Atmospheric CO2 Concentration Research Articles

On the Large Variation in Atmospheric CO2 Concentration at Shangdianzi GAW Station during Two Dust Storm Events in March 2021

Dust storms have large impacts on air quality and meteorological elements; however, their relationships with atmospheric greenhouse gases (e.g., CO2) and radiation components remain uncertain. In this study, the co-variation of dust and CO2 concentrations and its possible influencing mechanism are examined using observations at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station along with simulations of the Vegetation Photosynthesis and Respiration Model coupled with the Weather Research and Forecasting model (WRF-VPRM), during two dust storm events on 15 and 28 March 2021. During these events, hourly CO2 concentrations decreased by 40–50 ppm at SDZ while dust concentrations increased to 1240.6 and 712.4 µg m−3. The elevated dust increased diffusive shortwave irradiance by 50–60% and decreased direct shortwave irradiance by ~60% along with clouds. The dust events were attributed to the passages of two cold front systems over northern China. At SDZ, during the frontal passages, wind speed increased by 3–6 m s−1, and relative humidity decreased by 50–60%. The CO2 variations associated with the frontal systems were captured by the WRF-VPRM despite the overestimated surface CO2 level at SDZ. Biogenic CO2 flux plays an indistinctive role in the large CO2 variation at SDZ, as it is weak during the non-growing season. The cold fronts pushed polluted air southeastward over the North China Plain and replaced it with low-CO2 air from Northwest China, leading to the decline in CO2. These findings demonstrate that mesoscale synoptic conditions significantly affect the regional transport and dispersion of CO2, which can influence the prediction of terrestrial carbon balance on a regional scale.

Relationship between CO2 Fertilization Effects, and Stand Age, Stand Type, and Site Conditions

The CO2 fertilization effect (CFE) plays a crucial role in the amelioration of climate change. Many physiological and environmental factors, such as stand age, stand type, and site conditions, may affect the extent of the CFE. However, the relationship between the CFE and these factors remains elusive. In this study, we used the emerging gross primary production (GPP) remote sensing products, with GPP predicted using eddy covariance–light use efficiency models (EC-LUE GPP) based on satellite near-infrared reflectance of vegetation (NIRv GPP) and assessed with a random forest model to explore the CFE trends with stand age in a coniferous forest and a broad-leaved forest in Heilongjiang Province, China. We additionally compared the differences among the CFEs under different site conditions. The CFEs in coniferous forests and broad-leaved forests both showed a rapid increase in stands of 10 to 20 years of age, followed by a decline after reaching a maximum, with the rate of decline reducing with age. Eventually, CFE remained stable in stands near 100 years of age. However, the CFE in coniferous forests exhibited more extended periods of rapid increase and a higher maximum than in broad-leaved forests. Moreover, in this study, we used the site class index (SCI) to grade site conditions. The results demonstrate that the CFE differed significantly under different levels of site conditions, and these differences gradually decreased with age. The site with the highest SCI had fewer environmental restrictions on the CFE, and consequently, the CFE rate of decline was faster. Our results are of significance in understanding the CFE and adapting to future changes in atmospheric CO2 concentration.

Higher site productivity and stand age enhance forest susceptibility to drought-induced mortality

Warmer and drier conditions increase forest mortality worldwide. At the same time, nitrogen deposition, longer growing seasons and higher atmospheric CO2 concentrations may increase site productivity accelerating forest growth. However, tree physiological studies suggest that increased site productivity can also have adverse effects, reducing adaptation to drought. Understanding such intricate interactions that might foster tree mortality is essential for designing activities and policies aimed at preserving forests and the ecosystem services they provide. This study shows how site factors and stand features affect the susceptibility of Scots pine to drought-induced stand-level mortality. We use extensive forest data covering 750,000 ha, including 47,450 managed Scots pine stands, of which 2,547 were affected by mortality during the drought in 2015–2019. We found that the oldest and most dense stands growing on the most productive sites showed the highest susceptibility to enhanced mortality during drought. Our findings suggest that increasing site productivity may accelerate the intensity and prevalence of drought-induced forest mortality. Therefore, climate change may increase mortality, particularly in old and high-productive forests. Such exacerbated susceptibility to mortality should be considered in forest carbon sink projections, forest management, and policies designed to increase resilience and protect forest ecosystems.

Higher vegetation sensitivity to meteorological drought in autumn than spring across European biomes

Europe has experienced severe drought events in recent decades, posing challenges to understand vegetation responses due to diverse vegetation distribution, varying growth stages, different drought characteristics, and concurrent hydroclimatic factors. To analyze vegetation response to meteorological drought, we employed multiple vegetation indicators across European biomes. Our findings reveal that vegetation sensitivity to drought increases as the canopy develops throughout the year, with sensitivities from −0.01 in spring to 0.28 in autumn and drought-susceptible areas from 18.5 to 57.8% in Europe. Soil water shortage exacerbates vegetation-drought sensitivity temporally, while its spatial impact is limited. Vegetation-drought sensitivity strongly correlates with vapor pressure deficit and partially with atmospheric CO2 concentration. These results highlight the spatiotemporal variations in vegetation-drought sensitivities and the influence of hydroclimatic factors. The findings enhance our understanding of vegetation response to drought and the impact of concurrent hydroclimatic factors, providing valuable sub-seasonal information for water management and drought preparedness.

Effects of paleogeographic changes and CO2 variability on northern mid-latitudinal temperature gradients in the Cretaceous

The Cretaceous ‘greenhouse’ period (~145 to ~66 million years ago, Ma) in Earth’s history is relatively well documented by multiple paleoproxy records, which indicate that the meridional sea surface temperature (SST) gradient increased (non-monotonically) from the Valanginian (~135 Ma) to the Maastrichtian (~68 Ma). Changes in atmospheric CO2 concentration, solar constant, and paleogeography are the primary drivers of variations in the spatiotemporal distribution of SST. However, the particular contribution of each of these drivers (and their underlying mechanisms) to changes in the SST distribution remains poorly understood. Here we use data from a suite of paleoclimate simulations to compare the relative effects of atmospheric CO2 variability and paleogeographic changes on mid-latitudinal SST gradient through the Cretaceous. Further, we use a fundamental model of wind-driven ocean gyres to quantify how changes in the Northern Hemisphere paleogeography weaken the circulation in subtropical ocean gyres, leading to an increase in extratropical SSTs.

Review: The Energy Implications of Averting Climate Change Catastrophe

Conventional methods of climate change (CC) mitigation have not ‘bent the curve’ of steadily rising annual anthropic CO2 emissions or atmospheric concentrations of greenhouse gases. This study reviews the present position and likely future of such methods, using the recently published literature with a global context. It particularly looks at how fast they could be implemented, given the limited time available for avoiding catastrophic CC (CCC). This study then critically examines solar geoengineering, an approach often viewed as complementary to conventional mitigation. Next, this review introduces equity considerations and shows how these even further shorten the available time for effective action for CC mitigation. The main findings are as follows. Conventional mitigation approaches would be implemented too slowly to be of much help in avoiding CCC, partly because some suggested technologies are infeasible, while others are either of limited technical potential or, like wind and solar energy, cannot be introduced fast enough. Due to these problems, solar geoengineering is increasingly advocated for as a quick-acting and effective solution. However, it could have serious side effects, and, given that there would be winners and losers at the international level as well as at the more regional level, political opposition may make it very difficult to implement. The conclusion is that global energy consumption itself must be rapidly reduced to avoid catastrophic climate change, which requires strong policy support.

Review of carbon dioxide mineralization of magnesium‐containing materials

AbstractThe increasing utilization of fossil fuels and industrial activities has resulted in a surge of CO2 emissions, which have significantly impacted global climate change. Carbon capture and utilization technologies offer a promising solution to decrease atmospheric CO2 concentrations and convert CO2 into valuable products. This study focuses on the capture and storage of CO2 through the mineralization of magnesium‐containing materials. The analysis encompasses the mineralization process of solid and liquid minerals, the various mineralization processes of magnesium‐containing minerals categorized as direct and indirect mineralization, and the latest research advancements in magnesium‐containing minerals. Brine and seawater from salt lakes are considered the most appropriate materials for mineralization due to their abundance and the simplicity of the process compared to solid mineralization. This paper analyzes the impact of temperature, impurity ions, additives, and microorganisms on the process of magnesium carbonate synthesis crystallization. The use of magnesium‐containing materials for carbon dioxide sequestration can effectively reduce carbon emission. The review offers guidance on carbon dioxide mineralization and explores the potential applications of magnesium mineralization.

Gross primary productivity and the predictability of CO2: more uncertainty in what we predict than how well we predict it

Abstract. The prediction of atmospheric CO2 concentrations is limited by the high interannual variability (IAV) in terrestrial gross primary productivity (GPP). However, there are large uncertainties in the drivers of GPP IAV among Earth system models (ESMs). Here, we evaluate the impact of these uncertainties on the predictability of atmospheric CO2 in six ESMs. We use regression analysis to determine the role of environmental drivers in (i) the patterns of GPP IAV and (ii) the predictability of GPP. There are large uncertainties in the spatial distribution of GPP IAV. Although all ESMs agree on the high IAV in the tropics, several ESMs have unique hotspots of GPP IAV. The main driver of GPP IAV is temperature in the ESMs using the Community Land Model, whereas it is soil moisture in the ESM developed by the Institute Pierre Simon Laplace (IPSL-CM6A-LR) and in the low-resolution configuration of the Max Planck Earth System Model (MPI-ESM-LR), revealing underlying differences in the source of GPP IAV among ESMs. Between 13 % and 24 % of the GPP IAV is predictable 1 year ahead, with four out of six ESMs showing values of between 19 % and 24 %. Up to 32 % of the GPP IAV induced by soil moisture is predictable, whereas only 7 % to 13 % of the GPP IAV induced by radiation is predictable. The results show that, while ESMs are fairly similar in their ability to predict their own carbon flux variability, these predicted contributions to the atmospheric CO2 variability originate from different regions and are caused by different drivers. A higher coherence in atmospheric CO2 predictability could be achieved by reducing uncertainties in the GPP sensitivity to soil moisture and by accurate observational products for GPP IAV.

From Stress to Success: Harnessing Technological Advancements to Overcome Climate Change Impacts in Citriculture

Climate change, primarily caused by human activities, leads to persistent alterations in Earth’s long-term weather patterns and temperatures, resulting in substantial regional climate disparities that significantly impact agricultural output. In the realm of sustainable citriculture, climate change poses a notable challenge by inducing abiotic stresses within citrus-producing regions. Projections suggest rising air temperatures by 2.2-5.1 °C, heightened instances of temperatures exceeding 30 °C during dry spells, freezing events, a reduction in rainfall by at least 4%, and amplified monsoonal precipitations. Such changes will inevitably affect citrus tree physiology and yield quality. The intricate connection between external climatic conditions and crucial physiological processes underscores the profound influence of climate change. Temperature fluctuations can disrupt leaf photosynthesis, stomatal conductance, flower and fruit development, fruit sugar production, coloration, abscission, carbohydrate accumulation, and ultimate fruit yield. This comprehensive review delves into the specific repercussions of climate change on citrus cultivation, focusing on variables like temperature variations, water availability, light intensity, atmospheric CO2 concentration, and salinity stress. Our exploration elucidates the adverse impact of these stressors on citrus crops, while highlighting innovative tactics and emerging technologies, including advanced monitoring systems, precision irrigation, automated climate regulation, molecular priming through biostimulants, shade netting, and particle film technologies. By mitigating the adverse effects of environmental stressors, these strategies empower citrus growers to navigate challenges like excessive solar radiation, temperature fluctuations, soil moisture management, erosion prevention, and enhanced soil quality. These combined efforts forge a path toward a more resilient citriculture capable of effectively countering the abiotic stresses stemming from climate change.

Colonial morphology weakens the response of different inorganic carbon uptake systems to CO2 levels in Microcystis population

Rising atmospheric CO2 concentration negatively impacts aquatic ecosystems and may induce evolutionary changes in the CO2-concentrating mechanism (CCM) of cyanobacteria. As the most notorious freshwater cyanobacteria, Microcystis strains have high phenotypic plasticity to form colonies and blooms in lakes and reservoirs worldwide. However, phenotypic plasticity of Microcystis responses to elevated CO2 is still a major open question. Here, we studied how Microcystis strains with two genotype of inorganic carbon uptake systems, bicA and sbtA, and different colonial morphology response to 200 ppm, 400 ppm, and 800 ppm CO2 levels. The results revealed that sbtA genotypes showed significantly higher specific growth rates, Chl a concentration, and photosynthetic efficiency at 200 ppm CO2, whereas higher specific growth rates, Chl a concentration, and photosynthetic efficiency were found in bicA genotype at 800 ppm CO2. The highest values of specific growth rates, Chl a concentration, Fv/Fm, and maximal net photosynthesis (Pm) were observed in unicellular morphology, followed by small colony and large colonial morphology at all CO2 levels. The values of K0.5 (DIC), K0.5 (CO2), and K0.5 (HCO3−) in the large colonials increased with rising CO2 levels, but these values significantly decreased in the unicellular and small colonials. ANOSIM analysis indicated that colonial morphology reduced significantly inter-group differences between bicA and sbtA genotypes at all CO2 treatments. These results suggest that colonial morphology of Microcystis can weakens the response of different inorganic carbon uptake systems to CO2 levels. Moreover, phenotypic and genotypic plasticity is likely to broaden strongly the fitness of Microcystis from rising atmospheric CO2.

Surprising stability of recent global carbon cycling enables improved fossil fuel emission verification

AbstractThe interannual to decadal variability in natural carbon sinks limits the explanation of recent changes in atmospheric CO2 concentration. Here we account for interannual and decadal variability using a simple quasi-mechanistic model of the net land carbon exchange with terms scaling with atmospheric CO2 and a weighted spatial average of temperature anomalies. This approach reduces the unexplained residual in Earth’s carbon cycle budget from ±0.76 GtC per year obtained using process models to ±0.50 GtC per year, with the largest improvements on decadal timescales despite assuming constant dynamics. Our findings reveal remarkable stability of the carbon cycle and allow verification of reported global emissions to within 4.4% (95% confidence level) over the five-year stocktake cycle of the Paris Agreement—half the uncertainty reported previously.

Deterministic and stochastic components of atmospheric CO[formula omitted] inside forest canopies and consequences for predicting carbon and water exchange

Atmospheric CO2 concentrations strongly influence the exchange of energy, water and carbon between the atmosphere and the terrestrial biosphere. The CO2 available to plants can be highly variable given the stochastic nature of the phenomena involved in its dynamics. However, most terrestrial ecosystem models consider CO2 concentration as a quasi-deterministic variable or use measurements taken from heights above the canopy where CO2 is usually well mixed. Therefore, in this study, we aimed to evaluate if a stochastic treatment of CO2 concentrations leads to different predictions of carbon assimilation (An) and transpiration (T) compared to a strictly deterministic approach, as well as the use of CO2 measurements from different heights. To address this goal, we used a set of observations taken in forests from the ICOS network and the ATTO research site. We applied the exponential smoothing method to decompose the time series into their trend, seasonal and stochastic (residual) components. We found that the residual component of CO2 (rCO2) follows a Laplace probability density function and its stochastic magnitude is inversely proportional to the height above the ground. To quantify the degree to which predictions of An and T would be affected by stochastic effects, we ran simulations considering the different components of the time series and Farquhar’s and Penman–Monteith’s models. We found significant differences in the predictions of An and T for diverse heights, with larger An (T) fluxes closer (farther) to the ground. Still, this effect is mainly due to the deterministic component that increases with decreasing height. The stochastic component tends to reduce (increase) An (T) compared to the deterministic approach. However, the difference between approaches is not large enough to compensate for the deterministic effect, suggesting that there is no merit for the consideration of rCO2 in future simulations as long as measurements taken inside the canopy are used.

The Impact of Elevated Atmospheric Carbon Dioxide Exposure on Magic Tomatoes' Nutrition-Health Properties.

The release of carbon dioxide (CO2) into the atmosphere has accelerated during the last two decades. Elevated atmospheric CO2 concentration (eCO2) is known as an agent that improves plant photosynthesis. However, eCO2 was also correlated with alterations in the macronutrient and micronutrient compositions of various dietary crops. In order to explore the effect of eCO2 on the nutritional and health properties of tomatoes, three parental lines of the Magic population, which includes a large part of the genetic diversity present in large fruit varieties, were used as models. The plants were grown in growth chambers under ambient (400 ppm) or eCO2 (900 ppm) conditions. The macronutrient and micronutrient contents were measured. The anti-oxidant and anti-inflammatory bioactivities were assessed in vitro on activated macrophages. These analyses highlighted that the carbohydrate content was not affected by the eCO2, whereas the protein, carotenoid, lycopene, and mineral contents decreased. Regarding the anti-oxidant properties, no influence of eCO2 exposure was observed. Similarly, the anti-inflammatory properties were not affected by the eCO2. These data are in contrast with previous studies conducted on different plant species or accessions, indicating that the effect of eCO2 on crops' nutrition and health properties is based on complex mechanisms in which growth conditions and genetic backgrounds play a central role.

The Impacts of Elevated CO2 Levels on Environmental Risk of Heavy Metal Pollution in Agricultural Soils: Applicable Remediation Approaches for Integrated Benefits

Heavy metal pollution in agricultural fields is a serious health concern because of the high bioavailability and persistent toxicity of heavy metals. Much progress has recently been made with respect to elucidating the impacts of climate change (e.g., elevated atmospheric CO2 concentrations) on the environmental behavior of heavy metal pollutants and the associated ecological and health risks. The microbiological responses to elevated CO2 levels are primarily mediated by the C balance in agricultural activities; however, the underlying mechanisms involved in plant–soil–microbe interactions under heavy metal stress are still unclear. Thus, in this study, the challenges and perspectives with regard to controlling heavy metal pollution and optimizing crop yields while reducing greenhouse emissions in agricultural ecosystems responsive to elevated CO2 levels are discussed. Considering the integrated benefits of intensive agriculture and food security under a future changing climate, the summarized findings provided in this study may help to develop applicable remediation approaches for sustainably managing heavy metal polluted soils.

Characterizing the regional XCO2 variability and its association with ENSO over India inferred from GOSAT and OCO-2 satellite observations

India is primarily concerned with comprehending regional carbon source-sink response in the context of changes in atmospheric CO2 concentrations or anthropogenic emissions. Recent advancements in high-resolution satellite's fine-scale XCO2 measurements provide an opportunity to understand unprecedented details of source-sink activity on a regional scale. In this study, we investigated the long-term variations of XCO2 concentration and growth rates as well as its covarying relationship with ENSO and regional climate parameters (temperature, precipitation, soil moisture, and NDVI) over India from 2010 to 2021 using GOSAT and OCO-2 retrievals. The results show since the launch of OCO-2 in 2014, the number of monthly high-quality XCO2 soundings over India has grown nearly 100-fold compared to GOSAT, launched in 2009. Also, the discrepancy in XCO2 increase of 2.54(2.43) ppm/yr was observed in GOSAT (OCO-2) retrieval during an overlapping measurement period (2015–2021). Additionally, wavelet analysis indicated that the OCO-2 retrieval is able to capture a better frequency of local-scale XCO2 variability compared to GOSAT, owing to its high-resolution cloud-free XCO2 soundings, providing more well-defined regional-scale source-sink features. Furthermore, dominant spatial pattern of XCO2 variability observed over south and southeast of India in both satellites, with XCO2 semi-annual and annual variability more distinctly present in OCO-2 compared to GOSAT. A cross-correlation analysis suggested GOSAT XCO2 growth rate positively correlates with ENSO in different homogeneous monsoon regions of India, with ENSO leading the GOSAT XCO2 growth rate in all homogeneous regions by 3–9 months. The South Peninsular region sensitive to ENSO changes, especially during 2015–2016 ENSO event, where a decrease in CO2 uptake was observed is closely linked with precipitation, soil moisture, and temperature anomalies. However, regional climate parameters show a low correlation with XCO2 growth since CO2 is a long-lived well-mixed gas primarily having an imprint of large-scale transport in column CO2.

Smart Approaches for Evaluating Photosynthetically Active Radiation at Various Stations Based on MSG Prime Satellite Imagery

Photosynthetically active radiation (PAR) is the 400–700 nm portion of the solar radiation spectrum that photoautotrophic organisms including plants, algae, and cyanobacteria use for photosynthesis. PAR is a key variable in global ecosystem and Earth system modeling, playing a prominent role in carbon and water cycling. Alongside air temperature, water availability, and atmospheric CO2 concentration, PAR controls photosynthesis and consequently biomass productivity in general. The management of agricultural and horticultural crops, forests, grasslands, and even grasses at sports venues is a non-exhaustive list of applications for which an accurate knowledge of the PAR resource is desirable. Modern agrivoltaic systems also require a good knowledge of PAR in conjunction with the variables needed to monitor the co-located photovoltaic system. In situ quality-controlled PAR sensors provide high-quality information for specific locations. However, due to associated installation and maintenance costs, such high-quality data are relatively scarce and generally extend over a restricted and sometimes non-continuous period. Numerous studies have already demonstrated the potential offered by surface radiation estimates based on satellite information as reliable alternatives to in situ measurements. The accuracy of these estimations is site-dependent and is related, for example, to the local climate, landscape, and viewing angle of the satellite. To assess the accuracy of PAR satellite models, we inter-compared 11 methods for estimating 30 min surface PAR based on satellite-derived estimations at 33 ground-based station locations over several climate regions in Europe, Africa, and South America. Averaged across stations, the results showed average relative biases (relative to the measurement mean) across methods of 1 to 20%, an average relative standard deviation of 25 to 30%, an average relative root mean square error of 25% to 35% and a correlation coefficient always above 0.95 for all methods. Improved performance was seen for all methods at relatively cloud-free sites, and quality degraded towards the edge of the Meteosat Second Generation viewing area. A good compromise between computational time, memory allocation, and performance was achieved for most locations using the Jacovides coefficient applied to the global horizontal irradiance from HelioClim-3 or the CAMS Radiation Service. In conclusion, satellite estimations can provide a reliable alternative estimation of ground-based PAR for most applications.

Effects of elevated CO2 concentration and experimental warming on morphological, physiological, and biochemical responses of winter wheat under soil water deficiency.

Global climate change and freshwater scarcity have become two major environmental issues that constrain the sustainable development of the world economy. Climate warming caused by increasing atmospheric CO2 concentration can change global/regional rainfall patterns, leading to uneven global seasonal precipitation distribution and frequent regional extreme drought events, resulting in a drastic reduction of available water resources during the critical crop reproduction period, thus causing many important food-producing regions to face severe water deficiency problems. Understanding the potential processes and mechanisms of crops in response to elevated CO2 concentration and temperature under soil water deficiency may further shed lights on the potential risks of climate change on the primary productivity and grain yield of agriculture. We examined the effects of elevated CO2 concentration (e[CO2]) and temperature (experimental warming) on plant biomass and leaf area, stomatal morphology and distribution, leaf gas exchange and mesophyll anatomy, rubisco activity and gene expression level of winter wheat grown at soil water deficiency with environmental growth chambers. We found that e[CO2] × water × warming sharply reduced plant biomass by 57% and leaf photosynthesis (P n) 50%, although elevated [CO2] could alleviated the stress from water × warming at the amount of gene expression in RbcL3 (128%) and RbcS2 (215%). At ambient [CO2], the combined stress of warming and water deficiency resulted in a significant decrease in biomass (52%), leaf area (50%), P n (71%), and G s (90%) of winter wheat. Furthermore, the total nonstructural carbohydrates were accumulated 10% and 27% and increased R d by 127% and 99% when subjected to water × warming and e[CO2] × water × warming. These results suggest that water × warming may cause irreversible damage in winter wheat and thus the effect of "CO2 fertilization effect" may be overestimated by the current process-based ecological model.

Antagonistic or Compensatory: Crosstalk between ABA and Ethylene in Regulating Stomatal Behavior under High CO2 and Progressive Soil Drying.

Increasing atmospheric CO2 concentrations accompanied by intensified drought stress have a significant impact on plant growth and physiology. The aim of this study was to explore the role of abscisic acid (ABA) in mediating the response of stomata to elevated CO2 (e[CO2]) and soil water deficits. Tomato plants with different endogenous ABA concentrations (Ailsa Craig (AC), its ABA-deficient mutant (flacca) and ABA-overproduction transgenic tomato (SP5)) were grown in ambient (a[CO2], 400 μmol mol -1) and elevated (800 μmol mol -1) CO2 environments and were subjected to progressive soil drying at six-leaf stage. Results showed that, compared to plants grown under a[CO2], e[CO2]-plants had significantly lower stomatal conductance in AC and SP5 but not in flacca. Under drought, e[CO2]-plants had better water status and higher water use efficiency at both leaf and whole plant levels. e[CO2] had no effects on the ABA concentration of plants under well-watered conditions but promoted the accumulation of ABA in leaves of plants subjected to drought stress, which coincided with the upregulated expression of ABA biosynthetic genes and downregulated expression of ABA metabolic genes. Although in flacca, the increase of ABA induced by drought was much less than in AC and SP5, it accumulated large amounts of ethylene, suggesting that in plants with ABA deficiency, ethylene may play a compensatory role in inducing stomatal closure during soil drying. Collectively, these findings improve our understanding of plant performances to a future drier and CO2-enriched environment.

Superpixel-Based Style Transfer Method for Single-Temporal Remote Sensing Image Identification in Forest Type Groups

Forests are the most important carbon reservoirs on land, and forest carbon sinks can effectively reduce atmospheric CO2 concentrations and mitigate climate change. In recent years, various satellites have been launched that provide opportunities for identifying forest types with low cost and high time efficiency. Using multi-temporal remote sensing images and combining them with vegetation indices takes into account the vegetation growth pattern and substantially improves the identification accuracy, but it has high requirements for imaging, such as registration, multiple times, etc. Sometimes, it is difficult to satisfy, the plateau area is severely limited by the influence of clouds and rain, and Gaofen (GF) data require more control points for orthophoto correction. The study area was chosen to be Huize County, situated in Qujing City of Yunnan Province, China. The analysis was using the GF and Landsat images. According to deep learning and remote sensing image feature extraction methods, the semantic segmentation method of F-Pix2Pix was proposed, and the domain adaptation method according to transfer learning effectively solved the class imbalance in needleleaf/broadleaf forest identification. The results showed that (1) this method had the best performance and a higher accuracy than the existing products, 21.48% in non-forest/forest and 29.44% in needleleaf/broadleaf forest for MIoU improvement. (2) Applying transfer learning domain adaptation to semantic segmentation showed significant benefits, and this approach utilized satellite images of different resolutions to solve the class imbalance problem. (3) It can be used for long-term monitoring of multiple images and has strong generalization. The identification of needleleaf and broadleaf forests combined with the actual geographical characteristics of the forest provides a foundation for the accurate estimation of regional carbon sources/sinks.

Boreal conifers maintain carbon uptake with warming despite failure to track optimal temperatures

Warming shifts the thermal optimum of net photosynthesis (ToptA) to higher temperatures. However, our knowledge of this shift is mainly derived from seedlings grown in greenhouses under ambient atmospheric carbon dioxide (CO2) conditions. It is unclear whether shifts in ToptA of field-grown trees will keep pace with the temperatures predicted for the 21st century under elevated atmospheric CO2 concentrations. Here, using a whole-ecosystem warming controlled experiment under either ambient or elevated CO2 levels, we show that ToptA of mature boreal conifers increased with warming. However, shifts in ToptA did not keep pace with warming as ToptA only increased by 0.26–0.35 °C per 1 °C of warming. Net photosynthetic rates estimated at the mean growth temperature increased with warming in elevated CO2 spruce, while remaining constant in ambient CO2 spruce and in both ambient CO2 and elevated CO2 tamarack with warming. Although shifts in ToptA of these two species are insufficient to keep pace with warming, these boreal conifers can thermally acclimate photosynthesis to maintain carbon uptake in future air temperatures.