Soil CO2 Production Research Articles

Effects of inorganic nitrogen enrichment on soil CH4 and CO2 production in freshwater and mesohaline marshes across six estuaries in China

Eutrophication is an important environmental stressor in coastal wetlands that alters ecosystem processes including primary production and the carbon cycle. However, how different nitrogen eutrophication scenarios may affect CH4 and CO2 production along a salinity gradient in coastal wetlands is poorly known. We collected the surface soil samples from both tidal freshwater and mesohaline Phragmites australis marshes in six main estuaries in China and conducted inorganic nitrogen enrichment anaerobic incubation experiments. Background soil CH4 and CO2 production rates were strongly correlated with total nitrogen but not salinity. On average, nitrate enrichment decreased soil CH4 and CO2 production rates by ca. 20 % in freshwater marsh and 16–43 % in mesohaline marshes, whereas ammonium enrichment decreased CO2 production by ca. 26–30 % but had no effect on CH4 production. Salinity was not an important mitigating factor in either eutrophication scenario. In most cases, nitrogen addition decreased the extracellular enzyme activities of β-1,4-glucosidase and cellobiohydrolase, but increased the activity of β-N-acetyl glucosaminidase, phenol oxidase and peroxidase. Nitrate addition decreased the mcrA gene abundance on average by 34–35 % but ammonium addition had insignificant effect. Total nitrogen availability was an important driver of CH4 and CO2 production rates in these tidally influenced coastal wetlands. Our results showed that tidal marshes with salinity < 15 ppt had similar soil CH4 production rates, and increasing inorganic nitrogen eutrophication might lower soil microbial carbon gas production in both tidal freshwater and mesohaline marshes.

Influence of Biomass Amendments on Soil CO2 Concentration and Carbon Emission Flux in a Subtropical Karst Ecosystem

Soil in karst areas is rare and precious, and karst carbon sinks play an important role in the global carbon cycle. Therefore, the purpose of karst soil improvement is to improve soil productivity and a carbon sink effect. Biomass amendment experiments in this study included three schemes: filter mud (FM), filter mud + straw + biogas slurry (FSB), and filter mud + straw + cow manure (FSC). The characteristics of soil CO2 production, transport, and the effect on soil respiration carbon emissions in two years were compared and analyzed. The results were as follows: 1. The rate, amount, and depth of CO2 concentration were affected by the combinations with biogas slurry (easy to leach) or cow manure (difficult to decompose). 2. The diurnal variation curves of soil respiration in the FSB- and FSC-improved soils lagged behind those in the control soil for three hours. While the curves of FM-improved soil and the control soil were nearly the same. 3. Soil–air carbon emissions increased by 35.2 tCO2/(km2·a−1) under the FM scheme, decreased by 212.9 tCO2/(km2·a−1) under the FSB scheme, and increased by 279.5 tCO2/(km2·a−1) under the FSC scheme. The results were related to weather CO2 accumulation in the deep or surface layers under different schemes.

Soil priming effect in the organic and mineral layers regulated by nitrogen mining mechanism in a temperate forest

AbstractSoil organic carbon (SOC) in temperate forests is a crucial part of the global C cycle. The C and nitrogen (N) inputs may greatly increase in forest ecosystems affected by atmospheric CO2 concentration, N deposition, and other climate change, which may further affect SOC dynamics in temperate forests. Nevertheless, how C and N inputs interact to influence the soil priming effect (PE) in the organic and mineral layers of temperate forests remains unclear. Here, we used easily available C and N sources, such as 13C‐glucose with 2% SOC contents and ammonium nitrate (input C:N ratio = 10), to examine the effects and mechanisms of exogenous C and N inputs on soil CO2 production and PE in both soil layers of a temperate forest. Our research revealed that exogenous C input caused a positive PE in both soil layers, with the mineral layer showing a larger PE per unit of SOC than the organic layer (OL). Although C input increased C loss from native SOC, soil net C accumulation still increased. The C and N inputs decreased the soil PE in both soil layers, suggesting that N input alleviates substrate N limitation and weakens microbial N mining in both soil layers. Meanwhile, the C and N inputs increased the exogenous C remaining in the organic layer, which was beneficial for soil C sequestration. Compared to the organic layer, the response of the mineral layer to C and N inputs was weaker. This study suggests that C and N interact to affect PE on SOC decomposition and this interaction should be considered in modeling and prediction of soil C cycling.

Interannual precipitation controls on soil CO2 fluxes in high elevation conifer and aspen forests

Long-term soil CO2 emission measurements are necessary for detecting trends and interannual variability in the terrestrial carbon cycle. Such records are becoming increasingly valuable as ecosystems experience altered environmental conditions associated with climate change. From 2013 to 2021, we continuously measured soil CO2 concentrations in the two dominant high elevation forest types, mixed conifer and aspen, in the upper Colorado River basin. We quantified the soil CO2 flux during the summer months, and found that the mean and total CO2 flux in both forests was related to the prior winter’s snowfall and current summer’s rainfall, with greater sensitivity to rainfall. We observed a decline in surface soil CO2 production, which we attributed to warming and a decrease in amount and frequency of summer rains. Our results demonstrate strong precipitation control on the soil CO2 flux in mountainous regions, a finding which has important implications for carbon cycling under future environmental change.

Unknown bacterial species lead to soil CO2 emission reduction by promoting lactic fermentation in alpine meadow on the Qinghai-Tibetan Plateau

Highly variable soil microbial respiration among grasslands has been identified as a major cause of uncertainty in regional carbon (C) budget estimation in the Qinghai-Tibetan Plateau; microbial metabolism mechanisms might explain this variation, but remain elusive. Therefore, we investigated soil CO2 production in incubated soils and detected the associated functional genes at four sampling sites from two major alpine grasslands on the Qinghai-Tibetan Plateau. The results showed that the cumulative CO2 emissions from alpine meadow soils were 71 %–83 % lower than those from alpine steppe soils. Both the enriched genes abundance encoding fermentation and glycolysis (Embden-Meyerhof pathway (EMP)) and the diminished genes encoding tricarboxylic acid cycle (TCA) and phosphate pentose pathway (PPP) explained the CO2 emission reduction in the alpine meadow soils. The EMP: PPP and fermentation: TCA cycle ratios in alpine meadow soils were 1.45- and 1.50-fold higher than those in alpine steppe soils, respectively. Such shifts in metabolic pathways were primarily caused by the increasing dominance of an unknown species of Desulfobacteraceae with high glycolytic potential, carrying a higher abundance of ldh genes during fermentation. These unknown species were promoted by warmer temperatures and higher precipitation in the alpine meadows. Further studies on the unknown species would enhance our understanding and predictability of C cycling in alpine grasslands.

Changes in aggregate-associated carbon and microbial respiration affected by aggregate size, soil depth, and altitude in a forest soil

This study investigates the variations of aggregate-associated organic carbon (OC) and microbial respiration (MR) with respect to aggregate size, soil depth, and land altitude in a forest soil. The research was conducted in Arasbaran forest, East Azerbaijan province, Iran. Four sites were selected at different altitudes: 0–600 m, 600–1200 m, 1200–1800 m, and 1800–2400 m above sea level (a.s.l.), along the north-facing slope of the forest region. Soil samples were collected at five depths: 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm, with three replications for each depth. The soil samples were then fractioned into four aggregate size classes: <0.053 mm, 0.053–0.25 mm, 0.25–2 mm, and >2 mm. Both soil samples and aggregate fractions were analyzed for OC content and MR. The results revealed that OC content and MR in both soil samples and aggregate fractions increased with altitude and decreased with soil depth. Moreover, aggregate-associated OC increased with aggregate size. Specifically, as soil aggregate sizes increased from <0.053 mm to >2 mm at different altitudes, the mean occluded OC content of aggregates increased by approximately four times. Similarly, the mean aggregate-associated MR intensified eight times with the increase in aggregate size. A significant positive correlation was also observed between OC and MR rates of all aggregates. Furthermore, aggregates larger than 2 mm exhibited the highest contribution to the total soil OC storage (47.47–57.22%) and CO2 production rate (20–21%). These findings underscore the critical role of large macro-aggregates (>2 mm) in soil carbon storage and microbial activity, particularly in surface soils at higher altitudes.

Dimension does matter: carbon-based substances with different dimensions exhibit opposite effects on soil CO2 and CH4 production

Dimension does matter: carbon-based substances with different dimensions exhibit opposite effects on soil CO2 and CH4 production

Responses of dissolved organic carbon to freeze–thaw cycles associated with the changes in microbial activity and soil structure

Abstract. Arctic warming accelerates snowmelt, exposing soil surfaces with shallow or no snow cover to freeze–thaw cycles (FTCs) more frequently in early spring and late autumn. FTCs influence Arctic soil C dynamics by increasing or decreasing the amount of dissolved organic carbon (DOC); however, mechanism-based explanations of DOC changes that consider other soil biogeochemical properties are limited. To understand the effects of FTCs on Arctic soil responses, we designed microcosms with surface organic soils from Alaska and investigated several soil biogeochemical changes for seven successive temperature fluctuations of freezing at −9.0 ± 0.3 ∘C and thawing at 6.2 ± 0.3 ∘C for 12 h each. FTCs significantly changed the following soil variables: soil CO2 production (CO2), DOC and total dissolved nitrogen (TDN) contents, two DOC quality indices (SUVA254 and A365 / A254), microaggregate (53–250 µm) distribution, and small-sized mesopore (0.2–10 µm) proportion. Multivariate statistical analyses indicated that the FTCs improved soil structure at the scale of microaggregates and small-sized mesopores, facilitating DOC decomposition by soil microbes and changes in DOC quantity and quality by FTCs. This study showed that FTCs increased soil CO2 production, indicating that FTCs affected DOC characteristics without negatively impacting microbial activity. Soil microaggregation enhanced by FTCs and the subsequent increase in microbial activity and small-sized pore proportion could promote DOC decomposition, decreasing the DOC quantity. This study provides a mechanism-based interpretation of how FTCs alter DOC characteristics of the organic soil in the active layer by incorporating structural changes and microbial responses, improving our understanding of Arctic soil C dynamics.

Imprints of Millennial-Scale Monsoonal Events during the MIS3 Revealed by Stalagmite δ13C Records in China

Regions located on the Chinese Loess Plateau are sensitive to changes in the Asian monsoon because they are on the edge of the monsoon region. Based on six 230Th experiments and 109 sets of stable isotope data of LH36 from Lianhua Cave, Yangquan City, Shanxi Province, we obtained a paleoclimate record with an average resolution of 120 years from 54.5 to 41.1 ka BP during the MIS3 on the Chinese Loess Plateau. Both the Hendy test and the replication test indicated an equilibrium fractionation of stable isotopes during the stalagmite deposition. Comparison with four other independently-dated, high-resolution stalagmite δ13C records between 29°N and 41°N in the Asian monsoon region shows that the stalagmite δ13C records from different caves have good reproducibility during the overlapped growth period. We suggest that speleothem δ13C effectively indicates soil CO2 production in the overlying area of the cave, reflecting changes in the cave’s external environment and in the Asian summer monsoon. Five millennial-scale Asian summer monsoon intensification events correspond to the Dansgaard–Oeschger 10–14 cycles recorded in the Greenland ice core within dating errors, and the weak monsoon processes are closely related to stadials in the North Atlantic. The spatial consistency of stalagmite δ13C records in China suggests that the Asian summer monsoon and the related regional ecological environment fluctuations sensitively respond to climate changes at northern high latitudes through sea-air coupling on the millennial timescale.

Relationship between soil CO2 fluxes and soil moisture: Anaerobic sources explain fluxes at high water content

Soil moisture is a known environmental factor influencing carbon dioxide (CO2) emissions and therefore represents an important variable in predictive models. Establishing relationships between soil CO2 emissions and soil moisture has long focused on the role of soil organic carbon mineralization by aerobic respiration. This approach, which generally yields a bell-shaped relationship establishing maximum CO2 production at moderate soil moisture, ignores anaerobic processes as a potential source of CO2. To decouple the effects of soil moisture and O2, we conducted a factorial batch experiment by incubating soil samples at different imposed moisture contents (30%, 45%, 65%, 80%, and 100% water-filled pore space; WFPS) at 25 °C, under both oxic (normal air) and anoxic (N2 atmosphere) headspace conditions. Gas fluxes measured in the oxic incubations show that CO2 fluxes were maximal (31.2 ± 1.8 nmol cm−3 soil hr-1) at moderate moisture content (65% WFPS), as commonly reported. However, contrary to previous models that predict negligible CO2 fluxes under fully saturated conditions due to O2 limitation, substantial fluxes of CO2 (18.1 ± 2.2 nmol cm−3 soil hr-1) were measured at 100% WFPS. In the anoxic treatments, CO2 fluxes rose sharply when the moisture content exceeded 65% WFPS, with values at 100% saturation (21.8 ± 2.2 nmol cm−3 soil hr-1), close to the corresponding fluxes in the oxic incubations. Methane (CH4) fluxes in the anoxic incubations increased over time, ultimately reaching parity with the CO2 fluxes at 100% WFPS. To reproduce the soil moisture dependence of the CO2 fluxes, we propose a kinetic model representing both aerobic and anaerobic CO2 production. Together, the gas flux measurements, porewater geochemistry data, and modeling results indicated that at soil moisture contents approaching saturation (≥90%), anaerobic processes were the major source of CO2 in the oxic incubations. Overall, we conclude that existing models may underrepresent soil CO2 production at high soil moisture by not considering anaerobic reaction pathways releasing CO2.

Effects of microbial diversity loss on the stability of CO2 production and N2O emission in agricultural soils.

The relationship between biodiversity and ecosystem stability is a hot topic in ecology. However, current studies focus mainly on aboveground system with plants, little attention has been paid to belowground system with soils. In this study, we constructed three soil suspensions with varying microbial diversity (100, 10-2, 10-6) by the dilution method and inoculated separately into agricultural Mollisols and Oxisols to examine the stability (indicated by resistance and resilience) of soil CO2 production and N2O emission to copper pollution and heat stress. Results showed that the stability of CO2 production in Mollisols was not influenced by microbial diversity loss, while the resistance and resilience of N2O emission in Mollisols were significantly decreased at the 10-6 diversity. In the Oxisols, the resistance and resilience of N2O emission to copper pollution and heat stress started to decrease even at the 10-2 diversity, and the stability of CO2 production decreased at the 10-6 diversity. These results suggested that both soil types and the identity of soil functions influenced the relationship between microbial diversity and the stability of function. It was concluded that soils with ample nutrients and resistant microbial communities tend to have higher functional stability, and that the fundamental soil functions (e.g., CO2 production) are more resistant and resilient than the specific soil functions (e.g., N2O emission) in response to environmental stress.

Soil CO2 in organic and no-till agroecosystems

Increased carbon dioxide (CO2) concentrations in soil profiles could increase carbon sequestration via improved residence times of soil organic carbon (SOC), greater nutrient availability and plant growth, and via other pathways, but the effect of agricultural management techniques on soil CO2 is poorly understood. We used nondispersive infrared (NDIR) CO2 sensors to measure gas-phase CO2 concentrations in 1.50 m soil profiles in paired no-till (NT) and organic (ORG) agricultural systems in the Palouse region of eastern Washington State, USA, to investigate the effect of management on soil CO2. CO2 concentrations were significantly greater in ORG than in NT. The CO2 efflux into the atmosphere estimated using Fick's first law was generally greater in ORG due to both greater diffusivity and stronger concentration gradients observed in ORG. Results demonstrate that organic agriculture may facilitate greater soil CO2 concentrations and production rates. Further research is needed to quantify and understand the role of increased CO2 in soil carbon cycling in agroecosystems.

Source data of manuscript: A rationale for higher ratios of CH4 to CO2 production in warmer anoxic freshwater sediments and soils

Source data of manuscript: A rationale for higher ratios of CH4 to CO2 production in warmer anoxic freshwater sediments and soils

Impacts of thinning activities on boreal peatland forests

Boreal peatland forests are an important source of timber. Recently, timber harvesting has been extended to warmer months, resulting in machinery traffic over unfrozen soils, and leading to higher levels of soil disturbance, such as deeper ruts. Despite this, our knowledge of the impact of soil disturbance on peat physical properties and soil biochemistry is still limited. To address this gap, I conducted a study to examine the effects of soil disturbance caused by harvesting machinery during thinning operations on the soil physical, chemical, and biological properties and vegetation of drained boreal peatland forests. To assess the rate of recovery, I sampled six sites that formed a chronosequence covering 15 years since thinning. The results showed that soil disturbance caused an increase in the bulk density and field capacity of peat, along with a decrease in total porosity. In the vegetation, moss biomass and root production were reduced, but sedge cover increased. Furthermore, recently disturbed areas exhibited greater soil CO2 production potential, as well as higher soil CO2 and CH4 concentrations compared to control areas. However, CO2 and CH4 emissions, microbial communities, and cellulose decomposition rate were not impacted. Although the rate of recovery varied, all studied properties impacted by disturbance were fully recovered within 15 years. As the water retention characteristic (WRC) describes soil structure and its alterations, it a useful for disturbance assessment. Thus, I propose how WRC can be predicted using artificial neural networks. Overall, the study demonstrated that while drained boreal peatlands are sensitive to disturbance, they are also resilient to mechanical soil disturbance caused by thinnings.

Landscape Change Affects Soil Organic Carbon Mineralization and Greenhouse Gas Production in Coastal Wetlands

AbstractPlant invasion and aquaculture activities have drastically modified the landscape of coastal wetlands in many countries, but their impacts on soil organic carbon (SOC) mineralization and greenhouse gas production remain poorly understood. We measured SOC mineralization rate and soil CO2 and CH4 production rates in three habitat types from 21 coastal sites across the tropical and subtropical zones in China: native mudflats (MFs), Spartina alterniflora marshes (SAs), and aquaculture ponds (APs). Landscape change from MFs to SAs or APs increased total and labile fraction of SOC, as well as carbon mineralization rate and greenhouse gas production, but there were no discernible differences in SOC source‐sink dynamics between SAs and APs. SOC mineralization rate was highest in SAs (20.4 μg g−1 d−1), followed by APs (16.9 μg g−1 d−1) and MFs (11.9 μg g−1 d−1), with CO2 as the dominant by‐product. Bioavailable SOC was less than 2% and was turned over within 60 days in all three habitat types. Proliferation of S. alterniflora marshes and expansion of AP construction had resulted in a net increase in soil CO2‐eq production of 0.4–4.3 Tg yr−1 in the last three decades. Future studies will benefit from better census and monitoring of coastal habitats in China, complementary in situ measurements of greenhouse gas emissions, and more sampling in the southern provinces to improve spatial resolution.

Redox Properties of Solid Phase Electron Acceptors Affect Anaerobic Microbial Respiration under Oxygen-Limited Conditions in Floodplain Soils.

Mountain floodplain soils often show spatiotemporal variations in redox conditions that arise due to changing hydrology and resulting biogeochemistry. Under oxygen-depleted conditions, solid phase terminal electron acceptors (TEAs) can be used in anaerobic respiration. However, it remains unclear to what degree the redox properties of solid phases limit respiration rates and hence organic matter degradation. Here, we assess such limitations in soils collected across a gradient in native redox states from the Slate River floodplain (Colorado, U.S.A.). We incubated soils under anoxic conditions and quantified CO2 production and microbial Fe(III) reduction, the main microbial metabolic pathway, as well as the reactivity of whole-soil solid phase TEAs toward mediated electrochemical reduction. Fe(III) reduction occurred together with CO2 production in native oxic soils, while neither Fe(II) nor CO2 production was observed in native anoxic soils. Initial CO2 production rates increased with increasing TEA redox reactivity toward mediated electrochemical reduction across all soil depths. Low TEA redox reactivity appears to be caused by elevated Fe(II) concentrations rather than crystallinity of Fe(III) phases. Our findings illustrate that the buildup of Fe(II) in systems with long residence times limits the thermodynamic viability of dissimilatory Fe(III) reduction and thereby limits the mineralization of organic carbon.

The importance of calcium and amorphous silica for arctic soil CO2 production

Future warming of the Arctic not only threatens to destabilize the enormous pool of organic carbon accumulated in permafrost soils but may also mobilize elements such as calcium (Ca) or silicon (Si). While for Greenlandic soils, it was recently shown that both elements may have a strong effect on carbon dioxide (CO2) production with Ca strongly decreasing and Si increasing CO2 production, little is known about the effects of Si and Ca on carbon cycle processes in soils from Siberia, the Canadian Shield, or Alaska. In this study, we incubated five different soils (rich organic soil from the Canadian Shield and from Siberia (one from the top and one from the deeper soil layer) and one acidic and one non-acidic soil from Alaska) for 6 months under both drained and waterlogged conditions and at different Ca and amorphous Si (ASi) concentrations. Our results show a strong decrease in soil CO2 production for all soils under both drained and waterlogged conditions with increasing Ca concentrations. The ASi effect was not clear across the different soils used, with soil CO2 production increasing, decreasing, or not being significantly affected depending on the soil type and if the soils were initially drained or waterlogged. We found no methane production in any of the soils regardless of treatment. Taking into account the predicted change in Si and Ca availability under a future warmer Arctic climate, the associated fertilization effects would imply potentially lower greenhouse gas production from Siberia and slightly increased greenhouse gas emissions from the Canadian Shield. Including Ca as a controlling factor for Arctic soil CO2 production rates may, therefore, reduces uncertainties in modeling future scenarios on how Arctic regions may respond to climate change.

Centennial-Scale Climatic Oscillations during the Dansgaard–Oeschger 14 Revealed by Stalagmite Isotopic Records from Shouyuangong Cave, Southern China

During the last glacial, Dansgaard–Oeschger (DO) events are mostly characterized by moderate and shorter fluctuations. Here, we present the three-year-resolution stalagmite isotopic record from Shouyuangong Cave (SYG), southern China, revealing a detailed history of Asian summer monsoon (ASM) and local environmental changes during the middle and late period of DO 14. During this period, the SYG1 δ18O is characterized by the persistence of centennial-scale oscillations. These centennial δ18O enrichment excursions are clearly mirrored in the δ13C signal. This correlation suggests that changes in soil CO2 production at this site are closely correlated with centennial-scale ASM variability. Furthermore, power spectrum analysis shows that δ18O and δ13C display the common periodicities consistent with solar activity cycles, implicating a control of solar activity on the ASM and soil humidity. Particularly, weak solar activity generally corresponds to weak ASM and a decline in soil CO2 production. One possible link between them is that external forcing controls the ASM intensity via the thermal contrast between the ocean and land. Subsequently, the balance of soil moisture co-varies with the hydrological responses. Finally, the soil CO2 production is further amplified by ecological effect.

Effects of liming on oxic and anoxic N2O and CO2 production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N2O and CO2 production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH ≥ 7 decreased oxic N2O production by 97–98 % in the Ap1 horizon, 38–50 % in the Bg1 horizon, and 34–36 % in the BC horizon, but increased it by 136–208 % in the C horizon, respectively. Liming decreased anoxic N2O production by 86–94 % and 78–91 % in Ap1 and Bg1 horizons, but increased it by 100–500 % and 50–162 % in BC and C horizons, respectively. Liming decreased N2O/(N2O + N2) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO2 production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil compared to non-AS soil agreed with the respectively higher cumulative oxic N2O production in all horizons, and the higher CO2 production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N2O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO2 equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO2 production and denitrification.

Combined effects of biochar addition with varied particle size and temperature on the decomposition of soil organic carbon in a temperate forest, China

ABSTRACT The particle size of biochar is a vital parameter adjusting the soil CO2 production, whereas the effect of biochar addition with different particle sizeon soil CO2 production is still largely unclear. Furthermore, combined effects of biochar addition and temperature on CO2 production are still unknown. To address this gap, a series of incubation experiments were conducted to examine the single and interactive effects of biochar addition with three particle sizes (1–0.5 mm, 0.5–0.1 mm, and <0.1 mm) and temperature on CO2 production in a temperate forest, China. The soil samples were collected from a poplar (Populus nigra) forest in the sandy area of the ancient Yellow River in western Shandong Province, China. Cumulative CO2 production of fine-grained biochar addition (<0.1 mm) was 88.13–92.67% of that of coarse-grained biochar (1–0.5 mm). The addition of fine-grained biochar decreased CO2 production by reducing soil nitrogen availability (i.e., nitrate and ammonium) and increasing soil pH compared to the coarse-grained biochar. Biochar addition promoted the temperature sensitivity (Q 10) of CO2 production by increasing the relative abundance of recalcitrant carbon fractions. Interactive effects of biochar addition and increasing temperature was synergistic due to the raising Q 10 value of CO2 production. Our results highlight the importance of particle size of biochar on CO2 production, less particle size of biochar, the less CO2 production. We suggest that the simultaneous effect of biochar addition and temperature on CO2 production may be underestimated basing on their single effects. Our results suggest that <0.1 mm is a threshold value of biochar particle size that is helpful to soil carbon sequestration.