Greenhouse gas emissions from peatlands under manipulated warming, nitrogen addition, and vegetation composition change: a review and data synthesis

Biochar as soil amendment: Syngas recycling system is essential to create positive carbon credit

Peatlands represent 2.5% of all agricultural land in the EU, yet they account for ~ 25% of agricultural greenhouse gas (GHG) emissions, and ~ 5% of total EU-wide GHG emissions. Several studies have shown that peatland rewetting can reduce, or even reverse, the net GHG emissions from previously drained peatlands. We investigated GHG emissions from 14 different European peatland sites (Germany [6], Poland [4] and Netherlands [4]) across a landuse (3 levels) and water table (2 levels) gradient during a 2 year period (July 2021 – June 2023). GHG flux measurements utilizing closed, non-flow-through, dark, non-steady-state chambers were implemented to estimate ecosystem respiration from the study sites. Ecosystem respiration represents the largest share of carbon export to the atmosphere from terrestrial ecosystems. Within the study, landuse gradient was represented by the level of paludiculture (harvest frequency/ soil nitrogen levels), and water table level indicated by Typha- and Carex- dominated vegetation. Initial study results indicate that overall, CO2 fluxes varied across seasons (ANOVA, p<0.001, n = 1738, F = 14.08), with the highest fluxes occurring in summer (0.402 ± 0.342 g CO2 m-2h-1), and lowest in winter (0.233 ± 0.368 g CO2 m-2h-1). Similarly, CH4 fluxes varied seasonally, with the highest CH4 fluxes in summer (6.95 ± 8.07 mg CH4 m-2h-1) and lowest in winter (1.98 ± 4.07 mg CH4 m-2h-1). Average CO2 fluxes decreased with the increasing level of paludiculture intensity for both Typha and Carex dominated sites, while CH4 fluxes typically increased with increasing harvest frequency/ soil nitrogen levels. While CO2 and CH4 fluxes were generally higher in the early morning (as compared to afternoons), particularly during summer and autumn, we could not show an overall significant diurnal difference in GHG fluxes. Seasonal variability in CO2 and CH4 was likely an indicator of the effect of temperature and water table level on GHG fluxes. GHG fluxes at the Typha dominated sites were consistently higher than those of complimentary Carex dominated sites for each landuse class, highlighting the importance of water table and vegetation species on GHG emissions. This research was conducted as part of the Peatland Rewetting In Nitrogen-Contaminated Environments: Synergies and trade-offs between biodiversity, climate, water quality & Society (PRINCESS) project, investigating rewetting of drained, nitrogen contaminated peatlands and their potential role in reducing EU-wide greenhouse gas emissions and improving wetland biodiversity.

The System of Rice Intensification (SRI) is known as a climate-smart agricultural practice that increases rice production by changing the management of plants, soil, water, and nutrients. SRI water management relies on intermittent irrigation rather than on the continuous flooding of conventionally managed rice production. Different water table levels affect the soil conditions which contribute to different fluxes of greenhouse gas (GHG) emissions. This study estimated the impact on global warming potential (GWP) of GHG emissions from rice paddies when an SRI crop is managed with different water table levels. In this study, CO2 equivalence was assessed using a Simple Greenhouse Gas model, and an artificial neural network model for assessing CH4 and N2O. SRI paddy rice was grown in experimental pots under varying water table treatments, with the water table controlled by using Mariotte tubes set at + 2, 0, − 3, − 5, − 7, and − 12 cm from the soil surface. GHG emissions, which could be monitored more closely in pot trials than in fields, are a composite of the plants’ respiration, soil respiration (which is a result primarily of microbial activity), and the respiration that results from root exudates. With SRI practices, rice paddies can serve as a sink rather than a source for CH4 as seen from the negative values for CH4 emissions at all water table treatments. While there were N2O emissions with SRI practice, they were much less in terms of CO2 equivalence than the GWP reduction achieved by reducing CH4. Overall, under the experimental conditions the best water table level for SRI cultivation, with the most rice produced relative to GHG emissions, was − 5 cm from the soil surface. For each kg of grain produced, there were 0.80 kg CO2 eq of GHG emissions. By comparison, a normally flooded paddy field with usual crop management methods emits 1.97 kg CO2 eq per kg of grain produced, almost 150% more. This finding that a water table of − 5 cm is optimal will not necessarily apply for all field conditions, but the research addresses the desirability of seeking to optimize between GHG reductions and increased yield when growing paddy rice, and of developing appropriate methodology for achieving this composite objective.

Understory management and fertilization affected soil greenhouse gas emissions and labile organic carbon pools in a Chinese chestnut plantation

Greenhouse gas fluxes under drought and nitrogen addition in a Southern California grassland

Forests can play a key role in the mitigation of climate change, although there have been limited regional scale assessments that account for variations in soil type and tree species. Most of the focus has been on their ability to sequester atmospheric CO2, while there is less information on the two other major greenhouse gases (GHGs), N2O and CH4. We examined the GHG budgets of ten forest soils in Poland, considering all three major GHGs, where no previous long-term measurements had been made, which encompassed different tree species, stand age, and contrasting edaphic conditions. In addition to the quantification and assessment of seasonal variability in the major soil GHG fluxes over two years, the aims of the present study were (i) the identification of the main drivers of the soil-based GHG fluxes, (ii) the determination of the contribution of each gas to the Global Warming Potential (GWP), and (iii) to assess the mitigation potential of these fluxes over different forest systems. All the forest soils were sources of CO2 and N2O and sinks for atmospheric CH4 with pronounced seasonal variations in CO2 and CH4 driven by soil moisture and temperature. The soils showed significant differences in annual GHG fluxes, with average values of 16.7 Mg CO2 ha−1, − 3.51 kg CH4 ha−1, and 0.95 kg N2O ha−1. The annual total GWP ranged from 13.1 to 22.0 Mg CO2 eq ha−1 with CO2 making the highest contribution, and forest-specific CH4 uptake resulting in a reduction in GWP, ranging from − 0.08% (in the youngest forest) to -0.97% (in the oldest forest). Mixed forests showed the greatest potential for climate change mitigation, with the highest soil C sequestration, and the lowest GWP values when compared to sites with monocultures. The results suggest that a mixture of tree species could eventually be incorporated into management plans to increase the effectiveness of forests in climate change mitigation.

Freshwater wetlands can contribute significantly to the global carbon budget as a net source or sink of the major greenhouse gas (GHG) fluxes such as carbon dioxide (FCO2) and methane (FCH4). The amount of GHG fluxes in the freshwater wetlands is highly variable and depends on a range of environmental drivers. These wetlands are commonly hypothesized to be net sinks (i.e., burial) of FCO2 and net sources (emission) of FCH4 at the monthly to annual scales. Understanding the environmental controls on the wetland GHG fluxes is essential for an accurate estimation of the global GHG budget, which is often used as a pivotal measure to reduce GHG emissions and enhance carbon sequestration. In this study, we analyzed FLUXNET data from 38 freshwater wetlands located across the globe to investigate the relationships of monthly-scale GHG fluxes with various climatic and ecohydrological drivers. Data analytics with multivariate pattern recognition techniques—including principal component analysis, factor analysis, and partial least squares regression— were performed to identify and quantify the dominant controls of wetland FCO2 and FCH4 fluxes. The environmental controls on the GHG fluxes in freshwater wetlands were found to highly vary based on the climatic zones. In the tropical (i.e., mega thermal) zone, the GHG fluxes were overall primarily controlled by photosynthetically active radiation (PAR), soil temperature (TS), wind speed (WS), friction velocity (USTAR), and vapor pressure deficit (VPD). However, the latent heat flux (LE) and VPD, alongside PAR, TS, and USTAR, exhibited the dominant controls on the GHG fluxes in the dry (or arid) zone wetlands. Both GHG fluxes in wetlands of the temperate (or mesothermal) zone were mainly controlled by water table depth (WL), TS, and LE. Surprisingly, PAR did not appear to be a strong driver of the monthly averaged fluxes in the temperate wetlands. In contrast, PAR, LE, TS, WS, and USTAR were the primary controlling factors of the GHG fluxes in wetlands representing continental (or microthermal) climates. However, in wetlands of the polar (alpine) region, sensible heat flux (H) had a strong linkage with the GHG fluxes, alongside the controls of PAR, TS, WS, VPD and USTAR. These findings and new knowledge can help inform wetland management and conservation strategies, particularly in the context of climate and land cover changes. Effective management and conservation of wetlands can help reduce GHG emissions, thereby contributing to the mitigation efforts on global warming.

Response of soil greenhouse gas fluxes to warming: A global meta‐analysis of field studies

Comprehensive soil greenhouse gas flux dataset from a temperate old-growth forest: Effects of decade-long nitrogen addition and biological factor manipulation.

Altered precipitation rather than warming and defoliation regulate short-term soil carbon and nitrogen fluxes in a northern temperate grassland

Reindeer (Rangifer tarandus L.) is considered to be an important mammalian herbivore, strongly influencing Arctic lichen‐dominated ecosystems. There is no wide knowledge about the effect of reindeer on greenhouse gas (GHG) fluxes in northern boreal forests. Ground vegetation plays an important role in absorbing nitrogen (N) and carbon dioxide (CO2) from the atmosphere. Lately, it has also been found to be a significant source of nitrous oxide (N2O) and a small source of methane (CH4). We investigated the influence of reindeer grazing on field layer GHG (CO2, CH4, and N2O) fluxes, ground vegetation coverage and biomass, and soil physical properties (temperature and moisture) in a northern boreal forest. At our study site, the reindeer‐induced replacement of lichen by mosses had contrasting effects on the GHG fluxes originating from the field layer. Field layer CO2 efflux was significantly higher in grazed areas. The field layer was a CH4 sink in all areas, but grazed areas absorbed more CH4 compared to non‐grazed areas. Although total N2O fluxes remained around 0 in grazed areas, a small N2O sink occurred in non‐grazed areas with lower moss biomass. Our results indicated that grazing by reindeer in northern boreal forests affects GHG fluxes from the forest field layer both positively and negatively, and these emissions largely depend on grazing‐induced changes in vegetation composition.

An incubation study of temperature sensitivity of greenhouse gas fluxes in three land-cover types near Sydney, Australia

<p>Biochar is a carbon-rich black stable solid substance that when utilized as soil amendment can effectively mitigate greenhouse gas (GHG) emission. However, during the pyrolysis process of organic feedstock (i.e. manure) greenhouse gases are released as the feedstock undergo thermochemical degradation. Many studies were reported with regards to the effectiveness of biochar to mitigate greenhouse gas emission and to maintain soil quality via carbon sequestration. However, no clear investigation was done regarding biochar utilization on reducing GHG emission in an integrated perspective that starts from pyrolysis (production) to field application (utilization). To evaluate the integrated influence of biochar utilization on the overall Global Warming Potential (GWP) and (Greenhouse Gas Intensity) GHGI at different temperature, the fluxes of GHGs during feedstock pyrolysis to soil application were calculated. The key components include GHGs released during production processes and biogenic GHG emissions taking place in the soil via short-term incubation experiment in lowland and upland condition treated with biochar pyrolyzed at different temperature. Highest pyrolysis temperature of 700<sup>o</sup>C emitted 6.92 Mg CO<sub>2</sub>-eq ton<sup>-1</sup> biochar, wherein 8.7% and 91.2% was contributed by Carbon dioxide (CO<sub>2</sub>) and Methane (CH<sub>4</sub>) effluxes, respectively, during pyrolysis. This GHG emission during pyrolysis at 700<sup>o</sup>C was 5.6, 2.2, and 1.5 times higher than at 400<sup>o</sup>C, 500<sup>o</sup>C and 600<sup>o</sup>C, respectively. Meanwhile, biochar produced at lowest temperature (Biochar400) when utilized as soil amendment emitted 43.4 and 38.2 Mg CO<sub>2</sub>-eq ha<sup>-1</sup> in lowland and upland condition, respectively. In addition, this emission value under lowland (and upland) condition was 1.38 (1.36), 1.51 (1.56) and 1.86 (1.91) times higher than Biochar500, Biochar600 and Biochar700, respectively. Combining the GWP during the production and the utilization processes in lowland and upland condition reveal that at 400<sup>o</sup>C emanates the lowest overall GWP of 93.3 and 88.1 Mg CO<sub>2</sub>-eq ha<sup>-1</sup>, respectively.  Moreover, under lowland (and upland) condition, overall GWP at 400<sup>o</sup>C was noted to be 65.7% (71.7%), 131.6% (140.4%) and 221.9% (237.1%), lower than at 500<sup>o</sup>C, 600<sup>o</sup>C and 700<sup>o</sup>C, respectively. In conclusion, the use of lower temperature during biomass pyrolysis and utilization of its derived biochar could be a practical approach to mitigate GHG emissions.</p><p> </p><p>Keywords: Biochar, Pyrolysis, Greenhouse gas, Methane, Global warming potential, Greenhouse gas intensity</p>

Soil nutrient management is a key component contributing to the greenhouse gas (GHG) flux and mitigation potential of agricultural production systems. However, the effect of soil nutrient management practices on GHG flux and global warming potential (GWP) is less understood in agricultural soils of India. The present study was conducted to compare three nutrient management systems practiced for nine consecutive years in a soybean-wheat cropping system in the Vertisols of India, in terms of GHG flux and GWP. The treatments were composed of 100% organic (ONM), 100% inorganic (NPK), and integrated nutrient management (INM) with 50% organic+50% inorganic inputs. The gas samples for GHGs (CO2, CH4, and N2O) were collected by static chamber method at about 15-day interval during 2012-13 growing season. The change in soil organic carbon (SOC) content was estimated in terms of the changes in SOC stock in the 0-15cm soil over the 9-year period covering 2004 to 2013. There was a net uptake of CH4 in all the treatments in both soybean and wheat crop seasons. The cumulative N2O and CO2 emissions were in the order of INM>ONM>NPK with significant difference between treatments (p<0.05) in both the crop seasons. The annual GWP, expressed in terms of CH4 and N2O emission, also followed the same trend and was estimated to be 1126, 1002, and 896kg CO2 eqha-1year-1 under INM, ONM, and NPK treatments, respectively. However, the change in SOC stock was significantly higher under ONM (1250kgha-1year-1) followed by INM (417kgha-1year-1) and least under NPK (198kgha-1year-1) treatment. The wheat equivalent yield was similar under ONM and INM treatments and was significantly lower under NPK treatment. Thus, the GWP per unit grain yield was lower under ONM followed by NPK and INM treatments and varied from 250, 261, and 307kg CO2 eqMg-1 grain yield under ONM, NPK, and INM treatments, respectively.

Grassland ecosystems play an essential role in climate regulation through carbon (C) storage in plant and soil. But, anthropogenic practices such as livestock grazing, grazing related excreta nitrogen (N) deposition, and manure/fertilizer N application have the potential to reduce the effectiveness of grassland C sink through increased nitrous oxide (N2O) and methane (CH4) emissions. Although the effect of anthropogenic activities on net greenhouse gas (GHG) fluxes in grassland ecosystems have been investigated at local to regional scales, estimates of net GHG balance at the global scale remains uncertain. With the data-model framework integrating empirical estimates of livestock CH4 emissions with process-based modeling estimates of land CO2, N2O and CH4 fluxes, we examined the overall global warming potential (GWP) of grassland ecosystems during 1961–2010. We then quantified the grassland-specific and regional variations to identify hotspots of GHG fluxes. Our results show that, over a 100-year time horizon, grassland ecosystems sequestered a cumulative total of 113.9 Pg CO2-eq in plant and soil, but then released 91.9 Pg CO2-eq to the atmosphere, offsetting 81% of the net CO2 sink. We also found large grassland-specific variations in net GHG fluxes, with pasturelands acting as a small GHG source of 1.52 ± 143 Tg CO2-eq yr−1 (mean ± 1.0 s.d.) and rangelands a strong GHG sink (−442 ± 266 Tg CO2-eq yr−1) during 1961–2010. Regionally, Europe acted as a GHG source of 23 ± 10 Tg CO2-eq yr−1, while other regions (i.e. Africa, Southern Asia) were strong GHG sinks during 2001–2010. Our study highlights the importance of considering regional and grassland-specific differences in GHG fluxes for guiding future management and climate mitigation strategies in global grasslands.