Soil Greenhouse Gas Research Articles

Soil greenhouse gas emissions and grazing management in northern temperate grasslands

Adaptive multi-paddock (AMP) grazing, a grazing system in which individual paddocks are grazed for a short duration at a high stock density and followed by a long rest period, is claimed to be an effective tool to sustainably manage and improve grasslands and enhance their ecosystem services. However, whether AMP grazing is superior to conventional grazing (n-AMP) in reducing soil greenhouse gas (GHG) emissions is unclear. Here, we measured CO2, CH4, and N2O fluxes between August 2017 and August 2019 in 12 pairs of AMP vs. n-AMP ranches distributed across an agro-climatic gradient in Alberta, Canada. We found that field GHG fluxes did not differ between AMP and n-AMP grazing systems, but instead were regulated by specific management attributes, environmental conditions, and soil properties, including cattle stocking rate, cultivation history, soil moisture content, and soil bulk density. Specifically, we found that seasonal mean CO2 emissions increased with increasing cattle stocking rates, while CH4 uptake was lower in grasslands with a history of cultivation. Seasonal mean CO2 emissions increased while CH4 uptake decreased with increasing soil moisture content. In addition, CH4 uptake decreased with increasing soil bulk density. Observed N2O emissions were poorly predicted by the management, environmental conditions, and soil properties investigated in our study. We conclude that AMP grazing does not have an advantage over n-AMP grazing in reducing GHG fluxes from grasslands. Future efforts to develop optimal management strategies (e.g., the use of sustainable stocking rates and avoided cultivation) that reduce GHG emissions should also consider the environmental conditions and soil properties unique to every grassland ecosystem.

Effects of experimental fire in combination with climate warming on greenhouse gas fluxes in Arctic tundra soils

The frequency and severity of fire is increasing in Arctic tundra regions with climate change. Here we investigated effects of experimental low-intensity fire and shrub cutting, in combination with warming, on soil biogeochemical cycles and post-fire greenhouse gas (GHG) emissions in a dry heath tundra, West Greenland. We performed in vitro incubation experiments based on soil samples collected for up to two years after the fire. We observed tendency for increased soil nitrate (14-fold) and significant increases in soil ammonium and phosphate (four-fold and five-fold, respectively) two years after the fire, but no effects of shrub cutting on these compounds. Thus, changes appear to be largely due to fire effects rather than indirect effects by vegetation destruction. Two years after fire, nitrous oxide (N2O) and carbon dioxide (CO2) production was significantly increased (three-fold and 32% higher, respectively), in burned than unburned soils, while methane (CH4) uptake remained unchanged. This stimulated N2O and CO2 production by the fire, however, was only apparent under conditions when soil was at maximum water holding capacity, suggesting that fire effects can be masked under dry conditions in this tundra ecosystem. There were positive effects by modest 2.5 °C warming on CO2 production in control but not in burned soils, suggesting that fire may decrease the temperature response in soil respiration. Methane uptake was neither altered by the modest warming in shrub-cut nor in burned soils after two years, suggesting that the removal of vegetation may play a key role in controlling future temperature response of CH4 oxidation. Altogether, our results show that post-fire tundra soils have the potential to enhance soil GHG emissions (e.g. N2O and CO2) especially during episodes with wet soil conditions. On the other hand, the lack of warming responses in post-fire soil respiration may weaken this positive feedback to climate change.

Responses of greenhouse gas emissions to different straw management methods with the same amount of carbon input in cotton field

Recycling crop straw to cropland can improve soil fertility, increase crop yield, and enhance soil carbon (C) sequestration, but also increase the risk of soil greenhouse gas (GHG) emissions. However, the differences in GHG emissions among different straw management methods are not well understood. Here, we investigated the responses of GHG emissions and their driving factors to the application of straw (S, 5.0 t ha−1), straw plus microbial inoculant (SI, 5.0 t ha−1), straw mulching (SM, 5.0 t ha−1), straw-biochar (SB, 3.5 t ha−1), and no straw or straw-biochar (CK) based on an equal amount of C input in a cotton field in Yancheng city, Jiangsu province, China from 2017 to 2018. Our results showed that the carbon dioxide (CO2) emissions from soil heterotrophic respiration were decreased markedly under SB, but increased markedly under SI and S. The response of soil methane (CH4) emissions to all treatments was similar to the CO2 emissions. Soil nitrous oxide (N2O) emissions were consistently decreased under SB, SI, S and SM, ranking as CK > SM > S>SI > SB. Compared with CK, SI and S significantly increased the global warming potential (GWP), whereas SB significantly decreased GWP by 17.9 %–19.8 %. Lint yield of cotton was highest in SB, followed by SI, S and SM, and lowest in CK. Consequently, SI, S and SM had no significant effects on the greenhouse gas intensity (GHGI), but SB significantly decreased GHGI by 28.4 %–35.7 %. In conclusion, straw-biochar application is an effective option for mitigating global warming and sustaining crop productivity.

Conversion of marginal land into switchgrass conditionally accrues soil carbon but reduces methane consumption

Switchgrass is a deep-rooted perennial native to the US prairies and an attractive feedstock for bioenergy production; when cultivated on marginal soils it can provide a potential mechanism to sequester and accumulate soil carbon (C). However, the impacts of switchgrass establishment on soil biotic/abiotic properties are poorly understood. Additionally, few studies have reported the effects of switchgrass cultivation on marginal lands that have low soil nutrient quality (N/P) or in areas that have experienced high rates of soil erosion. Here, we report a comparative analyses of soil greenhouse gases (GHG), soil chemistry, and microbial communities in two contrasting soil types (with or without switchgrass) over 17 months (1428 soil samples). These soils are highly eroded, ‘Dust Bowl’ remnant field sites in southern Oklahoma, USA. Our results revealed that soil C significantly increased at the sandy-loam (SL) site, but not at the clay-loam (CL) site. Significantly higher CO2 flux was observed from the CL switchgrass site, along with reduced microbial diversity (both alpha and beta). Strikingly, methane (CH4) consumption was significantly reduced by an estimated 39 and 47% at the SL and CL switchgrass sites, respectively. Together, our results suggest that soil C stocks and GHG fluxes are distinctly different at highly degraded sites when switchgrass has been cultivated, implying that carbon balance considerations should be accounted for to fully evaluate the sustainability of deep-rooted perennial grass cultivation in marginal lands.

Contradictory Results of Soil Greenhouse Gas Emissions as Affected by Biochar Application: Special Focus on Alkaline Soils

Contradictory Results of Soil Greenhouse Gas Emissions as Affected by Biochar Application: Special Focus on Alkaline Soils

Responses of Low-Cost Input Combinations on the Microbial Structure of the Maize Rhizosphere for Greenhouse Gas Mitigation and Plant Biomass Production.

The microbial composition of the rhizosphere and greenhouse gas (GHG) emissions under the most common input combinations in maize (Zea mays L.) cultivated in Brazil have not been characterized yet. In this study, we evaluated the influence of maize stover coverage (S), urea-topdressing fertilization (F), and the microbial inoculant Azospirillum brasilense (I) on soil GHG emissions and rhizosphere microbial communities during maize development. We conducted a greenhouse experiment and measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes from soil cultivated with maize plants under factorial combinations of the inputs and a control treatment (F, I, S, FI, FS, IS, FIS, and control). Plant biomass was evaluated, and rhizosphere soil samples were collected at V5 and V15 stages and DNA was extracted. The abundance of functional genes (mcrA, pmoA, nifH, and nosZ) was determined by quantitative PCR (qPCR) and the structure of the microbial community was assessed through 16S rRNA amplicon sequencing. Our results corroborate with previous studies which used fewer input combinations and revealed different responses for the following three inputs: F increased N2O emissions around 1 week after application; I tended to reduce CH4 and CO2 emissions, acting as a plant growth stimulator through phytohormones; S showed an increment for CO2 emissions by increasing carbon-use efficiency. IS and FIS treatments presented significant gains in biomass that could be related to Actinobacteria (19.0%) and Bacilli (10.0%) in IS, and Bacilli (9.7%) in FIS, which are the microbial taxa commonly associated with lignocellulose degradation. Comparing all factors, the IS (inoculant + maize stover) treatment was considered the best option for plant biomass production and GHG mitigation since FIS provides small gains toward the management effort of F application.

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

Climate change scenarios predict a change in the rainfall regimes for this current century, which has different impacts on soil greenhouse gas (GHG) fluxes. However, how changes in annual rainfall affect annual GHG fluxes of forest soils remain unknown. A six-year field experiment with −25% and −50% throughfall (TF) and +25% TF manipulation was performed to explore the mechanisms involving GHG fluxes under a mature temperate forest, northeastern China and to work out whether the TF effect sizes on annual soil GHG fluxes vary with dry and wet years. The results showed that both −25% TF and −50% TF treatments depressed annual soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions but increased annual soil methane (CH4) uptake. A contrary pattern of annual soil GHG fluxes was observed in the +25% TF treatment. When annual TF input was decreased by 100 mm, annual soil N2O and CO2 emissions were decreased by 18.1 ± 3.1 mg N m−2 and by 39.4 ± 6.1 g C m−2 during the growing season, respectively, and annual soil CH4 uptake was increased by 11.5 ± 3.4 mg C m−2. Both −25% TF and −50% TF treatments reduced annual soil dissolved organic C (DOC) leaching by 29.3% and 45.6% and dissolved total N (DN) leaching by 30.8% and 39.6%, respectively. Contrary to annual soil N2O and CO2 emissions, annual soil CH4 uptake during the growing season significantly decreased with an increase in the annual leaching fluxes of soil DOC, inorganic N, and DN. Besides soil moisture and temperature and pH, soil GHG fluxes under manipulating TF condition were regulated by soil labile C and N status. Our findings indicated that the TF effect sizes on both annual GHG fluxes and net annual GHG balance (GWP) of forest soils varied with dry and wet years in northeastern China. The results highlight the importance of altered annual rainfall in regulating annual soil GHG fluxes and the GWP in temperate forests under global climate change.

Are CH4, CO2, and N2O Emissions from Soil Affected by the Sources and Doses of N in Warm-Season Pasture?

The intensification of pasture production has increased the use of N fertilizers—a practice that can alter soil greenhouse gas (GHG) fluxes. The objective of the present study was to evaluate the fluxes of CH4, CO2, and N2O in the soil of Urochloa brizantha ‘Marandu’ pastures fertilized with different sources and doses of N. Two field experiments were conducted to evaluate GHG fluxes following N fertilization with urea, ammonium nitrate, and ammonium sulfate at doses of 0, 90, 180, and 270 kg N ha−1. GHG fluxes were quantified using the static chamber technique and gas chromatography. In both experiments, the sources and doses of N did not significantly affect cumulative GHG emissions, while N fertilization significantly affected cumulative N2O and CO2 emissions compared to the control treatment. The N2O emission factor following fertilization with urea, ammonium nitrate, and ammonium sulfate was lower than the United Nations’ Intergovernmental Panel on Climate Change standard (0.35%, 0.24%, and 0.21%, respectively, with fractionation fertilization and 1.00%, 0.83%, and 1.03%, respectively, with single fertilization). These findings are important for integrating national inventories and improving GHG estimation in tropical regions.

Soil greenhouse gas emissions from a sisal chronosequence in Kenya

Sisal (Agave sisalana) is a climate-resilient crop grown on large-scale farms in semi-arid areas. However, no studies have investigated soil greenhouse gas (GHGs: CO2, N2O and CH4) fluxes from these plantations and how they relate to other land cover types. We examined GHG fluxes (Fs) in a sisal chronosequence at Teita Sisal Estate in southern Kenya. The effects of stand age on Fs were examined using static GHG chambers and gas chromatography for a period of one year in seven stands: young stands aged 1–3 years, mature stands aged 7–8 years, and old stands aged 13–14 years. Adjacent bushland served as a control site representing the surrounding land use type. Mean CO₂ fluxes were highest in the oldest stand (56 ± 3 mg C m-2 h-1) and lowest in the 8-year old stand (38 ± 3 mg C m-2 h-1), which we attribute to difference in root respiration between the stand. All stands had 13–28% higher CO₂ fluxes than bushland (32 ± 3 mg C m-2 h-1). CO2 fluxes in the wet season were about 70% higher than dry season across all sites. They were influenced by soil water content (WS) and vegetation phenology. Mean N2O fluxes were very low (<5 µg N m-2 h-1) in all sites due to low soil nitrogen (N) content. About 89% of CH4 fluxes were below the detection limit (LOD ± 0.02 mg C m-2 h-1). Our results imply that sisal plantations have higher soil CO2 emissions than the surrounding land use type, and the seasonal emissions were largely driven by WS and the vegetation status. Methane and nitrous oxide are of minor importance. Thus, soil GHG fluxes from sisal plantations are a minor contributor to agricultural GHG emissions in Kenya.

Effects of green manure return regimes on soil greenhouse gas emissions

Effects of green manure return regimes on soil greenhouse gas emissions

Influence of land-use change and season on soil greenhouse gas emissions from a tropical wetland: A stepwise explorative assessment

Tropical wetlands are important climate regulators. However, their climate regulating function is at risk by land-use conversion for agricultural purposes. In sub-Saharan Africa, studies investigating the effect of land-use change in wetlands and associated soil greenhouse gas (GHG) emissions remain limited. Moreover, the influence of season in GHG emissions with land-use change has hardly been studied. Therefore, we investigated methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions from a Kenyan wetland and adjacent areas converted to farmland during the dry and rainy seasons. Moreover, we assessed which soil parameters drive the variations in GHG emissions. The GHG samples were collected by the static chamber method and analyzed by gas chromatography. For data analysis, we employed an explorative-statistical approach to explain the emission rates' variation and determine which parameters influence the GHG emissions, both as main and interaction effects. The results showed that regardless of the season, there were CH4 emissions (>0.50 mg m−2 h−1) from the wetland when soil organic carbon content was high and uptake (<0.001 mg m−2 h−1) when both soil organic carbon content and soil moisture were low. In the farmland, there was CH4 uptake when soil nitrate‑nitrogen content was high. CO2 emissions did not vary significantly between the land-use types. Instead, emission rates were primarily governed by season. The highest emissions (>175 mg m−2 h−1) during the dry season were attributed to high soil organic carbon content. During the rainy season, emissions hardly exceeded 175 mg m−2 h−1. Regarding N2O, we detected the highest emissions (>5 μg m−2 h−1) from the farmland during the dry season. Overall, this study shows that wetland conversion to farmland encourages CH4 uptake regardless of the season and increases N2O emissions during the dry season. Based on the respective GHG global warming potential, these patterns may pose an increased environmental threat.

Management intensive grazing on New England dairy farms enhances soil nitrogen stocks and elevates soil nitrous oxide emissions without increasing soil carbon

Management intensive grazing (MIG), also known as rotational grazing or multi-paddock grazing, is purported to sequester carbon (C) in soils compared to other agricultural management systems. Prior research examining the potential for MIG to enhance soil C has been inconclusive, and past investigations have not addressed whether higher nitrous oxide (N2O) emissions may accompany increases in soil C stocks. Here we examined linkages among MIG, soil C accumulation, and N2O emissions in cool-season, organic pastures of the northeastern United States. We found that pastures under MIG increased soil C concentrations by 11% from 0–15 cm depth but that soil C stocks at all sampled depths did not differ between hayed and grazed fields. We observed a divergent response in soil N to MIG, where both N concentrations and stocks significantly increased and the soil C:N ratio significantly decreased in rotationally grazed pastures. Our results also demonstrated that during the second year of the study, N2O emissions were on average 33% higher in grazed fields and compared to hayed fields. These elevated N2O fluxes in MIG fields may have offset any soil C gains achieved under MIG, as demonstrated by similar climate forcing values (as CO2-equivalents) for hayed and grazed pastures over a 100-year time horizon. The significant variation we detected among farms in soil C and N stocks, soil microbial activity, plant biomass production, and soil greenhouse gas emissions demonstrates that MIG does not have uniform effects across the landscape. Overall, our study demonstrates that care should be taken when promoting management practices that may have unintended climate consequences.

Drivers of greenhouse gas emissions from standing dead trees in ghost forests

Coastal freshwater forested wetlands are rapidly transitioning from forest to marsh, leaving behind many standing dead trees (snags) in areas often called ‘ghost forests’. Snags can act as conduits for soil produced greenhouse gases (GHG) and can also be sources as they decompose. Thus, snags have the potential to contribute GHGs to the atmosphere, but emissions are not well understood. We assessed GHG emissions (carbon dioxide—CO2, methane—CH4, and nitrous oxide—N2O) from snags and soils in five ghost forests along a salinity gradient on the coast of North Carolina, USA. Mean (± SE) soil GHG fluxes (416 ± 44 mg CO2 m−2 h−1, 5.9 ± 1.9 mg CH4 m−2 h−1, and 0.1 ± 0.06 mg N2O m−2 h−1) were ~ 4 times greater than mean snag GHGs (116 ± 15 mg CO2 m−2 h−1, 0.3 ± 0.09 mg CH4 m−2 h−1, and 0.04 ± 0.009 mg N2O m−2 h−1). Hydrological conditions and salinity influenced soil GHG fluxes between the two field campaigns, but snags were less predictable and more variable. Snag and soil CO2/N2O fluxes were influenced by similar environmental parameters. The drivers for soil and snag CH4 however, were often not the same and at times oppositely correlated. Our results illustrate the need to further research into the drivers and importance of GHG emissions from snags, and the need to include tree stems into ecosystem GHG research.

Parameterization, calibration and validation of the DNDC model for carbon dioxide, nitrous oxide and maize crop performance estimation in East Africa

Dynamic biogeochemical models are crucial tools for simulating the complex interaction between soils, climate and plants; thus the need for improving understanding of nutrient cycling and reduction of greenhouse gases (GHG) from the environment. This study aimed to calibrate and validate the DeNitrification-DeComposition (DNDC) model for soil moisture, temperature, respiration, nitrous oxide and maize crop growth simulation in drier sub-humid parts of the central highlands of Kenya. We measured soil GHG fluxes from a maize field under four different soil fertility management practices for one year using static chambers and gas chromatography. Using experimental data collected from four management practices during GHG sampling period, we parameterized the DNDC model. The results indicate that the DNDC model simulates daily and annual soil moisture, soil temperature, soil respiration (CO2), nitrous oxide (N2O), N2O yield-scaled emissions (YSE), N2O emission factors (EFs) and maize crop growth with a high degree of fitness. However, the DNDC simulations slightly underestimated soil temperature (2–6%), crop growth (2–45%) and N2O emissions (5–23%). The simulation overestimated soil moisture (9–17%) and CO2 emissions (3–10%). It however, perfectly simulated YSE and EFs. Compared to the observed/measured annual GHG trends, the simulation results were relatively good, with an almost perfect fitting of emission peaks during soil rewetting at the onset of rains, coinciding with soil fertilisation. These findings provide reliable information in selecting best farm management practice, which simultaneously improves agricultural productivity and reduces GHG emissions, thus permitting climate-smart agriculture. The good DNDC simulated YSE and EFs values (Tier III) provide cheaper and reliable ways of filling the huge GHG data gap, reducing uncertainties in national GHG inventories and result to efficient targeting of mitigation measures in sub-Saharan Africa.

Does Biochar Influence Soil CO2 Emission Four Years After Its Application to Soil?

Abstract Biochar application into soil has potential as a means for reducing soil greenhouse gas emissions and climate mitigation strategy. In this study, we evaluated the impact of two doses of biochar (10 and 20 t.ha−1) applied in 2014, combined with three fertilization levels (N0, N1, N2) on carbon dioxide (CO2) in field conditions during the growing season (April – October) in 2018. The field site is located in the Nitra region of Slovakia – Malanta. The soil in the field was classified as a silt loam Haplic Luvisol. There was not found any statistically significant (P &lt;0.05) decreasing effect of biochar with or without N-fertilizer after four years of its application on average daily and cumulative CO2 emissions, while the CO2 emissions increased with additional N-fertilizer. Biochar decreased (insignificantly) the daily and cumulative CO2 emissions only in the treatments without N-fertilization and in the treatment fertilized with higher level of biochar application (20 t.ha−1) and N-fertilizer (80 kg.N.ha−1). According to these results it can be concluded that the biochar applied to soil is not able to reduce CO2 emissions after four years of its application when it is combined with usual agriculture practices which include N-fertilization.

Changes in the Soil–Plant–Water System Due to Biochar Amendment

The aim of this study was to do a complex examination of the soil–plant–water system and soil greenhouse gas emissions when biochar is applied to soil planted with sweet corn (Zea mays L. var. saccharata). The study covers two consecutive vegetation periods. We investigated (i) the changes in plant growth, (ii) soil water and temperature at different depths, (iii) greenhouse gas (GHG) emissions (CO2 and N2O) after biochar application, and (iv) the soil water, chemistry, and plant interactions. We used discrete measurements for plant growth, biomass production, and soil chemistry, while continuously monitoring the soil water content and temperature, and the state of plant health (i.e., using spectral reflectance sensors). Plant response in the control plot showed higher values of normalized difference vegetation index (NDVI; 0.3%) and lower values for photochemical reflectance index (PRI) and fraction of absorbed photosynthetically active radiation (fAPAR) by 26.8% and 2.24%, respectively, than for biochar treatments. We found significant negative correlations between fAPAR and soil water contents (SWC), and NDVI and SWC values (−0.59 &lt; r &lt; −0.30; p &lt; 0.05). Soil temperature at the depth of 15 cm influenced soil CO2 emissions to a larger extent (r &gt; 0.5; p &lt; 0.01) than air temperature (0.21 &lt; r &lt; 0.33) or soil water content (r &lt; 0.06; p &gt; 0.05). Our data showed strong connections between GHG production and soil chemical parameters of soil pH, nitrogen, potassium, or phosphate concentrations. Biochar application increased soil CO2 emissions but reduced N2O emissions. Our results demonstrated that biochar amendment to soils can help plant growth initially, but might not result in enhanced crop yield. The plant parameters were substantially different between the investigated years for both control and biochar amended parcels; therefore, long-term studies are essential to document the lasting effects of these treatments.

Soil greenhouse gas fluxes from a humid tropical forest and differently managed urban parkland in Singapore

Studies of soil greenhouse gas (GHG) fluxes (CO2, CH4 and N2O) from tropical soils are still scarce and the effects of urban green space management on soil GHG fluxes are poorly addressed. In order to establish reliable global GHG budgets, field measurements of soil GHG fluxes from different land uses and management practices in tropical regions are urgently needed. In this study, soil fluxes of CO2, CH4 and N2O were measured over a period of one year, from a forest and an urban parkland in Singapore. At the parkland site, two additional management practices were investigated, namely compost application to urban lawn and the replacement of lawn by legumes. The average CO2 efflux from the forest soil was 0.17 ± 0.01 g C m−2 h−1 and was 30% lower than that of the parkland soil. The forest soil was a CH4 sink (−36.03 ± 8.80 μg C m−2 h−1), while the parkland soil was a source of CH4 (43.79 ± 9.66 μg C m−2 h−1). Both soils were net emitters of N2O, with the forest soil releasing four times more N2O (23.23 ± 5.10 μg N m−2 h−1) than the parkland soil (6.47 ± 2.52 μg N m−2 h−1). During the entire observation period, compost application increased CO2eq by 30% compared with the untreated parkland soil. Shortly after compost addition, CO2 fluxes significantly increased and remained elevated until the end of the experiment. Soil CH4 emissions also increased, but the effect was small compared to CO2 (<1% CO2eq). Compost amendment caused an immediate short-term peak of N2O emissions. However, after the first day, which was characterized by a heavy rain event, the compost effect on N2O production was negligible. Compared to grass cultivation, legume planting resulted in a 20% reduction of CO2eq. This study shows that conserving mature secondary forests and the cultivation of herbaceous legumes on tropical urban soils, where open lawn spaces are not required, can reduce soil GHG emissions.

Simultaneous tree stem and soil greenhouse gas (CO2 , CH4 , N2 O) flux measurements: a novel design for continuous monitoring towards improving flux estimates and temporal resolution.

Tree stems and soils can act as sources and sinks for the greenhouse gases (GHG) carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O). Since both uptake and emission capacities can be large, especially in tropical rainforests, accurate assessments of the magnitudes and temporal variations of stem and soil GHG fluxes are required. We designed a new flexible stem chamber system for continuously measuring GHG fluxes in a French Guianese rainforest. Here, we describe this new system, which is connected to an automated soil GHG flux system, and discuss measurement uncertainty and potential error sources. In line with findings for soil GHG flux estimates, we demonstrated that lengthening the stem chamber closure time was required for accurate estimates of tree stem CH4 and N2 O flux but not tree stem CO2 flux. The instrumented stem was a net source of CO2 and CH4 and a weak sink of N2 O. Our experimental setup operated successfully in situ and provided continuous tree and soil GHG measurements at a high temporal resolution over an 11-month period. This automated system is a major step forward in the measurement of GHG fluxes in stems and the atmosphere concurrently with soil GHG fluxes in tropical forest ecosystems.

Potential benefits of liming to acid soils on climate change mitigation and food security.

Globally, about 50% of all arable soils are classified as acidic. As crop and plant growth are significantly hampered under acidic soil conditions, many farmers, but increasingly as well forest managers, apply lime to raise the soil pH. Besides its direct effect on soil pH, liming also affects soil C and nutrient cycles and associated greenhouse gas (GHG) fluxes. In this meta-analysis, we reviewed 1570 observations reported in 121 field-based studies worldwide, to assess liming effects on soil GHG fluxes and plant productivity. We found that liming significantly increases crop yield by 36.3%. Also, soil organic C (SOC) stocks were found to increase by 4.51% annually, though soil respiration is stimulated too (7.57%). Moreover, liming was found to reduce soil N2 O emission by 21.3%, yield-scaled N2 O emission by 21.5%, and CH4 emission and yield-scaled CH4 emission from rice paddies by 19.0% and 12.4%, respectively. Assuming that all acid agricultural soils are limed periodically, liming results in a total GHG balance benefit of 633-749TgCO2 -eqyear-1 due to reductions in soil N2 O emissions (0.60-0.67TgN2 O-Nyear-1 ) and paddy soil CH4 emissions (1.75-2.21TgCH4 year-1 ) and increases in SOC stocks (65.7-110TgCyear-1 ). However, this comes at the cost of an additional CO2 release (c. 624-656TgCO2 year-1 ) deriving from lime mining, transport and application, and lime dissolution, so that the overall GHG balance is likely neutral. Nevertheless, liming of acid agricultural soils will increase yields by at least 6.64×108 Mgyear-1 , covering the food supply of 876 million people. Overall, our study shows for the first time that a general strategy of liming of acid agricultural soils is likely to result in an increasing sustainability of global agricultural production, indicating the potential benefit of liming acid soils for climate change mitigation and food security.

Studying greenhouse gas emissions through interactions between phospholipid fatty acid content and soil properties of alpine grassland soil in Northern Tibet, China

This study aimed to gain a better understanding of the carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes due to soil microbial community and soil physicochemical factors in Northern Tibet, China. We selected five types of grassland soils, incubated them under controlled temperature and humidity conditions, and analyzed the relationship between soil greenhouse gas (GHG) emissions and soil phospholipid fatty acids (PLFAs), soil bulk density, pH, soil organic carbon (SOC), dissolved organic carbon total nitrogen (TN), and total inorganic nitrogen content. The results showed that GHG emissions varied across different types of alpine grassland soils. The highest GHG fluxes occurred in alpine meadows, while the lowest fluxes occurred in alpine deserts, which could be explained based on the soil nutrient contents, including SOC and TN. In total, 23 microbial biomarker PLFAs were extracted from five types of alpine grassland soils to model the relationships between PLFAs and GHG emissions (or absorption) using backward regression analysis, over a three-month incubation experiment. Bacterial groups were responsible for CO2 emissions, while the initial quantities of bacteria and the fungi: bacteria ratio influence N2O emissions. Soils were the CH4 sink, and CH4 amount was influenced by the initial quantities of methane-oxidizing bacterial biomarkers (18:1ω5c) in Northern Tibet. Therefore, our findings showed that the microbial community structure and soil properties jointly explains the variation in soil GHG fluxes under specific environmental condition.