[Identification of Priority Areas for Carbon Compensation in Chongqing Based on the Difference in Land Use Carbon Budget].

This study aimed to explore the spatiotemporal patterns and balance characteristics of land use carbon budget, measure the value of carbon compensation, and delineate carbon compensation type zoning to provide scientific reference for further strengthening the connection between the construction of an ecological compensation system and the "dual carbon" target task. Based on the land cover data of Chongqing from 2000 to 2020, this study analyzed the spatiotemporal dynamics and balance relationship characteristics of the land use carbon budget. By using the revised carbon compensation model to measure the horizontal compensation standards, the normalized revealed comparative advantage （NRCA） index and K-means clustering analysis method were used to divide the carbon compensation area. The research results demonstrated that： ① the total land use carbon sequestration in Chongqing grew slowly from 2000 to 2020, whereas carbon emissions continued to increase significantly, and the net carbon emissions showed a distribution pattern of "high in the center and low in the two wings." ② The average coefficient of variation in Chongqing was 0.602, and the carbon emission economy contributive coefficient and carbon ecological support coefficient were concentrated between 0.64-1.14 and 0.00-32.86, respectively. The difference in the contribution of carbon emissions and economic benefits between districts and counties was relatively small, but there was a mismatch between carbon supply and demand. ③ A significant spatial difference existed in the value of carbon compensation, with a total of 1.098 billion yuan in carbon payment and 634 million yuan in carbon compensation, respectively. Moreover, it was ultimately determined that there were eight key payment areas, seven general payment areas, three key compensation areas, and 20 general compensation areas. In conclusion, the research results can provide a reference for implementing differentiated development strategies in different types of carbon compensation regions, improve the collaborative governance capacity of the regional ecological environment, and promote the achievement of carbon neutrality goals.

[Spatial Correlation of Land Use Carbon Budget Based on Social Network Analysis： A Case Study of Chongqing Metropolitan Area].

Clarifying the temporal and spatial changes in the carbon budget in the Chongqing metropolitan area and exploring the spatial correlation of land use carbon budget are of great significance for realizing the regional "double carbon" goal. Using 21 districts and counties in Chongqing metropolitan area as the research scale, the IPCC inventory method, carbon emission coefficient method, Gini coefficient, gravity model, and social network analysis were used to estimate the net carbon emissions from land use in Chongqing metropolitan area from 2000 to 2020, and the spatial correlation of the carbon budget was obtained. The results revealed that： ① In the past 20 years, the carbon budget of the Chongqing metropolitan area showed an overall upward trend, with an average annual growth rate of 2.83%, and the spatial distribution was "higher in the north and south, higher in the east and west, and lower in the middle." ② During the past 20 years, the spatial difference of net carbon emissions in the Chongqing metropolitan area became highly average, and the overall Gini coefficient decreased by 11.42%, whereas the intra-group difference was the largest in key development zones. ③ In the past 20 years, the overall structure of the spatial correlation network of land use carbon budget in the Chongqing metropolitan area has become stable and complex, and the network density and network correlation number have increased by 0.43 and 180, respectively, the network correlation degree has increased to 1, and the network health degree has improved. ④ In the individual network structure of land use carbon budget in the Chongqing metropolitan area, the degree centrality of each district and county has increased, and the increase in the central urban area was the most significant, with an increase of 81, whereas the decline in intermediate centrality and proximity centrality has promoted the regional coordinated development and integration process in the metropolitan area. ⑤ In the past 20 years, the density of net carbon emissions in the Chongqing metropolitan area has increased as a whole, with the density of the core area increasing by 0.35 and the density of the core-edge area increasing by 0.34. By exploring the change and spatial correlation of land use carbon budget in the Chongqing metropolitan area, this study clarified the spatial distribution difference of carbon budget and provided support for regional green development.

[Spatiotemporal Differentiation of Carbon Budget and Carbon Compensation Zoning Based on the Plan for Major Function-oriented Zones：A Case Study of Counties in the Yellow River Basin].

Exploring the spatiotemporal differentiation of the carbon budget and clarifying the zoning of carbon compensation based on the perspective of the main function-oriented zones is of great significance for promoting regional low-carbon development and achieving the "dual carbon" goal. This study was conducted using 550 counties in the Yellow River Basin as the basic unit, and based on the concentration index to examine the spatial distribution characteristics of carbon emissions and carbon absorptions in the main function-oriented zones of the Yellow River Basin, a four-dimensional benchmark framework for carbon compensation zoning was constructed by total scale, economic contribution, ecological carrying capacity, and land development intensity. The SOM-K-means algorithm was used to establish a differentiated carbon compensation zoning scheme. The results showed that： ① The carbon emissions and carbon absorptions and their growth trends of the main function-oriented zones in the Yellow River Basin were in line with the positioning of the main functional area, and the significant space-time distribution characteristics of the concentration level of carbon emissions and carbon absorptions were shown. ② Significant regional differences exist in the four attributes of total carbon emissions scale, economic contribution, ecological carrying capacity, and land development intensity. The overall scale of carbon emissions showed a growth trend, with obvious comparative advantages in the midstream and downstream. The overall comparative advantage of economic contribution increased first and then decreased, with the midstream and downstream being the attribute advantage areas of economic contribution. The overall ecological carrying capacity had been improved, and the upstream had obvious advantages in ecological carrying properties. The advantageous areas for land development were mainly concentrated in the midstream and downstream； in particular, the comparative advantage index in the midstream was showing a rapid upward trend. ③ Moreover, there were 287 compensated areas, 78 balanced areas, and 185 payment areas in the Yellow River Basin. Eleven types of carbon compensation zones were finally formed by combining the comparative advantage index of four types of attributes with the plan for main function-oriented zones, and corresponding low-carbon development strategies were proposed for each type of zone.

Excluding livestock access to farm dams reduces methane emissions and boosts water quality.

Farm dams, also known as 'agricultural ponds', are ubiquitous features of agricultural landscapes globally. Those accessed by livestock have high methane (CH4) emissions per unit area relative to other freshwater systems. Fencing dams and installing water troughs to prevent livestock from entering the dams are promising strategies to improve water quality and substantially reduce their carbon footprints. However, previous studies only measured the effects of fencing on methane diffusive emissions without considering ebullitive fluxes (i.e., methane bubbles), which is often the dominant emission pathway in smaller water bodies. Also, data is lacking on how the benefits of fencing farm dams vary across seasons. Using Australia as a test case, this study investigates the benefit of fencing off farm dams by monitoring total CH4 (diffusion + ebullition) and carbon dioxide (CO2) in summer and winter. Fenced dams had 72 % lower CH4 emissions in summer and 92 % lower in winter than unfenced dams. Similarly, CO2-equivalent (CO2 + CH4) fluxes were lower in fenced dams by 59 % in summer and 73 % in winter. Fenced dams had higher water quality, with 51 % less total dissolved nitrogen, 57 % less phosphorous, and 23-49 % more dissolved oxygen. Average daily air temperature was a key predictor of CH4 emissions from farm dams, underscoring the importance of considering temporal dynamics for estimating yearly farm dam emissions. We confirmed that excluding livestock from entering farm dams using fences significantly mitigates CH4 emissions and enhances water quality, and these benefits are maintained seasonally.

Reuse of straw in the form of hydrochar: Balancing the carbon budget and rice production under different irrigation management.

Hydrochar is proposed as a climate-friendly organic fertilizer, but its potential impact on greenhouse gas (GHG) emissions in paddy cultivation is not fully understood. This two-year study compared the impact of exogenous organic carbon (EOC) application (rice straw and hydrochar) on GHG emissions, the net ecosystem carbon budget (NECB), net global warming potential (net GWP), and GHG emission intensity (GHGI) in a rice pot experiment using either flooding irrigation (FI) or controlled irrigation (CI). Compared with FI, CI increased ecosystem respiration by 23 - 44 % and N2O emissions by 85 - 137 % but decreased CH4 emissions by 30 - 58 % (p < 0.05). Since CH4 contributed more to net GWP than N2O, CI reduced net GWP by 16 - 220 %. EOC amendment increased crop yield by 5 - 9 % (p < 0.05). Compared with CK, hydrochar application increased initial GHG emission, net GWP and GHGI in the first year, while in the second year, there was no significant difference in net GWP and GHGI between CI-hydrochar and CK. Compared with straw addition, hydrochar amendment reduced net GWP and GHGI by 20 - 66 % and 21 - 66 %; and exhibited a lower net CO2 emission when considering the energy input during the hydrochar production. These findings suggest that integrated CI-hydrochar practices would be a sustainable and eco-friendly way for organic waste management in rice production as it holds potential to enhance the NECB and SOC sequestration of rice production, while also offsetting the extra carbon emissions from organic inputs.

Spatiotemporal evolution of carbon budget and carbon compensation zoning of urban agglomerations in the Yellow River Basin.

As a crucial industrial, agricultural, and energy base in China, the urban agglomerations in the Yellow River Basin (YRB) have faced increasingly significant pressure for carbon emission reduction since the implementation of the "Dual Carbon" strategy. This study focuses on 615 counties within the major urban agglomerations in the YRB, analyzing the spatiotemporal evolution of carbon budget in land use from 2000 to 2020. Methods such as the normalized revealed comparative advantage (NRCA) index and SOM-K-means model are employed to explore the carbon compensation zoning of counties in the urban agglomerations in the YRB from the perspective of main functional zones. The results show that: (1) From 2000 to 2020, there was a significant and continuous widening gap between carbon emissions and carbon absorption in the study area. The total carbon emissions increased significantly from 3.64 × 108 to 13.56 × 108 t, showing a "north high, south low" spatial distribution pattern. Meanwhile, the carbon absorption remained stable at around 6.47 × 107 t, with a spatial distribution pattern roughly characterized by "higher in the west, lower in the east, and highest in the central part". The carbon budget of various types of functional zones generally aligns well with their strategic positioning. (2) There is a significant regional difference in net carbon emissions among urban agglomerations, with the greatest internal variation observed in the Guanzhong Plain Urban Agglomeration (Gw = 0.471) and the most notable differences between the Lanzhou-Xining Urban Agglomeration and others (Gb = 0.554). (3) The study area consists of 273 payment zones, 257 balanced zones, and 85 compensated zones. Combining with the reconstruction of main functional areas, seven types of carbon compensation zones are identified.

[Land Use Change Driving and Optimization of Carbon Budget in Hangzhou Metropolitan Area].

As climate change, such as global warming, has become a global environmental issue, clarifying the mechanism driving the carbon budget based on land use change has become an inevitable path to realize the "double carbon" goal. Based on the land use change characteristics in the Hangzhou Metropolitan Area from 1995 to 2020, this study employed the inventory accounting method, concentration index, and panel regression models to investigate the driving mechanisms of carbon budget dynamics influenced by land use changes. Moreover, the study utilized a "scenario-actor" policy analysis framework to propose low-carbon strategies through the integration of land use management within territorial spatial planning. The research findings were as follows： ① The carbon source capacity in the study area significantly surpassed its carbon sink capacity. The overall carbon budget concentration index had yet to exceed the 0.4 "alert threshold," with spatial concentration levels as follows： Hangzhou > Huangshan > Shaoxing > Quzhou > Jiaxing ≈ Huzhou. ② For croplands, larger areas and greater shape regularity contributed to a reduction in carbon budgets. Conversely, for constructed lands, expansive areas and increased fragmentation intensified the carbon budget levels, primarily driven by other urban land categories. ③ An increased proportion of croplands and higher land use heterogeneity promoted spatial equilibrium in carbon budgets, whereas the larger coverage and fragmentation of industrial and other urban lands led to an uneven spatial distribution of carbon budgets. ④ Low-carbon optimization of territorial space needs to adjust for the structure and form of carbon source functional land use as a key driver. At the policy implementation level, the central government and urban residents demonstrated strong support for low-carbon territorial control. However, cooperation from local governments, enterprises, and rural residents was suboptimal, necessitating complementary policies for effective guidance. This study holds practical significance for enhancing land use efficiency and promoting low-carbon urban development.

Assessing methane emissions and soil carbon stocks in the Camargue coastal wetlands: Management implications for climate change regulation.

Coastal wetlands are crucial in climate change regulation due to their capacity to act as either sinks or sources of carbon, resulting from the balance between greenhouse gas (GHG) emissions, mainly methane (CH4), and soil carbon sequestration. Despite the paramount role of wetlands in climate regulation few studies investigate both aspects. The Camargue is one of the largest wetlands in Europe, yet the ways in which environmental and anthropic factors drive carbon dynamics remain poorly studied. We examined GHG emissions and soil organic carbon (SOC) stocks and accumulation rates in twelve representative wetlands, including two rice fields, to gain insights into the carbon dynamics and how it is influenced by hydrology and salinity. Mean CH4 rates ranged between - 87.0 and 131.0 mg m-2 h-1and the main drivers were water conductivity and redox, water table depth and soil temperature. High emission rates were restricted to freshwater conditions during summer flooding periods whereas they were low in wetlands subjected to summer drought and water conductivity higher than 10 mS cm-1. Nitrous oxide emissions were low, ranging from - 0.5 to 0.9 mg N2O m-2 h-1. The SOC stocks in the upper meter ranged from 17 to 90 Mg OC ha-1. Our research highlights the critical role of low-saline wetlands in carbon budgeting which potentially are large sources of CH4 but also contain the largest SOC stocks in the Camargue. Natural hydroperiods, involving summer drought, can maintain them as carbon sinks, but altered hydrology can transform them into sources. Artificial freshwater supply during summer leads to substantial CH4 emissions, offsetting their SOC accumulation rates. In conclusion, we advocate for readjusting the altered hydrology in marshes and for the search of management compromises to ensure the compatibility of economic and leisure activities with the preservation of the inherent climate-regulating capacity of coastal wetlands.

Spatiotemporal heterogeneity of lake carbon dioxide flux leads to substantial uncertainties in regional upscaling estimates.

Limited field samplings result in significant uncertainties in regional and global estimates of lake carbon dioxide (CO2) emissions. However, quantitative analysis of uncertainty in regional lake CO2 emission estimates remains unclear. In this study, we utilized satellite data to estimate carbon dioxide flux from 113 eastern China lakes, revealing substantial spatial and temporal variations in flux, averaging 18.07 ± 81.83 mg m-2 d-1. Additionally, satellite-estimated total CO2 effluxes indicated previous upscaling studies had overestimated total CO2 effluxes from these studied lakes by approximately 3-11 times, primarily due to substantial variations in lake CO2 fluxes. Insufficient sampling resolution resulted in considerable uncertainty in upscaling estimations. Temporal variations in carbon dioxide contributed greater upscaling uncertainties than spatial variations in carbon dioxide. To capture the dynamics of lake CO2, increasing the number of sampling points and events is necessary as lake size decreases and trophic state increases. Finally, we propose a prediction for the optimal sampling resolution based on lake area and trophic state, recommending an average of 5 points per lake and bi-monthly sampling as the ideal resolution for similar shallow eutrophic lakes. This approach has been validated as effective in lakes across North America and Europe. We believe that future global-scale lake carbon budget estimates would benefit from field observations conducted at more reasonable sampling points and frequency.

Greenhouse gas fluxes of different land uses in mangrove ecosystem of East Kalimantan, Indonesia.

BACKGROUND: Mangrove ecosystems exhibit significant carbon storage and sequestration. Its capacity to store and sequester significant amounts of carbon makes this ecosystem very important for climate change mitigation. Indonesia, owing to the largest mangrove cover in the world, has approximately 3.14 PgC stored in the mangroves, or about 33% of all carbon stored in coastal ecosystems globally. Unfortunately, our comprehensive understanding of carbon flux is hampered by the incomplete repertoire of field measurement data, especially from mangrove ecosystem-rich regions such as Indonesia and Asia Pacific. This study fills the gap in greenhouse gases (GHGs) flux studies in mangrove ecosystems in Indonesia by quantifying the soil CO2 and CH4 fluxes for different land use types in mangrove ecosystems, i.e., secondary mangrove (SM), restored mangrove (RM), pond embankment (PE) and active aquaculture pond (AP). Environmental parameters such as soil pore salinity, soil pore water pH, soil temperature, air temperature, air humidity and rainfall are also measured. RESULTS: GHG fluxes characteristics varied between land use types and ecological conditions. Secondary mangrove and exposed pond embankment are potential GHG flux sources (68.9 ± 7.0 and 58.5 ± 6.2 MgCO2e ha- 1 yr- 1, respectively). Aquaculture pond exhibits the lowest GHG fluxes among other land use types due to constant inundation that serve as a barrier for the release of GHG fluxes to the atmosphere. We found weak relationships between soil CO2 and CH4 fluxes and environmental parameters. CONCLUSIONS: The data and information on GHG fluxes from different land use types in the mangrove ecosystem will be of importance to accurately assess the potential of the mangrove ecosystem to sequester and emit GHGs. This will support the GHG emission reduction target and strategy that had been set up by the Indonesian Government in its Nationally Determined Contributions (NDC) and Indonesia's 2030 Forest and Other Land Use (FOLU) Net Sink.

Soil environmental anomalies dominate the responses of net ecosystem productivity to heatwaves in three Mongolian grasslands.

Climate change is causing more frequent and intense heatwaves. Therefore, it is important to understand how heatwaves affect the terrestrial carbon cycle, especially in grasslands, which are especially susceptible to climate extremes. This study assessed the impact of naturally occurring, simultaneous short-term heatwaves on CO2 fluxes in three ecosystems on the Mongolia Plateau: meadow steppe (MDW), typical steppe (TPL), and shrub-grassland (SHB). During three heatwaves, net ecosystem productivity (NEP) was reduced by 86 %, 178 %, and 172 % at MDW, TPL, and SHB, respectively. The changes in ecosystem respiration, gross primary production, evapotranspiration, and water use efficiency were divergent, indicating the mechanisms underlying the observed NEP decreases among the sites. The impact of the heatwave in MDW was mitigated by the high soil water content, which enhanced evapotranspiration and subsequent cooling effects. However, at TPL, insufficient soil water led to combined thermal and drought stress and low resilience. At SHB, the ecosystem's low tolerance to an August heatwave was heavily influenced by species phenology, as it coincided with the key phenological growing phase of plants. The potential key mechanism of divergent NEP response to heatwaves lies in the divergent stability and varying importance of environmental factors, combined with the specific sensitivity of NEP to each factor in ecosystems. Furthermore, our findings suggest that anomalies in soil environment, rather than atmospheric anomalies, are the primary determinants of NEP anomalies during heatwaves. This challenges the conventional understanding of heatwaves as a discrete and ephemeral periods of high air temperatures. Instead, heatwaves should be viewed as chronologically variable, compound, and time-sensitive environmental stressors. The ultimate impact of heatwaves on ecosystems is co-determined by a complex interplay of environmental, biological, and heatwave features.

Carbon budget of diversified cropping systems in southwestern China: Revealing key crop categories and influencing factors under different classifications.

Cropping systems are considered the largest source of agricultural GHG emissions. Identifying key categories and factors affecting cropping systems is essential for reducing these emissions. Most studies have focused on the carbon budget of cropping systems from the perspective of a single crop or crop category. Comprehensive studies quantifying the carbon budget of diversified cropping systems, including farmland and garden crops, are still limited. This study aims to fill this gap by quantifying the carbon budget of diversified cropping systems, clarifying their carbon attributes, and identifying key crop categories and influencing factors within different classifications of the system. This study analyzed the carbon budget of a diversified cropping system consisting of 19 crops in Yunnan Province, southwestern China, using a crop-based net greenhouse gas balance methodology based on the "cradle-to-farm" life cycle idea. Crops were categorized into three levels of categories to assess the potential impact of categorization within the cropping system on its carbon balance. Results showed that Yunnan's diversified cropping system is a significant carbon sink, with net sequestration of 33.1 Mt CO2 eq, total emissions of 37.4 Mt CO2 eq, and total sequestration of 70.5 Mt CO2 eq. Cereals, vegetables, and hobby crops were the main contributors to carbon emissions, accounting for 41.61%, 21.87%, and 15.37%, respectively. Cereal crops also made the largest contribution to carbon sequestration at 53.18%. Bananas had the highest emissions per unit area (11.45 t CO2 eq ha-1), while walnuts had the highest sequestration (20.64 t CO2 eq ha-1). In addition, this study highlights effective strategies to reduce greenhouse gas emissions, such as reducing nitrogen fertilizer use, minimizing reactive nitrogen losses, and controlling methane emissions from rice fields. By elucidating the impact of carbon dynamics and crop categories, this study provides insights for sustainable agricultural practices and policies.

Carbon fluxes of China's coastal wetlands and impacts of reclamation and restoration.

Coastal wetlands play an important role in regulating atmospheric carbon dioxide (CO2) concentrations and contribute significantly to climate change mitigation. However, climate change, reclamation, and restoration have been causing substantial changes in coastal wetland areas and carbon exchange in China during recent decades. Here we compiled a carbon flux database consisting of 15 coastal wetland sites to assess the magnitude, patterns, and drivers of carbon fluxes and to compare fluxes among contrasting natural, disturbed, and restored wetlands. The natural coastal wetlands have the average net ecosystem exchange of CO2 (NEE) of -577 g C m-2 year-1, with -821 g C m-2 year-1 for mangrove forests and -430 g C m-2 year-1 for salt marshes. There are pronounced latitudinal patterns for carbon dioxide exchange of natural coastal wetlands: NEE increased whereas gross primary production (GPP) and respiration of ecosystem decreased with increasing latitude. Distinct environmental factors drive annual variations of GPP between mangroves and salt marshes; temperature was the dominant controlling factor in salt marshes, while temperature, precipitation, and solar radiation were co-dominant in mangroves. Meanwhile, both anthropogenic reclamation and restoration had substantial effects on coastal wetland carbon fluxes, and the effect of the anthropogenic perturbation in mangroves was more extensive than that in salt marshes. Furthermore, from 1980 to 2020, anthropogenic reclamation of China's coastal wetlands caused a carbon loss of ~3720 Gg C, while the mangrove restoration project during the period of 2021-2025 may switch restored coastal wetlands from a carbon source to carbon sink with a net carbon gain of 73 Gg C. The comparison of carbon fluxes among these coastal wetlands can improve our understanding of how anthropogenic perturbation can affect the potentials of coastal blue carbon in China, which has implications for informing conservation and restoration strategies and efforts of coastal wetlands.

Greenhouse gases emissions and carbon budget estimation in horizontal subsurface flow constructed wetlands with different plant species.

Constructed wetlands (CWs) are pivotal for wastewater treatment due to their high efficiency and numerous advantages. The impact of plant species and diversity on greenhouse gas (GHG) emissions from CWs requires a more comprehensive evaluation. Moreover, controversial perspectives persist about whether CWs function as carbon sinks or sources. In this study, horizontal subsurface flow (HSSF) CWs vegetated with Cyperus alternifolius, Typhae latifolia, Acorus calamus, and the mixture of these three species were constructed to evaluate pollutant removal efficiencies and GHG emissions, and estimate carbon budgets. Polyculture CWs can stably remove COD (86.79 %), NH4+-N (97.41 %), NO3--N (98.55 %), and TP (98.48 %). They also mitigated global warming potential (GWP) by suppressing N2O emissions compared with monoculture CWs. The highest abundance of the Pseudogulbenkiania genus, crucial for denitrification, was observed in polyculture CWs, indicating that denitrification dominated in nitrogen removal. While the highest nosZ copy numbers were observed in CWs vegetated with Cyperus alternifolius, suggesting its facilitation of denitrification-related microbes. Selecting Cyperus alternifolius to increase species diversity is proposed for simultaneously maintaining the water purification capacity and reducing GHG emissions. Carbon budget estimations revealed that all four types of HSSF CWs were carbon sinks after six months of operation, with carbon accumulation capacity of 4.90 ± 1.50 (Cyperus alternifolius), 3.31 ± 2.01 (Typhae latifola), 1.78 ± 1.30 (Acorus calamus), and 2.12 ± 0.88 (polyculture) kg C/m2/yr. This study implies that under these operation conditions, CWs function as carbon sinks rather than sources, aligning with carbon peak and neutrality objectives and presenting significant potential for carbon reduction efforts.

Carbon budget at the individual-tree scale: dominant Eucalyptus trees partition less carbon belowground.

Large trees in plantations generally produce more wood per unit of resource use than small trees. Two processes may account for this pattern: greater photosynthetic resource use efficiency or greater partitioning of carbon to wood production. We estimated gross primary production (GPP) at the individual scale by combining transpiration with photosynthetic water-use efficiency of Eucalyptus trees. Aboveground production fluxes were estimated using allometric equations and modeled respiration; total belowground carbon fluxes (TBCF) were estimated by subtracting aboveground fluxes from GPP. Partitioning was estimated by dividing component fluxes by GPP. Dominant trees produced almost three times as much wood as suppressed trees. They used 25 ± 10% (mean ± SD) of their photosynthates for wood production, whereas suppressed trees only used 12 ± 2%. By contrast, dominant trees used 27 ± 19% of their photosynthate belowground, whereas suppressed trees used 58 ± 5%. Intermediate trees lay between these extremes. Photosynthetic water-use efficiency of dominant trees was c. 13% greater than the efficiency of suppressed trees. Suppressed trees used more than twice as much of their photosynthate belowground and less than half as much aboveground compared with dominant trees. Differences in carbon partitioning were much greater than differences in GPP or photosynthetic water-use efficiency.

Amendment of straw with decomposing inoculants benefits the ecosystem carbon budget and carbon footprint in a subtropical wheat cropping field.

The incorporation of straw with decomposing inoculants into soils has been widely recommended to sustain agricultural productivity. However, comprehensive analyses assessing the effects of straw combined with decomposing inoculants on greenhouse gas (GHG) emissions, net primary production (NPP), the net ecosystem carbon budget (NECB), and the carbon footprint (CF) in farmland ecosystems are scant. Here, we carried out a 2-year field study in a wheat cropping system with six treatments: rice straw (S), a straw-decomposing Bacillus subtilis inoculant (K), a straw-decomposing Aspergillus oryzae inoculant (Q), a combination of straw and Bacillus subtilis inoculant (SK), a combination of straw and Aspergillus oryzae inoculant (SQ), and a control with no rice straw or decomposing inoculant (Control). We found that all the treatments resulted in a positive NECB ranging between 838 and 5065 kg C ha-1. Relative to the Control, the S treatment increased CO2 emissions by 16%, while considerably enhancing the NECB by 349%. This difference might be attributed to the straw C input and an increase in plant productivity (NPP, 30%). More importantly, in comparison to that in S, the NECB in SK and SQ significantly increased by 27-35% due to the positive response of NPP to the decomposing inoculants. Although the combination of straw and decomposing inoculants yielded a 3% increase in indirect GHG emissions, it also exhibited the lowest CF (0.18 kg CO2-eq kg-1 of grain). This result was attributed to the synergistic effects of straw and decomposing inoculants, which reduced direct N2O emissions and increased wheat productivity. Overall, the findings of the present study suggested that the combined amendment of straw and decomposing inoculants is an environmentally sustainable management practice in wheat cropping systems that can generate win-win scenarios through improvements in soil C stock, crop productivity, and GHG mitigation.

Particle-attached bacteria act as gatekeepers in the decomposition of complex phytoplankton polysaccharides.

BACKGROUND: Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity, and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome, and metaproteome analyses. RESULTS: Prominent active 0.2-3 µm free-living clades comprised Aurantivirga, "Formosa", Cd. Prosiliicoccus, NS4, NS5, Amylibacter, Planktomarina, SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae, Nitrincolaceae, Methylophagaceae, Sulfitobacter, NS9, Polaribacter, Lentimonas, CL500-3, Algibacter, and Glaciecola dominated 3-10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria. CONCLUSIONS: Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. Video Abstract.

The contribution of carbon budget to masting intervals in Veratrum album populations inhabiting different elevations.

PREMISE: Mast flowering/seeding is often more extreme in lower-resource environments, such as alpine compared to lowland habitats. We studied a masting herb that had less extreme masting at higher elevations, and tested if this difference could be explained by higher photosynthetic productivity and/or lower reproductive investment at the higher-elevation sites. METHODS: We examined the relationship between flowering intervals and carbon budget (i.e., the balance between reproductive investment and annual carbon fixation) in a masting herb, Veratrum album subsp. oxysepalum, across five lowland and six alpine populations in northern Japan. We evaluated the previous flowering histories of individual plants based on rhizome morphology and analyzed the masting patterns of individual populations. Total mass of the reproductive organs, as a proxy of reproductive investment, was compared between the lowland and alpine populations. Annual carbon fixation was estimated on the basis of photosynthetic capacity, total leaf area per plant, and seasonal transition of light availability. RESULTS: Interval between high-flowering years was shorter and total reproductive investment was smaller in the alpine than in the lowland populations. Owing to its high photosynthetic capacity and continuous bright conditions, annual carbon fixation per plant was 1.5 times greater in alpine habitat than in lowland habitat. These results suggest that V. album alpine populations have shorter flowering intervals than lowland populations due to faster recovery from energy loss after reproduction. CONCLUSIONS: Our study demonstrated that masting intervals in V. album populations can be explained by habitat-specific carbon budget balances.

Characteristics of carbon budget based on energy carbon emissions and vegetation carbon absorption.

How to evaluate the change characteristics of energy carbon emissions (ECE) and vegetation carbon absorption (VCA) by scientific methods is particularly important for achieving carbon peak by 2030 and carbon neutrality by 2060. Based on provincial-level energy consumption data, nighttime light data, and population data, this study realized spatial simulation of energy carbon emissions and analyzed the change characteristics of energy carbon emissions (ECE) and vegetation carbon absorption (VCA) combined with the net primary productivity (NPP)of vegetation. Besides, the relationship between energy carbon emissions, vegetation carbon absorption, and economic development was also analyzed at an urban scale. The results showed that (1) the total ECE increased from 4.34 billion tons in 2000 to 14.43 billion tons in 2019, but the growth rate of ECE decreased from 15.9% during 2000-2010 to 3.1% during 2010-2019. The VCA capacity has been increasing year by year. In 2019, it could absorb 1.56 billion tons more carbon dioxide than in 2000 with an increase of 16.1%. (2) Through the identification of the increasing and decreasing regions of ECE and VCA, it was found that the continuous rise area of ECE accounts for 0.5% of the study area; the area of fluctuating rise accounted for 6.7% of the study area. The area of continuous decline of VCA accounted for 0.2% of the study area; the area of fluctuating decline accounted for 49.6% of the study area. (3) The eastern China accounted for 42% of ECE and 17% of VCA with 11.4% of land, while the western region accounted for 26% of ECE and 55% of VCA with 66.6% of land, which indicated that there were significant differences in the characteristics of carbon budget between the eastern China and the western region. (4) The carbon pressure index (CPI) of most cities was on the rise, but the carbon efficiency index (CEI) was also on the rise, and cities were developing towards the model of low energy consumption and high output value. In a word, the growth rate of ECE is slowing down, and the VCA capacity is increasing. In the process of promoting carbon neutrality, we should be aware of the different resource endowments of different regions, realize the actual role of each region in carbon neutrality and economic development, and allocate carbon neutrality tasks differently.