First field estimation of greenhouse gas release from European soil-dwelling Scarabaeidae larvae targeting the genus Melolontha.

Arthropods are a major soil fauna group, and have the potential to substantially influence the spatial and temporal variability of soil greenhouse gas (GHG) sinks and sources. The overall effect of soil-inhabiting arthropods on soil GHG fluxes still remains poorly quantified since the majority of the available data comes from laboratory experiments, is often controversial, and has been limited to a few species. The main objective of this study was to provide first insights into field-level carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) release of soil-inhabiting larvae of the Scarabaeidae family. Larvae of the genus Melolontha were excavated at various sites in west-central and southern Germany, covering a wide range of different larval developmental stages, larval activity levels, and vegetation types. Excavated larvae were immediately incubated in the field to measure their GHG production. Gaseous carbon release of individual larvae showed a large inter- and intra-site variability which was strongly correlated to larval biomass. This correlation persisted when upscaling individual CO2 and CH4 production to the plot scale. Field release estimates for Melolontha spp. were subsequently upscaled to the European level to derive the first regional GHG release estimates for members of the Scarabaeidae family. Estimates ranged between 10.42 and 409.53 kt CO2 yr-1, and 0.01 and 1.36 kt CH4 yr-1. Larval N2O release was only sporadically observed and not upscaled. For one site, a comparison of field- and laboratory-based GHG production measurements was conducted to assess potential biases introduced by transferring Scarabaeidae larvae to artificial environments. Release strength and variability of captive larvae decreased significantly within two weeks and the correlation between larval biomass and gaseous carbon production disappeared, highlighting the importance of field measurements. Overall, our data show that Scarabaeidae larvae can be significant soil GHG sources and should not be neglected in soil GHG flux research.

<p>Arthropods are a major soil fauna group, and have the potential to substantially influence the spatial and temporal variability of soil greenhouse gas (GHG) sinks and sources. The overall effect of soil-inhabiting arthropods on soil GHG fluxes still remains poorly quantified since the majority of the available data comes from laboratory experiments, is often controversial, and has been limited to a few species. The main objective of this study was to provide first insights into field-level carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) emissions of soil-inhabiting larvae of the Scarabaeidae family. Larvae of the genus <em>Melolontha</em> were excavated at various grassland and forest sites in west-central and southern Germany, covering a wide range of different larval developmental stages, and larval activity levels. Excavated larvae were immediately incubated in the field to measure their GHG emissions. Gaseous carbon emissions of individual larvae showed a large inter- and intra-site variability which was strongly correlated to larval biomass. This correlation persisted when upscaling CO<sub>2</sub> and CH<sub>4 </sub>emissions to the plot scale. Field emission estimates for <em>Melolontha</em> spp. were subsequently upscaled to the European level to derive the first regional GHG emission estimates for members of the Scarabaeidae family. Estimates ranged between 10.42 and 409.53 kt CO<sub>2</sub> yr<sup>-1</sup>, and 0.01 and 1.36 kt CH<sub>4</sub> yr<sup>-1</sup>. Larval N<sub>2</sub>O emissions were only sporadically observed and not upscaled. For one site, a comparison of field- and laboratory-based GHG emission measurements was conducted to assess potential biases introduced by transferring Scarabaeidae larvae to artificial environments. Emission strength and variability of captive larvae decreased significantly within two weeks and the correlation between larval biomass and gaseous carbon emissions disappeared, highlighting the importance of field measurements. Overall, our data show that Scarabaeidae larvae can be significant soil GHG sources and should not be neglected in soil GHG flux research.</p>

BackgroundChanges in soil greenhouse gas (GHG) fluxes caused by nitrogen (N) addition are considered as the key factors contributing to global climate change (global warming and altered precipitation regimes), which in turn alters the feedback between N addition and soil GHG fluxes. However, the effects of N addition on soil GHG emissions under climate change are highly variable and context-dependent, so that further syntheses are required. Here, a meta-analysis of the interactive effects of N addition and climate change (warming and altered precipitation) on the fluxes of three main soil GHGs [carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)] was conducted by synthesizing 2103 observations retrieved from 57 peer-reviewed articles on multiple terrestrial ecosystems globally.ResultsThe interactive effects of N addition and climate change on GHG fluxes were generally additive. The combination of N addition and warming or altered precipitation increased N2O emissions significantly while it had minimal effects on CO2 emissions and CH4 uptake, and the effects on CH4 emissions could not be evaluated. Moreover, the magnitude of the combined effects did not differ significantly from the effects of N addition alone. Apparently, the combined effects on CO2 and CH4 varied among ecosystem types due to differences in soil moisture, which was in contrast to the soil N2O emission responses. The soil GHG flux responses to combined N addition and climate change also varied among different climatic conditions and experimental methods.ConclusionOverall, our findings indicate that the effects of N addition and climate change on soil GHG fluxes were relatively independent, i.e. combined effects of N addition and climate change were equal to or not significantly different from the sum of their respective individual effects. The effects of N addition on soil GHG fluxes influence the feedbacks between climate change and soil GHG fluxes.

Soil greenhouse gas fluxes under elevated nutrient input along an elevation gradient of tropical montane forests in southern Ecuador

Combined effects of glacial retreat and penguin activity on soil greenhouse gas fluxes on South Georgia, sub-Antarctica

<p>The arthropod family Scarabaeidae is estimated to consist of over 30,000 species worldwide, including important pests. Their larvae – commonly known as white grubs – are often part of the soil decomposer community feeding on living plant roots, plant residues as well as faeces. As a result, scarab beetle larvae have the potential to directly and indirectly affect the spatial and temporal variability of soil greenhouse gas (GHG) fluxes, especially through their capability to emit significant amounts of CH<sub>4</sub>. However, due to a lack of field data (Görres & Kammann 2020), little is known about their quantitative impact on soil GHG budgets. We conducted a mesocosm experiment with common cockchafer larvae (<em>Melolontha melolontha</em>) with the twofold aim to better understand their effect on soil CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O fluxes as well as the methodological challenges associated with studying this soil fauna group under field conditions. The experiment was conducted in Germany (temperate zone) over an entire vegetation period in mesocosms with three different vegetation types (grassland, grassland + carrots, and carrots, respectively) and three different larval infestation rates (0, 8, and 16 larvae m<sup>-2</sup>, respectively). Greenhouse gas flux measurements were conducted with the static chamber method on a monthly basis, including the use of isotopic labels to focus especially on gross soil CH<sub>4</sub> fluxes. In this presentation, we will focus on the methodological difficulties encountered during the experiment and the potential of field-based isotope pool dilution techniques for non-invasive studies of scarab beetle larval CH<sub>4</sub> emissions.</p><p>This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 703107.</p><p><strong>Reference</strong></p><p>Görres, C.-M., Kammann, C. (2020). First field estimation of greenhouse gas release from European soil-dwelling Scarabaeidae larvae targeting the genus Melolontha. PLoS ONE 15(8): e0238057, doi 10.1371/journal.pone.0238057.</p>

Abstract. The effect of clear-fell harvesting on soil greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) was assessed in a Sitka spruce forest growing on a peaty gley organo-mineral soil in northern England. Fluxes from the soil and litter layer were measured monthly by the closed chamber method and gas chromatography over 4 years in two mature stands, with one area harvested after the first year. Concurrent measurements of soil temperature and moisture helped to elucidate reasons for the changes in fluxes. In the 3 years after felling, there was a significant increase in the soil temperature, particularly between June and November (3 to 5 ∘C higher), and in soil moisture, which was 62 % higher in the felled area, and these had pronounced effects on the GHG balance in addition to the removal of the trees and their carbon input to the soil. Annual soil CO2 effluxes reduced to almost a third in the first year after felling (a drop from 24.0 to 8.9 t CO2 ha−1 yr−1) and half in the second and third year (mean 11.8 t CO2 ha−1 yr−1) compared to before felling, while those from the unfelled area were little changed. Annual effluxes of N2O more than doubled in the first two years (from 1.0 to 2.3 and 2.5 t CO2e ha−1 yr−1, respectively), although by the third year they were only 20 % higher (1.2 t CO2e ha−1 yr−1). CH4 fluxes changed from a small net uptake of −0.03 t CO2e ha−1 yr−1 before felling to a small efflux increasing over the 3 years to 0.34 t CO2e ha−1 yr−1, presumably because of the wetter soil after felling. Soil CO2 effluxes dominated the annual net GHG emission when the three gases were compared using their global warming potential (GWP), but N2O contributed up to 20 % of this. This study showed fluxes of CO2, CH4, and N2O responded differently to clear-felling due to the significant changes in soil biotic and abiotic factors and showed large variations between years. This demonstrates the need for multi-year measurements of all GHGs to enable a robust estimate of the effect of the clear-fell phase on the GHG balance of managed forests. This is one of very few multi-year monitoring studies to assess the effect of clear-fell harvesting on soil GHG fluxes.

<p>Peatland soils are considered the dominating source of methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) to the atmosphere. However, there are high spatio-temporal uncertainties regarding the soil greenhouse gas (GHG) fluxes due to complex dynamics between the soil chemical, physical and biological variables. Although GHG fluxes from peatland soils are relatively well studied, tree stem fluxes have received far less attention and are often overlooked in GHG models and assessments. Moreover, simultaneous year-long measurements of soil and tree stem CH<sub>4</sub> and N<sub>2</sub>O fluxes in peatland forests are missing, as previous studies have primarily focused on the growing season. We aim to determine the seasonal dynamics of CH<sub>4</sub> and N<sub>2</sub>O fluxes in drained peatland forests, as drainage can lead to release of the large amounts of carbon and nitrogen stored in peat into the atmosphere as GHGs.</p><p>Our research focuses on tree stems and soil GHG fluxes in the Agali Drained Peatland Forest Research Station in Estonia, dominated by Downy Birch (<em>Betula pubescens</em>) and Norway Spruce (<em>Picea abies</em>) trees. During the weekly sampling campaigns (November 2020–December 2021), we used manual static stem chambers to collect gas samples, which were later analysed for CH<sub>4</sub> and N<sub>2</sub>O in the laboratory using Shimadzu GC-2014 gas chromatography. We measured soil CH<sub>4</sub> and N<sub>2</sub>O fluxes using an automated dynamic soil chamber system connected to a Picarro G2508 analyser.</p><p>Preliminary results show that on average, birch stem GHG fluxes were greater than spruce stem fluxes. Birch trees were a net annual source of both CH<sub>4 </sub>(0.38 ± 0.09 µg C m<sup>-2</sup> stem area h<sup>-1</sup>, mean ± SE) and N<sub>2</sub>O (0.94 ± 0.32 µg N m<sup>-2</sup> h<sup>-1</sup>). Spruce trees were a net source of CH<sub>4</sub> (0.08 ± 0.05 µg C m<sup>-2</sup> h<sup>-1</sup>) but a net sink of N<sub>2</sub>O (–0.08 ± 0.02 µg N m<sup>-2</sup> h<sup>-1</sup>). Temporal dynamics of birch stem CH<sub>4</sub> emissions were characterised by significant emission peaks in November and June. During the rest of the year smaller fluxes with fluctuations between emissions and uptake were observed. Spruce stem CH<sub>4</sub> fluxes followed a roughly similar pattern as birch fluxes. However, during the birch emission peak in June, spruce stems showed uptake of CH<sub>4</sub>. Birch stem N<sub>2</sub>O emissions remained very small for most of the year, with increased emissions in autumn months and March. Spruce stem N<sub>2</sub>O fluxes remained very low throughout the year.</p><p>Soils were a net annual sink of CH<sub>4</sub> (–6.44 ± 0.76 µg C m<sup>-2</sup> ground area h<sup>-1</sup>) and source of N<sub>2</sub>O (41.68 ± 3.15 µg N m<sup>-2</sup> h<sup>-1</sup>). CH<sub>4</sub> was taken up by the soil most of the year, however occasional emissions occurred. A substantial increase in CH<sub>4</sub> uptake was observed in June, peaking at –49.53 µg C m<sup>-2</sup> h<sup>-1</sup> at the end of July, and diminishing towards the end of summer. Hot moments – notably higher daily average emissions compared to the period average – characterised the temporal dynamics of soil N<sub>2</sub>O emissions.</p><p>Further results on soil meteorological and biogeochemical properties will help determine the possible drivers of stem and soil fluxes’ dynamics and their origin.</p>

Effects of changes in throughfall on soil GHG fluxes under a mature temperate forest, northeastern China

IntroductionThere is a vast data gap for the national and regional greenhouse gas (GHG) budget from different smallholder land utilization types in Kenya and sub-Saharan Africa (SSA) at large. Quantifying soil GHG, i.e., methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions from smallholder land utilization types, is essential in filling the data gap.MethodsWe quantified soil GHG emissions from different land utilization types in Western Kenya. We conducted a 26-soil GHG sampling campaign from the different land utilization types. The five land utilization types include 1) agroforestry M (agroforestry Markhamia lutea and sorghum), 2) sole sorghum (sorghum monocrop), 3) agroforestry L (Sorghum and Leucaena leucocephala), 4) sole maize (maize monocrop), and 5) grazing land.Results and discussionThe soil GHG fluxes varied across the land utilization types for all three GHGs (p ≤ 0.0001). We observed the lowest CH4 uptake under grazing land (−0.35 kg CH4–C ha−1) and the highest under sole maize (−1.05 kg CH4–C ha−1). We recorded the lowest soil CO2 emissions under sole maize at 6,509.86 kg CO2–Cha−1 and the highest under grazing land at 14,400.75 kg CO2–Cha−1. The results showed the lowest soil N2O fluxes under grazing land at 0.69 kg N2O–N ha−1 and the highest under agroforestry L at 2.48 kg N2O–N ha−1. The main drivers of soil GHG fluxes were soil bulk density, soil organic carbon, soil moisture, clay content, and root production. The yield-scale N2O fluxes ranged from 0.35 g N2O–N kg−1 under sole maize to 4.90 g N2O–N kg−1 grain yields under agroforestry L. Nevertheless, our findings on the influence of land utilization types on soil GHG fluxes and yield-scaled N2O emissions are within previous studies in SSA, including Kenya, thus fundamental in filling the national and regional data of emissions budget. The findings are pivotal to policymakers in developing low-carbon development across land utilization types for smallholders farming systems.

Abstract. A profound understanding of temporal and spatial variabilities of soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes between terrestrial ecosystems and the atmosphere is needed to reliably quantify these fluxes and to develop future mitigation strategies. For managed grassland ecosystems, temporal and spatial variabilities of these three soil greenhouse gas (GHG) fluxes occur due to changes in environmental drivers as well as fertilizer applications, harvests and grazing. To assess how such changes affect soil GHG fluxes at Swiss grassland sites, we studied three sites along an altitudinal gradient that corresponds to a management gradient: from 400 m a.s.l. (intensively managed) to 1000 m a.s.l. (moderately intensive managed) to 2000 m a.s.l. (extensively managed). The alpine grassland was included to study both effects of extensive management on CH4 and N2O fluxes and the different climate regime occurring at this altitude. Temporal and spatial variabilities of soil GHG fluxes and environmental drivers on various timescales were determined along transects of 16 static soil chambers at each site. All three grasslands were N2O sources, with mean annual soil fluxes ranging from 0.15 to 1.28 nmol m−2 s−1. Contrastingly, all sites were weak CH4 sinks, with soil uptake rates ranging from −0.56 to −0.15 nmol m−2 s−1. Mean annual soil and plant respiration losses of CO2, measured with opaque chambers, ranged from 5.2 to 6.5 μmol m−2 s−1. While the environmental drivers and their respective explanatory power for soil N2O emissions differed considerably among the three grasslands (adjusted r2 ranging from 0.19 to 0.42), CH4 and CO2 soil fluxes were much better constrained (adjusted r2 ranging from 0.46 to 0.80) by soil water content and air temperature, respectively. Throughout the year, spatial heterogeneity was particularly high for soil N2O and CH4 fluxes. We found permanent hot spots for soil N2O emissions as well as locations of permanently lower soil CH4 uptake rates at the extensively managed alpine site. Including hot spots was essential to obtain a representative mean soil flux for the respective ecosystem. At the intensively managed grassland, management effects clearly dominated over effects of environmental drivers on soil N2O fluxes. For CO2 and CH4, the importance of management effects did depend on the status of the vegetation (LAI).

Both biochar and nitrogen (N) addition have been proposed for enhancing plant productivity and increasing carbon (C) sequestration. Although numerous studies have been conducted to examine responses of soil greenhouse gas (GHG) fluxes to biochar or N addition, biochar is often co‐applied with N fertilizer and the interactive effects of the two factors still remain unclear. In this study, we performed a meta‐analysis of manipulative experiments with 267 two‐factor observations to quantify the main and interactive effects of biochar and N addition on soil GHG fluxes at a global scale. Our results showed that biochar addition significantly increased soil CO2 emission by 10.1%, but decreased N2O emission by 14.7%. Meanwhile, N addition increased both soil CO2 and N2O emissions by 11.6% and 288%, respectively. The combination of biochar and N addition also exhibited significant positive effect on CO2 (+18.0%) and N2O (+148%) emissions, but there were non‐significant changes in CH4 fluxes. Consequently, antagonistic interaction between biochar and N addition was observed in soil GHG fluxes and their global warming potential (GWP), except for CH4 uptake showing an additive interaction. This synthesis highlights the importance of the interactive effects between biochar and N addition, providing a quantitative basis to develop sustainable strategies toward widespread application of biochar to preserve cropping system and mitigate climate change.

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

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta‐analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation.

ABSTRACTConversion of agricultural fields to bioenergy crops can affect greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Soil GHG emissions were measured seasonally in poplar bioenergy and agricultural fields at three Northwestern US locations. A forest stand was also used at one location for comparison. A portable gas analyzer was used to measure CO2 efflux and CH4 and N2O fluxes were first measured with chambers and later with gradients. Agricultural soil had 17% larger CO2 efflux rates than poplar soil. Chamber fluxes showed no differences in CH4 uptake but did show higher N2O fluxes in poplar than agricultural soil. Gradient CH4 uptake rates were highest in agricultural soil in the summer but showed no N2O flux differences. Forest soils had smaller quarterly CO2 efflux rates than agricultural soils and greater CH4 uptake rates than poplar soils. The largest GHG contributor to soil GHG flux was CO2, with those being ∼1000 times larger than CH4 flux rates and ∼500 times larger than N2O flux rates based on CO2 equivalences. Converting conventional agricultural cropland to poplar bioenergy production does not have adverse effects on soil greenhouse gas flux and these results could be useful for modeling or life cycle analysis of land use conversion.