Carbon Loss Research Articles

Repeat GEDI footprints measure the effects of tropical forest disturbances

More of the Amazon rainforest is disturbed each year than completely deforested, but the impact of these disturbances on the carbon cycle remains poorly understood. Recent algorithmic advances using optical and radar remote sensing have improved detection of disturbances at fine spatiotemporal resolution, but quantifying changes in forest structure and biomass associated with these detected disturbances has proven challenging. The Global Ecosystem Dynamics Investigation (GEDI), a spaceborne lidar mission collecting data from 2019 to 2023, provides an opportunity to address this problem. GEDI captured billions of measurements of forest height, plant area, and understory structure within ∼25-m diameter footprints scattered across the tropics. Though the instrument had no guaranteed repeat cycle, it sometimes sampled nearby locations twice; some of these spatially near-coincident footprints happened to measure forest structure before and after a detected disturbance, providing information on how disturbance affected aboveground biomass. In this study, we developed an efficient general-purpose open-source pipeline for identifying spatially coincident footprints, which is a computationally complex task, and used the pipeline to find over 13,700 footprint pairs with intervening disturbance events across the Amazon biome. We also identified a set of ∼65,000 spatially near-coincident footprint pairs that lacked an intervening disturbance but came from regions with similar disturbance threat; these provided a control dataset to evaluate the effectiveness of estimating forest structure and biomass changes with nearby footprints. Analysis of this Amazon-wide dataset demonstrated that GEDI was able to measure statistically significant canopy height and biomass deficits following non-stand-replacing disturbances as small as 900 m2 (30 m × 30 m). GEDI's unique three-dimensional view of forest structure also reflected the effects of different intensities of fire disturbance, including 20% of burned areas where the upper canopy retained most of its height, but the understory suffered substantial foliage losses. Finally, we modeled the relationship between Landsat and Sentinel-1 disturbance detection parameters and GEDI-estimated percent biomass loss, showing that certain satellite-derived intensity metrics are correlated with increasing biomass loss and identifying temporal trends in biomass loss and recovery following disturbance. This work represents an important step towards the development of a pan-tropical, spatially explicit system for tracking carbon losses and structural changes arising from forest disturbance.

Incorporating leys in arable systems as a mitigation strategy to reduce soil organic carbon losses during land-use change

Incorporating leys in arable systems as a mitigation strategy to reduce soil organic carbon losses during land-use change

Use of a mixture design to optimize dietary macronutrients for large turbot (Scophthalmus maximus Linnaeus, 1758)

Aim of study: Studies on the dietary needs of turbot fish (Scophthalmus maximus Linnaeus, 1758) have largely focused on the juvenile stage; however, there are not many on the larger (300–500 g) species. The purpose of this experiment was to determine the ideal dietary levels of protein, fat, and carbohydrate for large turbot. Area of study: Demre, Antalya, Türkiye. Material and methods: A three-component mixture design model was created to adjust the quantities of dietary protein between 45.6% and 63.4%, carbohydrates between 4.9% and 30.5%, and fat between 5.6% and 17.7%. The components of the model were fish meal (FM), fish oil (FO), and wheat flour (W). Fish initially weighing 301.6±0.1 g on average were fed 14 different diets for 10 weeks. The ideal dietary macronutrient levels were estimated by examining the prediction profiler at the highest desirability based on the variables that were selected to maximize final weight, daily growth coefficient, protein efficiency ratio, nitrogen and energy retentions, and minimize feed conversion ratio, nitrogen and carbon losses. Main results: The optimal diet formulation yielded the highest desirability of 0.87 for all selected responses and resulted in dietary inclusion levels of FM, W and FO as 63.6%, 20.8%, and 9.4%, respectively. The proposed optimal nutrient concentrations for large turbot (growing from 300 to 500 g) are 54% protein, approximately 17% lipid, and 15.8% carbohydrate on dry matter basis. Research highlights: The mixture design successfully allowed us to estimate the optimum levels of dietary protein, lipid and carbohydrate for large turbot.

Conversion of boreal forests to agricultural systems: soil microbial responses along a land-conversion chronosequence

BackgroundBoreal regions are warming at more than double the global average, creating opportunities for the northward expansion of agriculture. Expanding agricultural production in these regions will involve the conversion of boreal forests to agricultural fields, with cumulative impacts on soil microbial communities and associated biogeochemical cycling processes. Understanding the magnitude or rate of change that will occur with these biological processes will provide information that will enable these regions to be developed in a more sustainable manner, including managing carbon and nitrogen losses. This study, based in the southern boreal region of Canada where agricultural expansion has been occurring for decades, used a paired forest-adjacent agricultural field approach to quantify how soil microbial communities and functions were altered at three different stages post-conversion (< 10, > 10 and < 50, and > 50 years). Soil microbial functional capacity was assessed by quantitative PCR of genes associated with carbon (C), nitrogen, and phosphorous (P) cycling; microbial taxonomic diversity and community structure was assessed by amplicon sequencing.ResultsFungal alpha diversity did not change, but communities shifted from Basidiomycota to Ascomycota dominant within the first decade. Bacterial alpha diversity increased, with Gemmatimonadota groups generally increasing and Actinomycetota groups generally decreasing in agricultural soils. These altered communities led to altered functional capacity. Functional genes associated with nitrification and low molecular weight C cycling potential increased after conversion, while those associated with organic P mineralization potential decreased. Stable increases in most N cycling functions occurred within the first decade, but C cycling functions were still changing 50 years post conversion.ConclusionsMicrobial communities underwent a rapid shift in the first decade, followed by several decades of slower transition until stabilizing 50 years post conversion. Understanding how the microbial communities respond at different stages post-conversion improves our ability to predict C and N losses from emerging boreal agricultural systems, and provides insight into how best to manage these soils in a way that is sustainable at the local level and within a global context.

Improving Crop Yield through Increasing Carbon Gain and Reducing Carbon Loss.

Photosynthesis is a process where solar energy is utilized to convert atmospheric CO2 into carbohydrates, which forms the basis for plant productivity. The increasing demand for food has created a global urge to enhance yield. Earlier, the plant breeding program was targeting the yield and yield-associated traits to enhance the crop yield. However, the yield cannot be further improved without improving the leaf photosynthetic rate. Hence, in this review, various strategies to enhance leaf photosynthesis were presented. The most promising strategies were the optimization of Rubisco carboxylation efficiency, the introduction of a CO2 concentrating mechanism in C3 plants, and the manipulation of photorespiratory bypasses in C3 plants, which are discussed in detail. Improving Rubisco's carboxylation efficiency is possible by engineering targets such as Rubisco subunits, chaperones, and Rubisco activase enzyme activity. Carbon-concentrating mechanisms can be introduced in C3 plants by the adoption of pyrenoid and carboxysomes, which can increase the CO2 concentration around the Rubisco enzyme. Photorespiration is the process by which the fixed carbon is lost through an oxidative process. Different approaches to reduce carbon and nitrogen loss were discussed. Overall, the potential approaches to improve the photosynthetic process and the way forward were discussed in detail.

Maximizing the value of liquid products and minimizing carbon loss in hydrothermal processing of biomass: an evolution from carbonization to humification

Hydrothermal carbonization (HTC) converts wet biomass into hydrochar and a process liquid, but aromatic compounds in the products have been reported as a roadblock for soil applications as they can inhibit germination, plant growth, and soil microbial activity. Here, we compared HTC and hydrothermal humification (HTH) of cow manure digestate while varying the initial alkaline content by adding KOH. HTH converted 37.5 wt% of the feedstock to artificial humic acids (A-HAs) found in both solid and liquid, twice that of HTC. HTH reduced phenolic and furanic aromatic compounds by over 70% in solids and 90% in liquids. The A-HAs in HTH resemble natural humic acids (N-HA), based on FTIR, UV–vis spectra, and CHN and XRD analysis. The HTH liquid possesses 60% higher total organic carbon (TOC) than HTC. Although one-third of TOC can be precipitated as A-HA, a high TOC concentration remains in the liquid, which is shown to be mainly organic acids. Therefore, we also evaluated the HTC and HTH liquids for anaerobic biomethane production, and found that compared to the original cow manure digestate, the HTH liquids increased methane yield by 110.3 to 158.6%, a significant enhancement relative to the 17.2% increase seen with HTC liquid. The strong reduction in organic acids during biogas production from HTH liquid indicates the potential for converting soluble byproducts into methane, while maintaining high A-HAs levels in the solid product.Graphical

Leguminous forage introduction and returning reduced soil inorganic carbon loss on the Loess Plateau

Despite evidence from experiments that no-till and stubble retention promote soil organic carbon accumulation, it is not yet clear if this is the case for soil inorganic carbon (SIC), particularly in the arid and semiarid Loess Plateau. Based on field observations from 2001 to 2020, we methodically characterized the spatial–temporal dynamics of SIC and driving factors in a forage-crop rotation system. The results showed that 19 years continuous application of no-till or stubble retention practices resulted in SIC loss at the 0–10 cm soil depth at rates of 0.01–0.07 g kg−1 yr−1, the introduction of leguminous forages reduced the loss rate. The effects on SIC were greater at the 60–500 cm soil depth than at the 0–60 cm soil depth, SIC accumulated significantly in the deeper layer, and leaching and re-precipitation mainly occurred in the 60–200 cm layer. When performed on average over the 0–500 cm soil profile, no-till and stubble retention increased the SIC storage by 1.87–4.78 t ha−1 after maize harvest, while reduced by 1.04–1.20 t ha−1 after vetch harvest. The effects on SIC were mainly influenced by soil organic carbon according to the structural equation model. We concluded that leguminous forage introduction and returning to the field reduced the SIC loss in the rotation systems. The results highlight the importance of better understanding SIC dynamics when predicting the soil carbon budget.

Vegetation redistribution is predicted to intensify soil organic carbon loss under future climate changes on the Tibetan Plateau

Vegetation redistribution may bring unexpected climate-soil carbon cycling in terrestrial biomes. However, whether and how vegetation redistribution alters the soil carbon pool under climate change is still poorly understood on the Tibetan Plateau. Here, we applied the G-Range model to simulate the cover of herbs, shrubs and trees, net primary productivity (NPP) and soil organic carbon density (SOCD) at the depth of 60 cm on Tibetan Plateau for the individual years 2020 and 2060, using climate projection for Representative Concentration Pathways (RCP) 4.5 and RCP8.5 scenarios with the RegCM4.6 model system. Vegetation redistribution was defined as the transitions in bare ground, herbs, shrubs and trees between 2020 and 2060, with approximately 57.9 % (RCP4.5) and 59 % (RCP8.5) of the area will redistribute vegetation over the whole Tibetan Plateau. The vegetation cover will increase by about 2.4 % (RCP4.5) and 1.9 % (RCP8.5), while the NPP and SOCD will decrease by about −14.3 g C m−2 yr−1 and −907 g C m−2 (RCP4.5), and −1.8 g C m−2 yr−1and −920 g C m−2 (RCP8.5). Shrubs and trees will expand in the east, and herbs will expand in the northwest part of the Plateau. These areas are projected to be hotspots with greater SOCD reduction in response to future climate change, and will include lower net plant carbon input due to the negative NPP. Our study indicates that the SOC pool will become a carbon source under increased air temperature and rainfall on the Tibetan Plateau by 2060, especially for the area with vegetation redistribution. These results revealed the potential risk of vegetation redistribution under climate change in alpine ecosystems, indicating the policymakers need to pay attention on the vegetation redistribution to mitigate the soil carbon emission and achieve the goal of carbon neutrality on the Tibetan Plateau.

Degradation exposure scenario in the Brazilian Amazon: Edge effect on hyperdominant C-cycle tree species

The Amazon basin strongly influences the global carbon cycle, storing billions of tonnes of carbon in a relatively small number of ‘hyperdominant’ tree species. However, the Amazon carbon stock is threatened by land-use change. In the remaining forest patches, trees close to the forest border bear various physical and biotic edge effects that alter plant growth and survival. To assess how edge effects influence tree mortality and carbon storage, we investigated the occurrence of hyperdominant tree species in the Brazilian Amazon between 1988 and 2021. Evaluating tree records from a network of permanent plots and herbarium collections, we found that 22 % of tree occurrence records were in deforested areas, 35% within 1 km of the forest edge, and 43 % in continuous forest. At the local scale in Central Amazonia, tree monitoring data over 30 years revealed that forest fragments hyperdominant trees had twice the mortality rate of continuous forest ones due to edge effects during the 15 years following edge establishment. Although trees in fragments had higher initial growth, this pattern declined over the years and eventually resulted in significant carbon loss, mainly from tree mortality. Edge effects have led to annual declines in the biomass of forest remnants, suggesting that hyperdominant species are also susceptible to disturbances that lead to degradation and forest losses. Conservation of the Amazon forests requires an approach that considers the effects of local disturbances on carbon stocks in the region.

Microbiota recovery in a chronosquences of impoverished Cerrado soils with biosolids applications

Mining activities put the Brazilian savannas, a global biodiversity hotspot, in danger of species and soil carbon losses. Experiments employing biosolids have been applied to rejuvenate this degraded ecosystem, but a lingering question yet to be answered is whether the microbiota that inhabits these impoverished soils can be recovered towards its initial steady state after vegetation recovery. Here, we selected an 18-year-old restoration chronosequence of biosolids-treated, untreated mining and native soils to investigate the soil microbiota recovery based on composition, phylogeny, and diversity, as well as the potential factors responsible for ecosystem recovery. Our results revealed that the soil microbiota holds a considerable recovery potential in the degraded Cerrado biome. Biosolids application not only improved soil health, but also led to 41.7 % recovery of the whole microbial community, featuring significantly higher microbiota diversity and enriched groups (e.g., Firmicutes) that benefit carbon storage compared to untreated mining and native soils. The recovered community showed significant compositional distinctions from the untreated mining or native soils, rather than phylogenetic differences, with physiochemical properties explaining 55 % of the overall community changes. This study advances our understanding of soil microbiota dynamics in response to disturbance and restoration by shedding light on its recovery associated with biosolid application in a degraded biodiverse ecosystem.

Active afforestation of drained peatlands is not a viable option under the EU Nature Restoration Law

The EU Nature Restoration Law (NRL) is critical for the restoration of degraded ecosystems and active afforestation of degraded peatlands has been suggested as a restoration measure under the NRL. Here, we discuss the current state of scientific evidence on the climate mitigation effects of peatlands under forestry. Afforestation of drained peatlands without restoring their hydrology does not fully restore ecosystem functions. Evidence on long-term climate benefits is lacking and it is unclear whether CO2 sequestration of forest on drained peatland can offset the carbon loss from the peat over the long-term. While afforestation may offer short-term gains in certain cases, it compromises the sustainability of peatland carbon storage. Thus, active afforestation of drained peatlands is not a viable option for climate mitigation under the EU Nature Restoration Law and might even impede future rewetting/restoration efforts. Instead, restoring hydrological conditions through rewetting is crucial for effective peatland restoration.

Soil health—From practical issues to indicators: A workshop at the 1st European Healthy Soils Conference

AbstractThe aim of the 1st European Healthy Soils Conference in September 2023 in Muttenz, Switzerland, was to bring together professionals working on soil health from academia, the private sector, policymakers and students. Within the conference, a workshop ‘From Practical Issues to Indicators’ was held. In addition to flash presentations and subsequent discussion rounds, the opinions of the participants on the definition of soil health and the major soil threats were also collected. A majority of participants were in favour of the statement: ‘Healthy soils are in good chemical, biological and physical condition so that they can provide ecosystem services that are vital to humans and environment’. Of the 10 soil threats put forward for discussion, the participants voted for the four most important at European level, those being soil erosion, loss of soil organic carbon, loss of soil biodiversity and soil compaction. The need for long‐term observation plots in different agro‐ecosystems in Europe was emphasised in contributions to the discussion. Furthermore, methodological developments and standardisations that are simple and direct enough to be accepted and applied at the practical level by farmers and advisors were called for.

Carbon border adjustment mechanism challenges and implications: The case of Visegrád countries

Stricter climate policies across the European Union are enhancing the phenomenon of free riding by nonacting countries, which translates into carbon leakage and loss of competitiveness. This paper investigates the trade, economic and environmental implications of the future implementation of a carbon border adjustment mechanism (CBAM) in Visegrád countries as EU member states. We exploit trade data to estimate price and income elasticities for emission-intensive trade-exposed (EITE) goods imported from non-EU trading partners to Visegrád countries. Based on these estimates, which are combined with the average carbon intensity of the EU's proposed list of EITE goods, we simulate the implications of six different configurations of restrictiveness of the CBAM imposed on imports from non-EU countries. We find that a high price elasticity and carbon intensity tend to significantly decrease import demand for EITE goods under the CBAM. Moreover, future CBAM implementation will yield a relatively small adverse impact on economic growth in Visegrád countries and a small decrease in total carbon emissions in non-EU countries.

Qualitative evaluation of nine agricultural methods for increasing soil carbon storage in Norway

AbstractCarbon content is a key property of soils with importance for all ecosystem functions. Measures to increase soil carbon storage are suggested with the aim to compensate for agricultural emissions. In Norway, where soils have relatively high carbon content because of the cold climate, adapting management practices that prevent the loss of carbon to the atmosphere in response to climate change is also important. This work presents an overview of the potential for carbon sequestration in Norway from a wide range of agricultural management practices and provides recommendations based on certainty in the reported potential, availability of the technology, and likelihood for implementation by farmers. In light of the high priority assigned to increased food production and degree of self‐sufficiency in Norway, the following measures were considered: (1) utilization of organic resources, (2) use of biochar, (3) crop diversification and the use of cover crops, (4) use of plants with larger and deeper root systems, (5) improved management of meadows, (6) adaptive grazing of productive grasslands (7) managing grazing in extensive grasslands, (8) altered tillage practices, and (9) inversion of cultivated peat with mineral soil. From the options assessed, the use of cover crops scored well on all criteria evaluated, with a higher sequestration potential than previously estimated (0.2 Mt CO2‐equivalents annually). Biochar has the largest potential in Norway (0.9 Mt CO2‐equivalents annually, corresponding to 20% of Norwegian agricultural emissions and 2% of total national emissions), but its readiness level is not yet achieved despite interest from industry to apply this technology at large scale. Extensive grazing and the use of deep‐rooted plants also have the potential for increasing carbon storage, but there is uncertainty regarding their implementation and the quantification of effects from adapting these measures. Based on the complexities of implementation and the expected impacts within a Norwegian context, promising options with substantial payoff are few. This work sheds light on the knowledge gaps remaining before the presented measures can be implemented.

Process and quality evaluation of different improved composts made with a smart laboratory pilot plant

This study monitored the process and investigated the quality of compost obtained from different biomasses. Five blends of agri-food waste were composted by a laboratory pilot plant named COMPOSTER, that is designed to optimize biodegradation, and produce compost efficiently. The COMPOSTER consists of two 35-liter nearly adiabatic, aerated bioreactors that simulate an industrial process involving the typical sequence of mesophilic-thermophilic-mesophilic phases. It continuously monitors and records temperature, internal pressure, and biomass weight, while controlling and quantifying oxygen consumption and carbon dioxide emissions resulting from aerobic biodegradation. All composts were characterized for their main chemical, physical, and molecular features, as well as their suppressiveness against Fusarium oxysporum f.sp. lycopersici (FOL), tested on tomato seedlings. Optimized biodegradation yielded 50–60 % mature compost with a cumulative oxygen consumption ranging from 282 to 456 gO2 per kg of dry matter, with peaks of 2.55 gO2 per kg of volatile solids per hour, and carbon dioxide emissions of 22–36 % of the initial carbon content, with peaks of 5.89 g CO2 per kg of volatile solids per hour. Blends containing more ligno-cellulosic ingredients showed higher yields and lower CO2 emissions. Most of the nitrogen present initially was retained in the final compost; indeed, all mixtures exhibited an apparent nitrogen concentration increase due to carbon loss. Composting determined deep modifications in the molecular structure of the organic matter. 13C CPMAS-NMR and off-line thermochemolysis GC-MS analyses highlighted decomposition degree of polysaccharides and peptidic moieties, selective preservation of aliphatic and aromatic recalcitrant compounds, and optimal ongoing humification. All composts were non-phytotoxic, except for that including pepper crop residues, and all resulted rich in macro- and micro-elements for plant nutrition and proved to be active in controlling FOL disease. Compost comprising 81.2 % tomato crop waste exhibited the best growth performance and pathogen control on tomato. Mature, non-phytotoxic, nutrient-rich, and suppressive composts represent promising by-products that can be successfully recycled in agriculture, including high-value applications, leading to lower use of fertilizers and pesticides.

Reading tea leaves worldwide: Decoupled drivers of initial litter decomposition mass-loss rate and stabilization.

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models.

Prediction of soil organic carbon stock combining Sentinel-1 and Sentinel-2 images in the Zoige Plateau, the northeastern Qinghai-Tibet Plateau

Abstract Background Soil organic carbon (SOC) is a critical component of the global carbon cycle, and an accurate estimate of regional SOC stock (SOCS) would significantly improve our understanding of SOC sequestration and cycles. Zoige Plateau, locating in the northeastern Qinghai-Tibet Plateau, has the largest alpine marsh wetland worldwide and exhibits a high sensitivity to climate fluctuations. Despite an increasing use of optical remote sensing in predicting regional SOCS, optical remote sensing has obvious limitations in the Zoige Plateau due to highly cloudy weather, and knowledge of on the spatial patterns of SOCS is limited. Therefore, in the current study, the spatial distributions of SOCS within 100 cm were predicted using an XGBoost model—a machine learning approach, by integrating Sentinel-1, Sentinel-2 and field observations in the Zoige Plateau. Results The results showed that SOC content exhibited vertical distribution patterns within 100 cm, with the highest SOC content in topsoil. The tenfold cross-validation approach showed that XGBoost model satisfactorily predicted the spatial patterns of SOCS with a model efficiency of 0.59 and a root mean standard error of 95.2 Mg ha−1. Predicted SOCS showed a distinct spatial heterogeneity in the Zoige Plateau, with an average of 355.7 ± 123.1 Mg ha−1 within 100 cm and totaled 0.27 × 109 Mg carbon. Conclusions High SOC content in topsoil highlights the high risks of significant carbon loss from topsoil due to human activities in the Zoige Plateau. Combining Sentinel-1 and Sentinel-2 satisfactorily predicted SOCS using the XGBoost model, which demonstrates the importance of selecting modeling approaches and satellite images to improve efficiency in predicting SOCS distribution at a fine spatial resolution of 10 m. Furthermore, the study emphasizes the potential of radar (Sentinel-1) in developing SOCS mapping, with the newly developed fine-resolution mapping having important applications in land management, ecological restoration, and protection efforts in the Zoige Plateau.

Global synthesis on the response of soil microbial necromass carbon to climate-smart agriculture.

Climate-smart agriculture (CSA) supports the sustainability of crop production and food security, and benefiting soil carbon storage. Despite the critical importance of microorganisms in the carbon cycle, systematic investigations on the influence of CSA on soil microbial necromass carbon and its driving factors are still limited. We evaluated 472 observations from 73 peer-reviewed articles to show that, compared to conventional practice, CSA generally increased soil microbial necromass carbon concentrations by 18.24%. These benefits to soil microbial necromass carbon, as assessed by amino sugar biomarkers, are complex and influenced by a variety of soil, climatic, spatial, and biological factors. Changes in living microbial biomass are the most significant predictor of total, fungal, and bacterial necromass carbon affected by CSA; in 61.9%-67.3% of paired observations, the CSA measures simultaneously increased living microbial biomass and microbial necromass carbon. Land restoration and nutrient management therein largely promoted microbial necromass carbon storage, while cover crop has a minor effect. Additionally, the effects were directly influenced by elevation and mean annual temperature, and indirectly by soil texture and initial organic carbon content. In the optimal scenario, the potential global carbon accrual rate of CSA through microbial necromass is approximately 980 Mt C year-1, assuming organic amendment is included following conservation tillage and appropriate land restoration. In conclusion, our study suggests that increasing soil microbial necromass carbon through CSA provides a vital way of mitigating carbon loss. This emphasizes the invisible yet significant influence of soil microbial anabolic activity on global carbon dynamics.

Satellite-detected large CO2 release in southwestern North America during the 2020–2021 drought and associated wildfires

Southwestern North America (SWNA) continuously experienced megadroughts and large wildfires in 2020 and 2021. Here, we quantified their impact on the terrestrial carbon budget using net biome production (NBP) estimates from an ensemble of atmospheric inversions assimilating in-situ CO2 and Carbon Observatory–2 (OCO-2) satellite XCO2 retrievals (OCO-2 v10 MIP Extension), two satellite-based gross primary production (GPP) datasets, and two fire CO2 emission datasets. We found that the 2020–2021 drought and associated wildfires in SWNA led to a large CO2 loss, an ensemble mean of 95.07 TgC estimated by the satellite inversions using both nadir and glint XCO2 retrievals (LNLG) within the OCO-2 v10 MIP, greater than 80% of SWNA’s annual total carbon sink. Moreover, the carbon loss in 2020 was mainly contributed by fire emissions while in 2021 mainly contributed by drought impacts on terrestrial carbon uptake. In addition, the satellite inversions indicated the huge carbon loss was mainly contributed by fire emissions from forests and grasslands along with carbon uptake reductions due to drought impacts on grasslands and shrublands. This study provides a process understanding of how some droughts and following wildfires affect the terrestrial carbon budget on a regional scale.

Environmental and genetic influence on the rate and spectrum of spontaneous mutations in Escherichia coli.

Spontaneous mutations are the ultimate source of novel genetic variation on which evolution operates. Although mutation rate is often discussed as a single parameter in evolution, it comprises multiple distinct types of changes at the level of DNA. Moreover, the rates of these distinct changes can be independently influenced by genomic background and environmental conditions. Using fluctuation tests, we characterized the spectrum of spontaneous mutations in Escherichia coli grown in low and high glucose environments. These conditions are known to affect the rate of spontaneous mutation in wild-type MG1655, but not in a ΔluxS deletant strain - a gene with roles in both quorum sensing and the recycling of methylation products used in E. coli's DNA repair process. We find an increase in AT>GC transitions in the low glucose environment, suggesting that processes relating to the production or repair of this mutation could drive the response of overall mutation rate to glucose concentration. Interestingly, this increase in AT>GC transitions is maintained by the glucose non-responsive ΔluxS deletant. Instead, an elevated rate of GC>TA transversions, more common in a high glucose environment, leads to a net non-responsiveness of overall mutation rate for this strain. Our results show how relatively subtle changes, such as the concentration of a carbon substrate or loss of a regulatory gene, can substantially influence the amount and nature of genetic variation available to selection.