Cumulative CO2 Emissions Research Articles

High starch and hemicellulose labile C degradation functional genes increase soil CO2 emissions follow straw return

Straw return is a key method to regulate soil carbon (C) by microbial utilization accumulating and CO2 releasing, which mainly depends on microbial metabolism processes. The present knowledge of the mode and mechanism of soil CO2 emission under straw return is limited. We established four straw return treatments, including straw shallow return (SS, 0–20 cm), straw subsoil burial (SD, 20–40 cm), straw mulching (SM), and control with no straw (NS). Microbial metabolic limitation and the abundance of C degradation functional genes were quantified using enzyme stoichiometry and high-throughput quantitative PCR-based chip technology, respectively. The results revealed that the addition of straw inputs resulted in an increase in soil nutrient contents and soil CO2 emissions. The cumulative CO2 emissions of SS and SM treatments were 21,013.53 and 20,819.26 kg hm−2, respectively, which significantly increased by 4.70 % and 3.73 % compared with SD treatment. Compared with SM and SD treatments, microbial C and P limitations of SS treatment were significantly enhanced, increasing by 1.15 %–1.20 % and 2.73 %–1.21 %, respectively. Straw return increased the absolute abundance of genes engaged in decomposing diverse C source compounds, although with a reduction in microbial C use efficiency. The absolute abundance of amyA, apu, sga, abfA, xylA, and manB labile C degradation genes was higher in SM than in SD treatment, increasing by 1.11 %–25.88 %. On the contrary, the absolute abundance of glx and lig recalcitrant C degradation genes was lower in SM than in SD treatment, reducing by 2.96 %–3.68 %. Straw return directly impacts soil nutrient contents and indirectly influences microbial biomass carbon (MBC), nutrient limitation, and C degradation genes, as revealed by the partial least squares pathway model, ultimately leading to changes in soil CO2 emissions. This finding should contribute to the enhancement of soil C retention and the selection of appropriate methods for straw incorporation in tillage fields.

Carbon footprint and associated environmental impacts of fisheries on the Pulicat region, Southern India: A preliminary study

The current research analyzed carbon emissions resulting from fossil fuel consumption in the Pulicat region. This area is home to approximately 3500 motorized boats dedicated to fishing activities. Through this comprehensive study, we assessed the fuel consumption and subsequent carbon emissions within the motorized fishing sector. Our investigation revealed that traditional fishing methods in Pulicat Lake consumed 148,515 L of fuel whereas fishing methods along the Pulicat coast consumed a substantial 1650,429 L of fuel during the study period spanning from June 2022 to May 2023. In total, the Pulicat region accounted for the consumption of 1798,944 L (1547.1 metric tonnes (MT)) of fuel, contributing a mere 0.00004% to the global fuel consumption levels attributed to the small-scale fishing sector. Furthermore, the cumulative CO2 emissions resulting from fishing activities in the Pulicat region amounted to 4731.23 MT, representing a 0.001% of the overall CO2 emissions attributed to the Indian fishing sector. Remarkably, the Pulicat region emitted 1.05 MT of CO2 to capture 1 t of fish during the study period. The average CO2 emissions of fish stood at 1.08 MT of CO2/ ton of fish. Our analysis revealed that October 2022 recorded the highest carbon emissions per ton of fish at 1.45 MT of CO2 whereas May 2023 exhibited the lowest carbon emissions at 0.54 MT of CO2/ ton of fish. Within the Pulicat region, the use of crab lift net fishing methods in the lake (0.10 MT of CO2 per ton of fish) and purse seine techniques along the coast (0.65 MT of CO2/ ton of fish) emerged as the most energy-efficient fishing methods among the various alternatives. This study offers an in-depth exploration of carbon emissions originating from the Pulicat region’s fishing activities, providing valuable insights into the environmental impact of this crucial sector.

Soil Gaseous Carbon Emissions from Lettuce Fields as Influenced by Different Irrigation Lower Limits and Methods

Lettuce is a water-sensitive stem-used plant, and its rapid growth process causes significant disturbances to the soil. Few studies have focused on the gaseous carbon emissions from lettuce fields under different irrigation methods. Therefore, this study investigated the effect of different drip-irrigation lower limits and methods (drip and furrow irrigation) on greenhouse gas (CO2, CH4) emissions from lettuce fields. Thus, drip irrigation (DI) was implemented using three different lower limits of irrigation corresponding to 75%, 65%, and 55% of the field capacity, and named DR1, DR2, and DR3, respectively. Furrow irrigation (FI) was used as a control treatment. The CO2 and CH4 emission fluxes, soil temperature, and soil enzyme activities were detected. The results showed that the cumulative CO2 emission was highest under DR3 and relatively lower under DR1. For the FI treatment, the cumulative CO2 emission (382.7 g C m−2) was higher than that under DR1 but 20.2% lower than that under DR2. The cumulative CH4 emissions under FI (0.012 g C m−2) were the greatest in the whole lettuce growth period, while DR2 and DR3 treatments emitted lower amounts of CH4. The irrigation method considerably enhanced the activity of urease and catalase, meanwhile promoting CO2 emission. The low irrigation amount each time combined with high irrigation frequency reduced soil CO2 emission while increasing CH4 emission. From the perspective of the total reduction of gaseous carbon, DR1 is the optimal drip irrigation method among all the irrigation lower limits and methods.

Suppression of Carbon Dioxide Emissions from Soil Amended with Autoclaved Lightweight Aerated Concrete Under Different Compaction and Moisture Conditions

Carbon dioxide (CO2) emissions has been highlighted worldwide as a contributor to the greenhouse effect. Soil physical characteristics such as bulk density and moisture content can influence the emissions of greenhouse gasses (GHGs) from soil. Soil conditioners applied to soil can also affect the terrestrial CO2 emissions. Autoclaved lightweight aerated concrete (ALC) is in use at present as a soil conditioner or calcium silicate fertilizer, it is a type of porous material made from industrial waste. In this study, we determined the effect of ALC (Inenica, Clion Co., Ltd, Japan) on CO2 emissions from paddy soil with considering soil compaction and moisture content. Laboratory experiments were conducted using soils with and without ALC (0 and 5%), under two levels of compaction (compacted and non-compacted), and two soil moisture contents (60% and 100% water holding capacity: WHC) in 200 mL glass vials. All treatments with triplicates were incubated at 25° C for 21 days under aerobic conditions. Emissions of CO2 were determined at 0, 1, 3, 7, 14, and 21 days using gas chromatography with the thermal conductivity detector. The addition of ALC significantly decreased CO2 emissions from soil at the early stages of incubation. Emissions of CO2 were significantly lower at 100% WHC than at 60% WHC. Non-compacted treatments showed significantly higher emissions of CO2 than compacted treatments during the incubation time period. This is possibly due to improved soil aeration and porosity, which enhanced the activity of soil microorganisms responsible for the decomposition of organic matter. The interactions between moisture content with ALC addition and compaction on cumulative CO2 emissions were statistically significant (p<0.05). The effect of ALC addition on CO2 suppression was more effective at compacted and 100% WHC (51% reduction compared with control). Our study suggested that precise dosage of ALC application (5%) can effectively reduce CO2 emissions from soil, under 100% WHC and compaction conditions than 60% WHC and non-compaction conditions.
 
 Keywords: Aerobic, Autoclaved lightweight aerated concrete, Carbon dioxide, Compaction, Moisture content

Polyethylene microplastic-induced microbial shifts affected greenhouse gas emissions during litter decomposition in coastal wetland sediments

Microplastic contamination has become increasingly aggravated in coastal environments, further affecting biogeochemical processes involved with microbial community shifts. As a key biogeochemical process mainly driven by microbiota in coastal wetland sediments, litter decomposition contributes greatly to the global greenhouse gas (GHG) budget. However, under microplastic pollution, the relationship between microbial alterations and GHG emissions during litter decomposition in coastal wetlands remains largely unknown. Here, we explored the microbial mechanism by which polyethylene microplastic (PE-MP) influenced greenhouse gas (i.e., CH4, CO2 and N2O) emissions during litter decomposition in coastal sediments through a 75-day microcosm experiment. During litter decomposition, PE-MP exposure significantly decreased cumulative CH4 and CO2 emissions by 41.07% and 25.79%, respectively. However, there was no significant change in cumulative N2O emissions under PE-MP exposure. The bacterial, archaeal, and fungal communities in sediments exhibited varied responses to PE-MP exposure over time, as reflected by the altered structure and changed functional groups of the microbiota. The altered microbial functional groups ascribed to PE-MP exposure and sediment property changes might contribute to suppressing CH4 and CO2 emissions during litter decomposition. This study yielded valuable information regarding the effects of PE-MP on GHG emissions during litter decomposition in coastal wetland sediments.

Zero-valent iron addition stimulated straw-derived carbon accumulation in submerged soil

Soil organic carbon (SOC) is the key indicator of soil fertility, and its stabilization plays a significant role in terrestrial carbon cycling. The turnover of SOC often interacts with iron due to its active redox characteristics, especially in paddy soils. Zero-valent iron (ZVI) is highly reductive, while how its addition controls SOC turning over in soil received less attention and knowledge gap exists on soil C dynamics. Therefore, we investigated the influence of ZVI addition on soil and straw C dynamics in submerged soil over a period of 30 days in an incubation study. The results showed that ZVI addition enhanced the endogenous Fe(III) reduction, and the exogenous ZVI was oxidized mostly to Fe(II), resulting in substantial Fe(II) accumulation, with the content 33.39–164.9% higher than that in non-ZVI treatments after incubation. At the initial stage of incubation during day 0–10, ZVI addition showed a stimulated effect on OC accumulation as both the cumulative CO2 emission and dissolved organic carbon (DOC) released were reduced in ZVI-amended treatments. This could be attributed to the O2 limitation on OC mineralization caused by the lower oxidation-reduction potential (ORP) by ZVI addition. Besides, endogenous Fe(III) reduction boosted by ZVI addition could release fresh surfaces on Fe mineral for C accumulation by forming organics-Fe mineral complexes. During the latter stage of day 10–30, ZVI addition showed an inhibited effect on OC accumulation as both the cumulative CO2 emission and DOC released were increased in ZVI-amended treatments, and CH4 emission was vigorous after a 10-day lag phase. Labile OC was liberated and vulnerable to decomposition by microorganisms due to the dissolution of OC-Fe(III) oxide complexes as Fe(III) reduction was enhanced by ZVI addition. Furthermore, CH4 emission was promoted by ZVI addition through lowering soil ORP and supplying electrons for methanogenesis. ZVI addition mitigated OC decomposition during the initial stage and stimulated that during the latter stage of incubation. Overall, ZVI addition increased straw C accumulation in the form of insoluble carbon (Caccumulated), but the different responses of C dynamic between days 0–10 and 10–30 led to a statistic insignificant positive effect. However, the association between iron oxides and OC was enhanced in ZVI addition treatments due to the anaerobic corrosion of ZVI, which may increase the stability of OC, indicating a potential to accumulate more straw C in the long term.

Multi-objective optimization of saline water irrigation in arid oasis regions: Integrating water-saving, salinity control, yield enhancement, and CO2 emission reduction for sustainable cotton production

Brackish water stands as a promising alternative to mitigate freshwater scarcity in arid regions. However, its application poses potential threats to agricultural sustainability. There is a need to establish a clear understanding of the economic and ecological benefits. We conducted a two-year (2021−2022) field experiment to investigate the effects of four different irrigation water salinity levels on soil electrical conductivity, cotton yield, water use efficiency, CO2 emissions, and carbon sequestration. The salinity levels were designated as CK (0.85 g L−1), S1 (3 g L−1), S2 (5 g L−1), and S3 (8 g L−1). Results indicated that using irrigation water with high salinity (≥5 g L−1) led to the accumulation of salt in the soil, and a decrease in plant biomass and seed cotton yield. Compared to CK, the S3 treatment decreased by 18.72 % and 20.10 % in the respective two years. Interestingly, using brackish water (3 L−1 and 5 g L−1) decreased the rate and cumulative CO2 emissions, and increased the carbon emission efficiency and carbon sequestration by 0.098–0.094 kg kg−1 and 871–1859 kg ha−1 in 2021, 0.098–0.094 kg kg−1 and 617–1995 kg ha−1 in 2022, respectively. To comprehensively evaluate the tradeoff between economic and ecological benefits, we employed the TOPSIS method, and S1 was identified as the optimal irrigation salinity. Through fitting analysis, the most suitable irrigation salinity levels for 2021 and 2022 were determined as 3.52 g L−1 and 3.31 g L−1, respectively. From the perspective of water conservation, salinity management, yield improvement, and reduction of CO2 emissions, it is feasible to utilize brackish water for irrigation purposes, as long as the salinity does not exceed 3.52 g L−1 (first year) and 3.31 g L−1 (second year).

An appropriate amount of straw replaced chemical fertilizers returning reduced net greenhouse gas emissions and improved net ecological economic benefits

With the increasing application of crop straw, the greenhouse gas emissions caused due to crop straw have received increasing attention. However, the current studies have not explored the greenhouse gas emissions from on-farmland consumption of returned straw. Based on a long-term positioning experiment, three treatments were set up in double-cropping rice fields: chemical fertilizer (CF), straw replacing 1/3 nitrogen fertilizer (MS), and straw replacing 2/3 nitrogen fertilizer (HS). We measured the biomass, soil properties, and greenhouse gas emissions of double-cropping rice and then comprehensively evaluated the global warming potential, carbon footprint, and net ecological and economic benefits. The straw treatments (MS and HS) increased the cumulative annual emissions of CH4 (98.44% and 261.23%), CO2 (30.85% and 122.29%), and N2O (7.37% and 52.50%), the cumulative annual global warming potential (74.15% and 206.12%), average GHG intensity (43.26% and 138.07%), and the annual cumulative net ecosystem carbon budget (52.96% and 100.97%) in the early and late rice growing seasons, respectively. We observed that the real-time greenhouse gas emissions were significantly correlated to the soil microbial functional genes and total carbon, NH4+-N, and NO3−-N. The results of the random forest model showed that total carbon (13.87%) and nirK abundance (9.80%) were the highest predictors of global warming potential at the booting and maturity stages, respectively during rice growing season. Combining the resource inputs for agricultural production and the greenhouse gas emission potential of the returned straw on its own, MS showed the lowest net greenhouse gas emission, and MS and HS showed significantly increased annual cumulative net ecological economic benefits (38.08% and 34.30%). Overall, MS showed the lowest net greenhouse gas emission and the highest net ecological economic benefits, which is a straw-returning measure with low environmental impact and high economic returns.

Tillage after irrigation decreases soil N2O but increases CO2 emissions in a rice-wheat rotation system

Increasing attention is paid to mitigate greenhouse gas (GHG) emissions through improvement in agricultural practices. Tillage after irrigation (Wet tillage; WT) can shift soil structure compared with tillage before irrigation (Dry tillage; DT), associated with GHG emissions, while information is limited on the effects of WT on nitrous oxide (N2O) and carbon dioxide (CO2). A two-year field experiment was conducted to assess the effects of the sequence between tillage and irrigation (i.e., WT and DT) on soil methane (CH4), N2O, and CO2 emissions and the underlying mechanisms in a rice-wheat rotation system. The results showed that WT significantly decreased cumulative N2O emissions from the jointing to maturity stage due to a lower abundance of nirS and nirK genes at booting stages, leading to a decrease of 35.1 %–42.6 % for cumulative N2O emissions under WT throughout the whole rice-growing stage (P < 0.05). However, WT increased cumulative CO2 emissions from the jointing to maturity stage due to disturbance for soil aggregation with lower mean weight diameter and geometric mean diameter, resulting in an increase of 18.3 %–19.1 % for cumulative CO2 emissions throughout the whole rice-growing period (P < 0.05) compared with DT. WT had a minor effect on methane (CH4) emissions and rice yield and decreased GHG intensity only in the first year. Our results highlight a trade-off between N2O and CO2 emissions under WT, and a strategic rotation between WT and DT may be a clean practice to sustain the irrespective benefits of WT and DT.

Effect of microplastics on soil greenhouse gas emissions in agroecosystems: Does it depend upon microplastic shape and soil type?

Microplastics have emerged as a significant pollutant in terrestrial ecosystems, with their accumulation in agricultural fields influencing soil greenhouse gas emissions. Nevertheless, the specific impact of microplastics, particularly in relation to their varying shapes, and how this effect manifests across diverse soil types, remains largely unexplored. In this study, a 56-day incubation experiment was conducted to assess the influence of microplastic shapes (fibers, films, and spheres) on CO2 and N2O emissions in three types of soils (Chernozems, Luvisols, and Ferralsols), while also investigating potential associations with the compositional and functional characteristics of soil bacterial communities. When compared to the control group, the introduction of microplastic fibers resulted in an increase of 21.7 % in cumulative CO2 emissions and a 31.4 % rise in cumulative N2O emissions in Ferralsols. This increase was closely linked to the proliferation of the Actinobacteria and Bacilli classes and the orders of Catenulisporales, Bacillales, Streptomycetales, Micrococcales, and Burkholderiales within the bacterial communities of Ferralsols, alongside an observed elevation in N-acetyl-glucosaminidase enzyme activity. The inclusion of microplastic fibers did not result in significant alterations in greenhouse gas emissions within Chernozems and Luvisols. This is likely attributed to the inherent buffering capacity of these soils, which helps stabilize substrate and nutrient availability for microbial communities. These findings highlight that the response of greenhouse gas emissions to microplastic additions is contingent upon the shape of the microplastics and the specific soil types.

Effects of Different Exogenous Organic Substrates on Soil Carbon and Nitrogen Mineralization and Their Priming Effects

The input of exogenous organic matter could affect the transformation of soil carbon (C) and nitrogen (N), and their C- and N-priming effects (CPE and NPE) play a key role in the balance of soil C and N. However, little is known about how the interaction effect between straw and straw biochar regulates CPE and NPE. Therefore, we conducted a 90-day incubation experiment, which included five treatments: no straw and straw biochar (CK), 1.5% straw (S), 0.53% straw biochar (B), 1.5% straw + 0.53% straw biochar (SB), and 1.5% straw + 1.06% straw biochar (SB1). Our findings revealed that cumulative soil CO2 emissions were increased by 95.52–216.53% through the short-term input of exogenous organic matter input; however, this trend gradually weakened with decreasing dissolved organic C (DOC) content. The cumulative NPE generated by the addition of exogenous organic matter was much smaller than the cumulative CPE. Under the B and S treatments, the cumulative CPE and NPE were negative throughout the entire incubation period. The SB treatment remarkably boosted the microbial biomass nitrogen (MBN) content; however, the SB1 treatment was more effective in inhibiting soil C and N mineralization processes than SB treatment. Moreover, the cumulative CPE and NPE were mainly regulated by N. We conclude that the combination of straw and straw biochar preferentially stimulated soil C mineralization, but that this effect decreased with time, which may be due to the consumption of labile DOC caused by the initial positive CPE, while soil N mineralization had a lag effect.

Technical and economic analysis of a multicarrier building energy hub concept with heating loads at different temperature levels

Integration of renewable and waste energy sources, decentralisation, electrification and energy storage, are key pillars of energy transition in the district heating sector. Such a strategy can be implemented at the building level using the multi-carrier energy hub concept, which has recently gained popularity. This paper presents a technical and financial feasibility study of a building-integrated multi-carrier energy hub concept. The case study is performed for an existing large medical centre, where demand occurs simultaneously for electricity, cold, and heat at different temperature levels, including hot process water and steam. The central idea is to replace the high-exergy steam with heat from the municipal district heating network. The concept also includes the integration of heating and cooling loads, heat storage and implementation of an on-site photovoltaic (PV) power plant. The key components of the proposed hub technological structure are high-temperature heat pumps. Five alternative structures of the system configuration are examined using an hour-by-hour annual simulation. The results reveal that the proposed multi-carrier energy hub is fully operational. The project is also profitable, which results mainly from significant energy savings compared to the existing heat supply system using high-pressure steam. However, the profitability strongly depends on the system configuration, and the choice of the best option is ambiguous. The system with heat storage reaches the highest net present value (NPV) while the one without the storage results in the highest internal rate of return (IRR) due to significantly lower capital expenditures (CAPEX). In all cases, the project leads to a considerable cumulative CO2 emissions reduction, which is at the level of 1351 up to 2961 tons annually depending on system configuration.

Response of soil CO2 emissions and water-carbon use efficiency of winter wheat to different straw returning methods and irrigation scenarios.

The shortage of water resources and the increase of greenhouse gas emissions from soil seriously restrict the sustainable development of agriculture. Under the premise of ensuring a stable yield of winter wheat through a reasonable irrigation scenario, identifying a suitable straw returning method will have a positive effect on agricultural carbon sequestration and emission reduction in North China Plain. Straw burying (SR) and straw mulching (SM) were adopted based on traditional tillage under in the winter wheat growing season of 2020-2021 and 2021-2022. Three irrigation scenarios were used for each straw returning method: no irrigation (I0), irrigation 60 mm at jointing stage (I1), and irrigation of 60 mm each at the jointing and heading stages (I2). Soil moisture, soil respiration rate, cumulative soil CO2 emissions, yield, water use efficiency (WUE) and soil CO2 emission efficiency (CEE) were mainly studied. The results showed that, compared to SM, SR improved the utilization of soil water and enhanced soil carbon sequestration. SR reduced soil respiration rate and cumulative soil CO2 emissions in two winter wheat growing seasons, and increased yield by increasing spike numbers. In addition, with an increase in the amount of irrigation, soil CO2 emissions and yield increased. Under SR-I1 treatment, WUE and CEE were the highest. SR-I1 increases crop yields at the same time as reducing soil CO2 emissions. The combination of SR and irrigation 60 mm at jointing stage is a suitable straw returning irrigation scenario, which can improve water use and reduce soil CO2 emission in NCP. © 2023 Society of Chemical Industry.

Renovated or replaced? Finding the optimal solution for an existing building considering cumulative CO2 emissions, energy consumption and costs – A case study

The buildings sector is responsible for 37 % of global final energy consumption and nearly 40 % of total direct and indirect CO2 emissions. This has led to promoting renovation efforts to decrease operational emissions of the existing building stock. With decreasing operational emissions, embodied emissions are becoming more important. In new buildings, embodied emissions account for about half of total emissions through the life cycle of a building. If both embodied and operational emissions are considered, renovation often outperforms new constructions, due to high embodied emissions of the structure - especially solid construction with a basement. Based on this, the decision if a building should be renovated or replaced is often not straight forward and depends on various factors. In this paper, a typical German building was considered as a case study, for which both renovation and replacement scenarios were considered, to identify the optimal solutions in terms of overall energy consumption and CO2 emissions of the building in the use phase, the environmental impacts of the building along its entire life cycle, and related costs. Results show that the lowest CO2 emissions during the lifetime of the analyzed building can be achieved with a sustainable replacement building (-2.05 kg CO2/m2/year) by using a heat pump with ground collector coupled with PV. This allows, compared to the existing reference building, reductions of 97 % and 101 % in terms of energy consumption and CO2 emissions, respectively; while natural gas-based technologies are the least targeted and the most volatile to fuels’ prices changes over the years.

Responses of soil greenhouse gas emissions to soil mesofauna invasions and its driving mechanisms in the alpine tundra: A microcosm study

Climate change is resulting in significant modifications of the altitudinal patterns of soil fauna in mountains, leading to their upward invasion and alteration of soil ecological processes. However, the effects of soil greenhouse gas (GHG) emissions from soil mesofauna invasion and their driving mechanisms have not been clearly understood. To address this knowledge gap, we simulated a soil mesofauna invasion from an Erman's birch forest (EB) to the alpine tundra (AT) of the Changbai Mountain in Northeast China. Four treatments were established: no soil mesofauna (S0), native species (SN), invasive species (SI), and invasive species superposed native species (SS). We conducted a 79-day microcosm experiment, utilizing gas chromatography and high-throughput sequencing, to explore the variations in soil greenhouse gas emissions and their driving factors. Results showed that the cumulative CO2 emissions under SN, SI, and SS, compared with S0, increased by 34.13 %, 73.93 %, and 107.64 % and cumulative N2O emissions increased by 59.05 %, 101.18 %, and 183.88 %, respectively. Compared to SN, the cumulative emissions of CO2 and N2O increased by 29.89 % and 26.31 % under SI and by 54.91 % and 78.59 % under SS, respectively. The impacts of invasive species and native species on greenhouse gases were not a simple additive effect. Abiotic (soil variables) and biotic (soil mesofauna and microbial diversity) factors explained 37.76 % and 44.41 % of the total variations in CO2 and N2O emissions, respectively, in which NH4+-N and C: N ratios contributed the largest variations. The contribution of soil mesofauna diversity to the variations in CO2 and N2O emissions was higher than that of microbial diversity. The bacterial network graph density was correlated with soil CO2 and N2O emissions. Our findings highlight that soil mesofauna invasions increased GHG emissions, and these variations were predominantly explained by biotic rather than abiotic factors.

Carbon Dioxide and Nitrous Oxide Emissions from a Typical Sugarcane Soil in the Cauca River Valley, Colombia

Sugarcane is an important crop for tropical countries and to accurately inventory its greenhouse gas (GHG) emissions baseline measurements are needed. In Colombia, sugarcane is one of the most important crops in terms of cultivated area and, paradoxically, scientific information reporting GHG emissions based on field measurements is almost nonexistent. The objective of this work was to quantify the direct emissions of carbon dioxide (CO2) and nitrous oxide (N2O) in the sugarcane-soil system of the Cauca river valley, Colombia. For this purpose, a field experiment was established in a typic haplustert soil cropped with sugarcane. The effects of nitrogen (N) fertilization and sampling site on its GHG emissions were tested using the closed static chamber method over a period of 211 days. The main cumulative emissions were 765.14 ± 34.1 g CO2–C m−2 and 125.4 ± 22.6 mg N2O–N m−2. Overall, GHG emissions were modified by N fertilization, the sampling site, and their interaction. Nitrogen fertilization with urea increased mean and cumulative CO2 and N2O emissions, especially at the row sampling site. This paper highlights the importance of considering these factors when the quantification of GHGs or a reduction of their associated uncertainties are required. This work reportss the first GHG emissions data for a typical sugarcane agroecosystem in Colombia.

Adding Corbicula fluminea altered the effect of plant species diversity on greenhouse gas emissions and nitrogen removal from constructed wetlands in the low-temperature season

Plant species diversity is crucial in greenhouse gas emissions and nitrogen removal from constructed wetlands (CWs). However, previous studies have overlooked the impact of benthos on cumulative greenhouse gas emissions during the low-temperature season in CWs. In this study, we established 66 vertical flow CWs with three levels of species richness (1, 2, and 4 species) and eleven species compositions. The Corbicula fluminea was added or not added at each diversity level and monitored greenhouse gas emissions and effluent nitrogen concentration. Our findings indicated that (1) in microcosms without C. fluminea, high species richness significantly increased effluent nitrogen concentrations (NO3−-N, NH4+-N, and TIN), but plant species richness did not affect cumulative CH4, N2O, and CO2 emissions. The presence of Hemerocallis fulva significantly increased cumulative CO2 emissions, while the presence of Iris tectorum significantly increased effluent nitrogen (NO3−-N and TIN) concentrations and cumulative N2O emissions; (2) in microcosms with C. fluminea, the lowest cumulative CH4 emissions occurred when there were two species, but plant species richness did not affect cumulative CO2 and N2O emissions. The presence of H. fulva significantly increased cumulative CH4 emissions, while the presence of Reineckea carnea significantly increased effluent nitrogen (NO3−-N, NH4+- N, TIN) concentrations; (3) at the same diversity level, the addition of C. fluminea significantly increased cumulative CH4 and N2O emissions, as well as effluent nitrogen concentrations. These results demonstrate that C. fluminea alters the effect of plant species diversity on cumulative greenhouse gas emissions and nitrogen removal from CWs during the low-temperature season. We recommend using a two-species mixture to reduce greenhouse gas emissions. However, we caution against using plant compositions with H. fulva or I. tectorum for effective wastewater treatment and greenhouse gas reduction in CWs.

Earthworms increase soil greenhouse gas emissions reduction potential in a long-term no-till Mollisol

Earthworm activity and plant residues in the soil can strongly influence soil organic carbon (SOC) dynamics. However, studies on how earthworms, especially epigeic and endogeic species alone or together, affect the main soil greenhouse gas (GHG) emissions (CO2 and N2O) and SOC under the long-term no-till (NT) and conventional tillage (CT) in Mollisols in Northeast China are unclear. The effects of two different species of earthworms (epigeic, Eisenia nordenskioldi; endogeic, Metaphire tschiliensis) on the soil GHG emissions and the SOC content were studied in NT and CT soils in a 337-day mesocosm experiment. The presence of earthworms enhanced the soil cumulative CO2 and N2O emissions in both NT and CT soils, and the soil GHG emissions (expressed in terms of the global warming potential, GWP) were increased by 20.43 %–42.99 % in NT soil and by 0–55.62 % in CT soil, respectively. Compared to E. nordenskioldi, the presence of M. tschiliensis (endogeic species) significantly increased soil GHG emissions. Earthworms in NT soil induced less soil GHG emissions than those in CT soil. The presence of earthworms did not increase the SOC content in CT soil but significantly increased the SOC content in NT soil. Our study suggests that earthworms in the long-term no-till soil can contribute to the reduction of soil GHG emissions. This research helps to understand the effects of different ecological categories of earthworms on soil GHG emissions and SOC dynamics under different tillage systems and to mitigate soil GHG emissions.

Double-cropping, tillage and nitrogen fertilization effects on soil CO2 and CH4 emissions

Double-cropping is increasingly embraced for its economic advantages in irrigated crops within the Ebro Valley region. However, the implications of this practice for soil carbon dioxide (CO2) and methane (CH4) emissions remain poorly understood. This study aimed to assess the impact of legume-maize double-cropping on soil CO2 and CH4 emissions and to identify optimal tillage systems and nitrogen fertilization rates for enhancing soil carbon budget. Conducted in Agramunt (NE Spain), the research transformed a long-term tillage and nitrogen fertilization field experiment initiated in 1996 under rainfed conditions. It transitioned into a maize monocrop system in 2015 and a diversification experiment in 2018. Maize monocrop was compared to a legume-maize double-cropping with two tillage systems (conventional tillage and no-tillage) and three mineral nitrogen fertilization rates (zero, medium and high). The legumes used were pea for grain (2019), vetch for green manure (2020) and vetch for forage (2021). The use of legumes in the double-cropping system had a significant impact on CO2 fluxes. CO2 emissions in the double-cropping ranged from 250 to 8070 mg CO2-C m−2 day−1, while in the monocropping, the fluxes were in the range of 150–5790 mg CO2-C m−2 day−1. Due to the higher biomass production and extended crop cycle in the double-cropping, along with increased residue decomposition due to the higher amount of residue provided, the cumulative CO2 emissions were higher in the double-cropping. Within the double-cropping, the response of cumulative soil CO2 emissions to tillage depended on the legume used and residue management. For legumes with a low nitrogen content, conventional tillage resulted in lower cumulative CO2 emissions, while for legumes with a high nitrogen content, the lowest emissions were observed in the no-tillage system. The increased incorporation of crop residues in the combined approach of double-cropping and no-tillage led to a greater net ecosystem carbon budget, reaching 1960 kg C ha−1. However, the use of high or medium nitrogen fertilization rates did not have a significant impact on CO2 emissions or the net ecosystem carbon budget. Cumulative soil CH4 emissions were only affected by soil tillage in 2019 and 2021, with greater net CH4 uptake under no-tillage compared with conventional tillage. This work underlines the importance of using legume-maize double-cropping together with no-tillage and N fertilization reduction to control the soil CO2 and CH4 emission yields, while maintaining crop yields under Mediterranean conditions.

Effects of co-applied biochar and plant growth-promoting bacteria on soil carbon mineralization and nutrient availability under two nitrogen addition rates

In the background of climate warming, the demand for improving soil quality and carbon (C) sequestration is increasing. The application of biochar to soil has been considered as a method for mitigating climate change and enhancing soil fertility. However, it is uncertain whether the effects of biochar application on C-mineralization and N transformation are influenced by the presence or absence of plant growth-promoting bacteria (PGPB) and soil nitrogen (N) level. An incubation study was conducted to investigate whether the effects of biochar application (0 %, 1 %, 2 % and 4 % of soil mass) on soil respiration, N status, and microbial attributes were altered by the presence or absence of PGPB (i.e., Sphingobium yanoikuyae BJ1) under two soil N levels (N0 and N1 soils as created by the addition of 0 and 0.2 g kg−1 urea- N, respectively). The results showed that biochar, BJ1 strain and their interactive effects on cumulative CO2 emissions were not significant in N0 soils, while the effects of biochar on the cumulative CO2 emissions were dependent on the presence or absence of BJ1 in N1 soils. In N1 soils, applying biochar at 2 % and 4 % increased the cumulative CO2 emissions by 141.0 % and 166.9 %, respectively, when BJ1 was absent. However, applying biochar did not affect CO2 emissions when BJ1 was present. In addition, the presence of BJ1 generally increased ammonium contents in N0 soils, but decreased nitrate contents in N1 soils relative to the absence of BJ1, which indicates that the combination of biochar and BJ1 is beneficial to play the N fixation function of BJ1 in N0 soils. Our results highlight that biochar addition influences not only soil C mineralization but also soil available N, and the direction and magnitude of these effects are highly dependent on the presence of PGPB and the soil N level.