Response Of Greenhouse Gas Emissions Research Articles

Rapid Responses of Greenhouse Gas Emissions and Microbial Communities to Carbon and Nitrogen Addition in Sediments.

Massive labile carbon and nitrogen inputs into lakes change greenhouse gas emissions. However, the rapid driving mechanism from eutrophic and swampy lakes is not fully understood and is usually contradictory. Thus, we launched a short-term and anaerobic incubation experiment to explore the response of greenhouse gas emissions and microbial communities to glucose and nitrate nitrogen (NO3--N) inputs. Glucose addition significantly increased CH4 and CO2 emissions and decreased N2O emissions, but there were no significant differences. NO3--N addition significantly promoted N2O emissions but reduced CH4 accumulative amounts, similar to the results of the Tax4Fun prediction. Bacterial relative abundance changed after glucose addition and coupled with the abundance of denitrification genes (nirS and nirK) decreased while maintaining a negative impact on N2O emissions, considerably increasing methanogenic bacteria (mcrA1) while maintaining a positive impact on CH4 emissions. Structural equation modeling showed that glucose and NO3--N addition directly affected MBC content and greenhouse gas emissions. Further, MBC content was significantly negative with nirS and nirK, and positive with mcrA1. These results significantly deepen the current understanding of the relationships between labial carbon, nitrogen, and greenhouse emissions, further highlighting that labile carbon input is the primary factor driving greenhouse gas emissions from eutrophic shallow lakes.

Responses of greenhouse gas emissions to increased precipitation events in different ecosystems: A meta-analysis

Changes in precipitation patterns induced by climate change exacerbate the phenomenon by stimulating carbon (C) and nitrogen (N) processes in terrestrial ecosystems, leading to increased emissions of soil greenhouse gases (GHGs). However, the response of soil GHG fluxes across various global ecosystems under conditions of increased precipitation (IP) and extreme precipitation (EP) remains unclear. This study conducted a meta-analysis to examine the effects of IP and EP on soil GHG fluxes, synthesizing data from 49 published studies worldwide, and explored potential influencing factors. The results indicated that (1) IP significantly elevated CO2 emissions by 10.2 % and N2O emissions by 61.7 %, and did not impact CH4 emissions. EP treatment significantly increased N2O emissions by 61.8 %, CO2 emissions by 13.3 %, and CH4 emissions by 3.2 %. (2) Under IP treatment, significant differences in soil GHGs among various ecosystems were observed (P < 0.01). Among the three analyzed ecosystems (grassland, forest, and farmland), the response ratios of CO2 (30.4 %), N2O (61.8 %), and soil respiration (37.5 %, excluding plant respiration) were highest in the forest ecosystem and lowest in the grassland. (3) The response of CO2 flux to precipitation was most affected by soil dissolved organic C (P < 0.001) and microbial biomass C (P < 0.001). The key factor affecting the change in N2O flux was NH4+-N (P < 0.001). These findings provide a new perspective for understanding the effects of IP on soil C and N cycles in the context of global climate change.

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.

Responses of greenhouse gas emissions to aeration coupled with functional membrane during industrial-scale composting of dairy manure: Insights into bacterial community composition and function

Greenhouse gas (GHG) emissions from manure management processes deserve more attention. Using three industrial-scale experiments, this study comprehensively evaluated the effects of different aeration coupled with semi-permeable membrane-covered strategies on the structure and function of bacterial communities and their impact on GHG emissions during dairy manure aerobic composting. The succession of the bacterial communities tended to be consistent for similar aeration strategies. Ruminiclostridium and norank_f__MBA03 were significantly positively correlated with the methane emission rate, and forced aeration coupled with semi-permeable membrane-covered decreased GHG emissions by inhibiting these taxa. Metabolism was the most active function of the bacterial communities, and its relative abundance accounted for 75.69%–80.23%. The combined process also enhanced carbohydrate metabolism and amino acid metabolism. Therefore, forced aeration coupled with semi-permeable membrane-covered represented a novel strategy for reducing global warming potential by regulating the structure and function of the bacterial communities during aerobic composting of dairy manure.

Is green manure a viable substitute for inorganic fertilizer to improve grain yields and advance carbon neutrality in paddy agriculture?

Green manure is a widely applied to increase grain yield, while it also attributes to greenhouse gas (GHG) emissions in agriculture ecosystems. Combining green manure with inorganic fertilizer inputs is a common practice that can influence soil GHG emissions and grain yield, however, its impacts on grain yield and global warming potential (GWP) under different initial soil conditions before rotating experiments and agronomic management in paddy fields remain unclear. We synthesized 508 data pairs to evaluate the responses of CO2 emissions, CH4 emissions, N2O emissions, and grain yield to combined inputs of green manure plus inorganic fertilizer compared with only inorganic fertilizer application. Our findings indicate that both inorganic fertilizer plus extra green manure (GM-E) and green manure substitutes for inorganic fertilizer (GM-S) could increase CO2 emissions (22.5 %−76.8 %), CH4 emissions (100 %−103 %), N2O emissions (29.8 %−50.9 %), and yield (2.21 %−19.6 %). Except for GM-E, which showed a non-significant increase in grain yield. The initial soil properties before rotating experiments, the types and timing of green manure application were key drivers of GHG emissions and yield, and extra green manure applied in areas with low initial soil pH and high C:N can increase GWP and yield. Overall, the mixed green manure application had greater impact than leguminous or non-leguminous green manure applied alone. The responses of GHG emissions and yield to GM-S were modulated by mean annual precipitation and initial soil properties before rotating experiments, and green manure substitutes for inorganic fertilizer in areas with high initial soil pH and low C:N can increase GWP and yield. Meanwhile, excessive precipitation caused a reduction in yield and a significant increase in GWP intensity. Our results showed that extra green manure applications of less than 68.1 kg N ha−1 would not significantly increase GWP. Therefore, an effective green manure strategy can achieve a win-win situation for the dual challenge of agricultural production and climate change mitigation.

Soil fauna alter the responses of greenhouse gas emissions to changes in water and nitrogen availability

Fertilization and drought are two of the most important global change drivers that impacting greenhouse gas (GHG) emissions. Soil organisms are among the fundamental biotic drivers of biogeochemical cycles and can play critical roles in mitigating global change. However, the contributions of soil macrofauna in explaining the responses of GHG emissions to fertilization and drought remain poorly understood. Here, we designed a three-factor microcosm experiment to examine how soil macrofauna (no fauna, earthworms, and millipedes) alter the responses of CO2, N2O, and CH4 emissions, as well as the C and N contents in response to contrasting levels of N (N0: without N addition, N+: N addition) and available soil water (40% and 60% of soil water holding capacity). We show that soil fauna were significant regulators of CO2 and N2O emissions in response to changes in water and N availability, as supported by multiple identified statistical interactions. Millipedes were observed to reduce the positive influence of soil water availability on soil CO2 emissions in response to the addition of N. Similarly, earthworms weakened the effects of elevated N and water availability on soil N2O emissions. Moreover, CH4 emissions occurred only when millipedes were present. The structural equation models revealed that earthworms and millipedes modified soil CO2 and N2O emissions through their influences on soil total dissolved nitrogen and microbial biomass carbon. Overall, this study demonstrated that soil macrofauna can notably mediate the responses of GHG emissions and soil biogeochemical cycles to global environmental changes.

Short-term Response of Greenhouse Gas Emissions from Precision Fertilization on Barley

Precision fertilization is a promising mitigation strategy to reduce environmental impacts of N-fertilization, but the effective benefits of variable-rate fertilization have not yet been fully demonstrated. We evaluated the short-term response (23 days) of GHGs emissions following variable-rate fertilization on barley. Yields, biomass (grains + straw) and different N-use indicators (N uptake, grain protein concentration, recovery efficiency, physiological efficiency, partial factor productivity of applied nutrient, agronomic efficiency and N surplus) were compared. Four N fertilization treatments were performed: (i) conventional– 150 kg ha−1; (ii) variable with granular fertilizer; (iii) variable with foliar liquid supplement; (iv) no fertilization. According to proximal sensing analysis (Greenseeker Handheld) and crop needs, both variable-rate treatments accounted for 35 kg N ha−1. Cumulative GHGs emissions were not significantly different, leading to the conclusion that the sensor-based N application might not be a GHGs mitigation strategy in current experimental conditions. Results showed that both site-specific fertilizations ensured the maintenance of high yields with a significant N rate reduction (approximately by 75%) and a N use improvement. Variable-rate N fertilization, due to similar yields (~6 tons ha−1) than conventional fertilization and higher protein content in foliar treatment (14%), confirms its effectiveness to manage N during the later phases of growing season.

Effect of warming on the carbon flux of the alpine wetland on the Qinghai–Tibet Plateau

Under the scenario of global warming, the response of greenhouse gas emissions from alpine wetlands remains unclear. In this study, fluxes of CO2 and CH4 were measured during daytime for the microtopographic features of hollows and hummocks in a wetland in the Tibetan Plateau under two elevated temperatures, increments of ∼1°C (T1 treatment) and ∼2°C (T2 treatment), during the growing season in 2019. The results showed that warming significantly increased the cumulative net ecosystem CO2 exchanges (NEE) for both microtopographic features in the wetland compared to the control due to a combination of the increased gross primary production (GPP) with an increase in ecosystem respiration (ER). Similarly, warming also increased cumulative CH4 emission significantly. The effect was stronger for T2 than that for T1 for all component fluxes (GPP, ER, NEE, and CH4). Generally, NEE and CH4 fluxes both rose at first and then decreased. NEE peaked at the end of July for both hollows and hummocks, while CH4 emissions peaked in the middle of August. The cumulative CH4 emissions from the hummocks were significantly higher than those of the hollows, and CH4 emissions under illumination were significantly higher than those in darkness, which may be caused by the irradiation-sensitive vegetable internal convective gas transport system which diffuses CH4 from the pedosphere. This study revealed that warming strengthened the function of the CO2 sink but also increased CH4 emissions from the alpine wetlands on the Qinghai–Tibet Plateau.

Energy R&D expenditure, bioethanol consumption, and greenhouse gas emissions in the United States: Non-linear analysis and political implications

Although there have been international frameworks for limiting global warming, however, sustainable actions are not on the same track in terms of speed and scale due to the lack of an explicit pathway. A large strand of the literature has examined the emissions-mitigating effect of R&D expenditure and biofuel energy consumption but in a linear framework and disregarded the factors that cause non-linearity. In that respect, this study aims to offer a new perspective on the asymmetric response of greenhouse gas emissions to government energy R&D expenditure and biofuel use in the United States over the 1981–2020 period using a nonlinear time series approach. The results confirm the asymmetrical relationships between government energy R&D, biofuel use, and greenhouse gas emissions. In the long run, a positive shock in energy R&D expenditure reduces greenhouse gas emissions, while a negative shock increases them. More importantly, the reducing effect of positive shock is more dominant than the enhancing effect of negative shock in energy R&D. Similarly, it is shown that the reducing effect of a positive shock on ethanol consumption on greenhouse gas emissions is stronger than the increasing effect of a negative shock. After the estimations, this paper presents two critical implications, political and practical. (i) The government's energy R&D expenditures and biofuels have an important role in the fight against climate change and the clean energy transformation process. (ii) Researchers should also consider asymmetric effects when examining energy technologies, renewable energy, and environmental issues.

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.

Responses of greenhouse gas emissions and soil carbon and nitrogen sequestration to field management in the winter season: A 6-year measurement in a Chinese double-rice field

Stubble return, drainage, and tillage are common practices in rice agriculture, but their integrated effects in the winter season on greenhouse gas (GHG) emissions and soil organic carbon (SOC) and total nitrogen (STN) sequestration remain poorly known. A six-year experiment was carried out in a double-rice field to measure CH4 and N2O fluxes and SOC and STN contents, and then the net global warming potential (GWP) and yield-scaled GWP were estimated. Shifting the fields from no management in tradition to tillage in the winter season tended to reduce total CH4 emissions of double-rice seasons by 14.7%, and it significantly decreased the emissions by 28.3% under drainage conditions. An additional reduction of 27.3% was further found without returning stubble. Therefore, winter tillage and drainage substantially reduced total GWP by 28.0%, in particular, a larger decrease (47.2%) was observed by no stubble return though N2O emissions were strongly stimulated by 82.1%. Moreover, winter tillage significantly reduced SOC sequestration rate while played little role in STN sequestration rate. However, winter tillage with stubble return (2.5–4.1 tha−1) under drainage conditions showed the largest SOC (1.58 t Cha−1yr−1) and STN (0.15 t N ha−1 yr−1) sequestration rates. Therefore, the net GWP and yield-scaled GWP were significantly decreased by 227% and 30.5%, respectively. Overall, our results suggest that winter drainage and tillage with stubble incorporation would be an effective management strategy to promote soil C and N sequestration and mitigate GHG emissions from the double-rice fields.

Responses of greenhouse gas emissions to residue returning in China's croplands and influential factors: A meta-analysis

Climate change is a global issue threatening agricultural production and human survival. However, agriculture sector is a major source of global greenhouse gases (GHGs), especially CH4 and N2O. Crop residue returning (RR) is an efficient practice to sequestrate soil carbon and increase crop yields. However, the efficiency of RR to mitigate climate change and maintain food security will be affected by the response of GHG emissions at both per area-scale and per yield-scale. Therefore, a national meta-analysis was conducted using 309 comparisons from 44 publications to assess the responses of GHG emissions to RR in China's croplands. The results indicated that little response of GWP to RR was observed with conditions under lower nitrogen fertilizer input rates (0–120 kg ha−1), mulch retention, returning one time in double cropping systems, returning with half residue, weakly acidic soil (pH 5.5–6.5), initial SOC contents >20 g kg−1, or mean annual precipitation <1000 mm. In order to mitigate climate change and sustain food security, RR combined with paddy-upland rotation, nitrogen fertilizer input rates of 240–360 kg ha−1, and neutral soil (pH 6.5–7.5) could decrease GWP at per unit of crop yield, which ultimately leads to a lower effect on GHGI and a higher crop production efficiency. In-depth studies should be conducted in the future to explore the interactions between various factors influencing GHG emissions under RR conditions. Overall, optimizing the interactions with management and site-specific conditions, potential for regulating GHGs emissions of RR can be enhanced.

Determination of Region of Influence Obtained by Aircraft Vertical Profiles Using the Density of Trajectories from the HYSPLIT Model

Aircraft atmospheric profiling is a valuable technique for determining greenhouse gas fluxes at regional scales (104–106 km2). Here, we describe a new, simple method for estimating the surface influence of air samples that uses backward trajectories based on the Lagrangian model Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT). We determined “regions of influence” on a quarterly basis between 2010 and 2018 for four aircraft vertical profile sites: SAN and ALF in the eastern Amazon, and RBA and TAB or TEF in the western Amazon. We evaluated regions of influence in terms of their relative sensitivity to areas inside and outside the Amazon and their total area inside the Amazon. Regions of influence varied by quarter and less so by year. In the first and fourth quarters, the contribution of the region of influence inside the Amazon was 83–93% for all sites, while in the second and third quarters, it was 57–75%. The interquarter differences are more evident in the eastern than in the western Amazon. Our analysis indicates that atmospheric profiles from the western sites are sensitive to 42–52.2% of the Amazon. In contrast, eastern Amazon sites are sensitive to only 10.9–25.3%. These results may help to spatially resolve the response of greenhouse gas emissions to climate variability over Amazon.

Different Responses of Greenhouse Gas Emissions to Straw Application at Different Seasons in Northeast China

Although straw return plays a role in regulating greenhouse gas (GHG) emissions from rice paddy fields, little quantitative information is available on the extent at different periods. In this study, gas samples were collected during the rice growing period from an in-situ experiment comprising three treatments: no straw return (CK); straw return in the autumn (SR-A), and; straw return in the spring (SR-S). The results showed that SR-A and SR-S enhanced CO2 and CH4 emissions, but reduced N2O emissions during the growing period. The total cumulative CO2 emissions over the entire growing period in the SR-S treatment reached 20,383.72 kg ha−1, significantly higher than those of the SR-A and CK treatments. CH4 emissions for all the growing periods were in the order SR-S > SR-A > CK. The CK and SR-S treatments released the most and least N2O during the different periods, respectively. The global warming potential (GWP) of CH4 released by the SR-S, SR-A and CK treatments reached 26,055.37 kg CO2 eq. ha−1, 12,643.27 kg CO2 eq.1, and 9,237.55 kg CO2 eq.1, accounting for 55.80%, 40.35%, and 35.99% of the total GWP, respectively. These results can contribute to management of agricultural GHGs in this region.

Short-term responses of greenhouse gas emissions and ecosystem carbon fluxes to elevated ozone and N fertilization in a temperate grassland

Growing evidence suggests that tropospheric ozone has widespread effects on vegetation, which can contribute to alter ecosystem carbon (C) dynamics and belowground processes. In this study, we used intact soil mesocosms from a semi-improved grassland and investigated the effects of elevated ozone, alone and in combination with nitrogen (N) fertilization on soil-borne greenhouse gas emissions and ecosystem C fluxes. Ozone exposure under fully open-air field conditions was occurred during the growing season. Across a one-year period, soil methane (CH4) and nitrous oxide (N2O) emissions did not differ between treatments, but elevated ozone significantly depressed soil CH4 uptake by 14% during the growing season irrespective of N fertilization. Elevated ozone resulted in a 15% reduction of net ecosystem exchange of carbon dioxide, while N fertilization significantly increased ecosystem respiration during the growing season. Aboveground biomass was unaffected by elevated ozone during the growing season but significantly decreased by 17% during the non-growing season. At the end of the experiment, soil mineral N content, net N mineralization and extracellular enzyme activities (i.e., cellobiohydrolase and leucine aminopeptidase) were higher under elevated ozone than ambient ozone. The short-term effect of single application of N fertilizer was primarily responsible for the lack of the interaction between elevated ozone and N fertilization. Therefore, results of our short-term study suggest that ozone exposure may have negative impacts on soil CH4 uptake and C sequestration and contribute to accelerated rates of soil N-cycling.

Response of greenhouse gas emissions and microbial community dynamics to temperature variation during partial nitrification

This study investigated the greenhouse gas emission characteristics and microbial community dynamics with the variation of temperature during partial nitrification. Low temperature weakened nitrite accumulation, and partial nitrification would shift to complete nitrification easily at 15 °C. Based on CO2 equivalents (CO2-eq), partial nitrification process released 2.7 g of greenhouse gases per gMLSS per cycle, and N2O accounted for more than 98% of the total CO2-eq emission. The total CO2-eq emission amount at 35 °C was 45.6% and 153.4% higher than that at 25 °C and 15 °C, respectively. During partial nitrification, the microbial community diversity greatly declined compared with seed sludge. However, the diversity was enhanced at low temperature. The abundance of Betaproteobacteria at class level increased greatly during partial nitrification. Proteobacteria abundance declined while Nitrospira raised at low temperature. The nosZ community abundance was not affected by temperature, although N2O emission was varied with the operating temperature.

Temporal response of soil prokaryotic communities to acidification and alkalization under laboratory conditions

Soil pH plays an important role in shaping the structure and diversity of prokaryotic community. Altered pH regimes may change prokaryotic community composition by selecting species or groups with different ecological strategies to optimize their fitness. However, it remains unresolved whether prokaryotic communities exhibit deterministic (phylogenetically conserved) or stochastic (phylogenetically overdispersed) responses to pH. In this study we investigated the responses of greenhouse gas emissions and prokaryotic community structure to pH using three-month incubation experiments by adjusting an artificial pH gradient from 4.5 to 8.5. We found decreasing OTUs richness after three months of incubation. Phylogenetic clustering of the prokaryotic community was observed at earlier incubation times whereas greater phylogenetic distance of the prokaryotic community was found at later incubation time. Our results evidenced differential responses of various soil bacterial taxa to the changes in pH. Relative abundances of bacterial phyla and classes of main ecological groups of soil prokaryotes, oligotrophs and copiotrophs, changed significantly along an artificial pH gradient at various incubation times. Relative abundance of Acidobacteria significantly increased with pH at the start of experiment, while opposite trend was observed after 90 days of incubation. In contrast, the relative abundance of Bacteroidetes showed opposite response as Acidobacteria to elevated pH gradient during various incubation time. Methane emissions increased with pH as well as with incubation time, but carbon dioxide and nitrous oxide only increased with incubation time.

Weak response of greenhouse gas emissions to whole lake N enrichment

AbstractGlobal warming and land use scenarios suggest increased 21st century nitrogen (N) inputs to aquatic systems. Nitrogen affects in‐lake processing and, potentially, atmospheric exchange of greenhouse gases, probably being most relevant in unproductive systems. Here, we test for the first time the effect of a whole‐lake experimental increase (threefold) in external nitrate loads on the atmospheric exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from N‐limited unproductive boreal lakes. Nitrate enrichment effects were assessed within a paired Before/After‐Control/Impact framework based on 2‐hourly to biweekly surface‐water sampling of dissolved gas concentrations, and monthly whole‐lake inventory surveys, carried out over 4 yrs in six lakes. Nitrate enrichment did not affect gas exchange during summer stratification and whole‐lake gas inventories during summer and winter stratification. This finding specifically emphasizes the modest role of internal carbon fixation for the CO2 dynamics of unproductive boreal lakes. A global synthesis of 52 published studies revealed a wide range of nutrient fertilization effects, both in systems similar to our experimental lakes, and other more productive systems. Effects depended mainly on the spatiotemporal scale of the study and became more pronounced when N enrichment was combined with phosphorous. Conclusively, although short‐term and habitat‐specific effects can occur, changes in N supply have only weak whole‐ecosystem effects on greenhouse gas emissions from unproductive boreal lakes.

Response of greenhouse gas emissions from three types of wetland soils to simulated temperature change on the Qinghai-Tibetan Plateau

Wetlands emit a large quantity of greenhouse gases into the atmosphere and contribute significantly to global warming. The Qinghai-Tibetan Plateau, known as the “Third Pole” of the earth, contains abundant and diverse wetlands. Due to increasing human-induced pressures such as reclamation, overgrazing and climate change, many plateau wetlands have been degraded or destroyed. Until now, the response of soil greenhouse gas emissions to extreme summer temperatures in the plateau wetlands remains unknown. In this study, we collected 36 soil samples from riverine, lacustrine and palustrine wetlands on the Qinghai-Tibetan Plateau. We compared the carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions from soils incubated aerobically at 7, 12, and 19 °C. The results showed that the emissions of CH4 and N2O but not CO2 were significantly affected by the simulated temperature change. The N2O emission rate was considerably higher in palustrine wetlands compared with lacustrine and riverine wetlands. However, the CO2 and CH4 emissions did not differ significantly among the three wetland types. The ratio of CO2 to CH4 production increased with increasing incubation temperatures. The global warming potential of greenhouse gases at 19 °C was approximately 1.18 and 2.12 times greater than that at 12 and 7 °C, respectively. Our findings suggest that temperature change has a strong effect on soil greenhouse gas emissions and global warming potential of wetlands on the Qinghai-Tibetan Plateau, especially palustrine wetlands. Therefore, targeted strategies should be developed to mitigate the potential impacts of climate warming on the plateau.

Temperature sensitivity of soil carbon dioxide and nitrous oxide emissions in mountain forest and meadow ecosystems in China

An incubation experiment was conducted at three temperature levels (8, 18 and 28 °C) to quantify the response of soil CO2 and N2O emissions to temperature in three ecosystems (pine forest, oak forest, and meadow) located in the Qinling Mountains of China, which are considered to be susceptible to disturbance and climate changes, especially global warming. The soil CO2 emission rates increased with temperature and decreased with soil depth; they were the highest in the oak forest (broadleaf forest) and were lower in the pine forest (coniferous forest) and the meadow ecosystem. However, there was no significant difference in the soil N2O emission rates among the three ecosystems. The temperature sensitivity of CO2 and N2O was higher in the forest than in the meadow ecosystem. The Q10 values (temperature sensitivity coefficient) for CO2 and N2O were 1.07–2.25 and 0.82–1.22, respectively, for the three ecosystems. There was also evidence that the CO2 and N2O emission rates were positively correlated. The soil characteristics exhibited different effects on CO2 and N2O emissions among different ecosystems at the three temperature levels. Moreover, the soil dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA) and nitrate (NO3−) were important factors for CO2 emissions, whereas the soil ammonium (NH4+) and pH were the major controllers of N2O emissions. Unexpectedly, our results indicated that CO2 emissions are more sensitive to increasing temperature than N2O, noting the different feedback of CO2 and N2O emissions to global warming in this region. The different responses of greenhouse gas emissions in different forest types and a meadow ecosystem suggest that it is critical to conduct a comprehensive investigation of the complex mountain forest and meadow ecosystem in the transitional climate zone under global warming. Our research results provide new insight and advanced understanding of the variations in major greenhouse gas emissions (CO2 and N2O) and soil characteristics in response to warming.