0. As a result, relative to the statistics-only uncertainty, the tension between the late-time H 0 we derive by combining the various distance calibrators and the early-time H 0 from the cosmic microwave background is reduced. The highest precision in SN Ia luminosity is found in the Y band (0.12 +/- 0.01 mag), as defined by the intrinsic scatter (sigma int). We revisit SN Ia Hubble residual-host mass correlations and recover previous results that these correlations do not change significantly between the optical and near-infrared wavelengths. Finally, SNe Ia that explode beyond 10 kpc from their host centers exhibit smaller dispersion in their luminosity, confirming our earlier findings. A reduced effect of dust in the outskirts of hosts may be responsible for this effect.

Among Neptunian mass exoplanets (20-50 M-circle plus), puffy hot Neptunes are extremely rare, and their unique combination of low mass and extended radii implies very low density (rho < 0.3 g cm(-3)). Over the last decade, only a few puffy planets have been detected and precisely characterized with both transit and radial velocity observations, most notably including WASP-107 b, TOI-1420 b, and WASP-193 b. In this paper, we report the discovery of TOI-1173 A b, a low-density ( rho=0.195-0.017+0.018 g cm(-3)) super-Neptune with P = 7.06 days in a nearly circular orbit around the primary G-dwarf star in the wide binary system TOI-1173 A/B. Using radial velocity observations with the MAROON-X and HIRES spectrographs and transit photometry from TESS, we determine a planet mass of M p = 27.4 +/- 1.7 M circle plus and radius of R p = 9.19 +/- 0.18 R circle plus. TOI-1173 A b is the first puffy super-Neptune planet detected in a wide binary system (projected separation similar to 11,400 au). We explore several mechanisms to understand the puffy nature of TOI-1173 A b and show that tidal heating is the most promising explanation. Furthermore, we demonstrate that TOI-1173 A b likely has maintained its orbital stability over time and may have undergone von-Zeipel-Lidov-Kozai migration followed by tidal circularization, given its present-day architecture, with important implications for planet migration theory and induced engulfment into the host star. Further investigation of the atmosphere of TOI-1173 A b will shed light on the origin of close-in low-density Neptunian planets in field and binary systems, while spin-orbit analyses may elucidate the dynamical evolution of the system.

We present Augustus, a catalog of distance, extinction, and stellar parameter estimates for 170 million stars from 14 mag < r < 20 mag and with divided by b divided by > 10 degrees drawing on a combination of optical to near-infrared photometry from Pan-STARRS, 2MASS, UKIDSS, and unWISE along with parallax measurements from Gaia DR2 and 3D dust extinction maps. After applying quality cuts, we find 125 million objects have "high-quality" posteriors with statistical distance uncertainties of less than or similar to 10% for objects with well-constrained stellar types. This is a substantial improvement over the distance estimates derived from Gaia parallaxes alone and in line with the recent results from Anders et al. We find the fits are able to reproduce the dereddened Gaia color-magnitude diagram accurately, which serves as a useful consistency check of our results. We show that we are able to detect large, kinematically coherent substructures in our data clearly relative to the input priors, including the Monoceros Ring and the Sagittarius Stream, attesting to the quality of the catalog. Our results are publicly available at doi:10.7910/DVN/WYMSXV. An accompanying interactive visualization can be found at http://allsky.s3-website.us-east-2.amazonaws.com.

Leaf carbon isotope ratios and leaf mineral composition (Ca, K, Mg, Mn, N, and P) were measured on the dominant species along an irradiance cline in a subtropical monsoon forest of southern China. This irradiance cline resulted from disturbance caused by fuel-harvesting. Leaf carbon isotope ratios increased from undisturbed to disturbed sites for all species, indicating that leaf intercellular CO2 concentrations decreased and leaf water use efficiencies increased along this cline. Nitrogen and magnesium levels were lower in leaves of species on the disturbed sites, but there were no clear patterns for calcium, potassium, phosphorus or manganese.

Carbon isotope ratios were used to survey the distribution of photosynthetic pathways among taxa, the relationship between photosynthetic pathway and habitat light levels, and the relationship between intercellular CO2 levels of C3 plants and habitat light levels within a subtropical monsoon forest in southern China. Of 128 species, most (94) possessed the C3 photosynthetic pathway; 33 species possessed the C4 pathway and all of these were restricted to high light locations. There was one epiphytic CAM species. The C3 species were classified as occurring in open, intermediate, and closed canopy sites. Among C3 species, carbon isotope ratios tended to become more negative with decreasing light availability in the habitat.