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Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2 enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2 (EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change. [ABSTRACT FROM AUTHOR]

Current water-nitrogen (N) management strategies are necessary to be improved to increase crop productivity while reducing environmental costs. However, the effects of improved water-N management strategies on paddy CH 4 and N 2 O emissions simultaneously generated during the growing and non-growing seasons have not been explored. Therefore, in this study, four water-N management practices—urea plus conventional irrigation (UREA+CI), urea plus alternate wetting-drying irrigation (UREA+AWD), controlled-release N fertilizer plus CI (CRNF+CI), and CRNF plus AWD (CRNF+AWD)—were evaluated in a 3-year field experiment following a randomized complete block design with three replications each. The results demonstrated that during rice growing seasons, CH 4 emissions significantly decreased by 12.6–44.9% under UREA+AWD and by 17.2–32.1% under CRNF+CI, compared to UREA+CI, respectively, and CRNF+SWD showed the highest mitigation potential. N 2 O emissions were reduced in CRNF treatments (CRNF+CI and CRNF+AWD) but increased by replacing CI with AWD during rice growing seasons, suggesting the potential effects of water regimes on N 2 O emissions. Furthermore, AWD and CRNF reduced CH 4 emissions during the land preparation period before the late rice growing season and the fallow period, whereas CRNF treatments triggered the release of N 2 O in the fallow period. Moreover, there were no significant differences in soil organic carbon sequestration rates among the treatments. The results indicated that AWD, CRNF and their combination significantly reduced annual net total greenhouse gas emissions without yield loss. Collectively, this study unravels the potential of alternative water-N management strategies to improve rice yields while minimizing GHG emissions in double rice cropping systems. • AWD, CRNF and their combination significantly reduced CH 4 emissions. • CRNF had opposite effects on N 2 O emissions in growing and non-growing seasons. • CRNF promoted annual N 2 O emissions. • AWD-CRNF combined practices minimized GHGI. [ABSTRACT FROM AUTHOR]

The combined impacts of modified nitrogen (N) fertilizers and water saving irrigation (WSI) on greenhouse gas (GHG) emissions and grain yield of rice paddies have not previously been documented. GHG emissions from rice paddies under modified N fertilizers and WSI deserve attention because water and N are being used extensively to attain higher grain yield. A field experiment was conducted to evaluate the influence of modified N fertilizers and WSI on methane (CH 4 ) and nitrous oxide (N 2 O) emissions and grain yield in rice paddies. Four treatments were applied: urea with conventional irrigation (U + CI), urea with shallow water depth with alternate wetting-drying water saving irrigation (U + SWD), polymer-coated controlled release urea with SWD (CRU + SWD), and nitrapyrin-urea composition plus hydroquinone with SWD (NU + HQ + SWD). Compared to U + CI, CH 4 emissions significantly decreased by 26% and 31%, and N 2 O emissions increased by 52% and 42% under U + SWD in the early and late rice growing seasons respectively (p < 0.05). Although SWD increased N 2 O emissions, total GHG emissions (T GHG ) reduced by 20% and 25% in the two rice seasons under U + SWD, and GHG emission intensity (GHGI) decreased by 24% on average. Modified N fertilizer applications also affected grain yield and GHG emissions under SWD. Compared with U + SWD, CRU + SWD and NU + HQ + SWD reduced CH 4 , N 2 O emissions and T GHG by 28–49%, 12–44% and 26–45%, respectively, while grain yield increased by 6–35%. Reduction in CH 4 emissions occurred because, compared to urea, CRU and NU + HQ can inhibit CH 4 production and transport by controlling development of invalid tillers, while their nitrogen release patterns were more favorable for CH 4 consumption. In summary, modified N fertilizers in combination with SWD are a win-win strategy to improve grain production while reducing GHG emissions in the rice cropping system. [ABSTRACT FROM AUTHOR]

Crop residue-based bioenergy (CRB) is a green replacement for fossil fuels and an effective way of utilizing crop residues. Understanding CRB's GHG reduction effects is critical for predicting its contributions to carbon neutrality. However, many studies have focused on single products or regional assessments, and results remain uncertain and lacking in systematic examination of the diversity in products, feedstock types and their supply. Therefore, this paper systematically investigates the GHG reduction efficiency, driving factors and abatement costs of principal CRB products using a database of 225 cases composed of 71 carbon trading projects and 154 projects analyzed in scientific publications. The results show that bio-power and/or heat (bio-P&H) is highly efficient (689 kg CO 2 e/t dry CR) and economical (269 $/t CO 2 e) in reducing GHG emissions, but liquid biofuels is not encouraged because of its inefficient performance. Plant size and feedstock collection radius significantly affected GHG reductions of bio-P&H and liquid biofuel. Recommended plant sizes and feedstock types for CRB production were identified from environmental and economic perspectives. Overall, these results clarify the patterns and driving factors of GHG reduction efficiency and abatement costs of various CRB products, providing a framework for optimizing CRB development to combat climate change. [Display omitted] • AsSessing GHG reduction patterns of various crop residue-based bioenergy products. • Comprehensive assessment of the environmental and economic performance. • Identifying the impacts of key factors influencing GHG reduction efficiency. • A meta-analysis based on both scientific publications and project datasets. • Bio-power & Heat shows good GHG reduction efficiency with lower abatement cost. [ABSTRACT FROM AUTHOR]

To evaluate long-term effect of biochar application on yield-scaled greenhouse gas emissions (YSGE) in a paddy rice cropping system, a 4-year field experiment by static chamber - gas chromatograph method was conducted in South China. Principal component analysis and terminal restriction fragment length polymorphism (T-RFLP) and real-time qPCR was used to unravel the microbial mechanisms of biochar addition. Six treatments were included: control (CK), application of 5 t ha − 1 biochar (BC1), application of 10 t ha − 1 biochar (BC2), application of 10 t ha − 1 biochar (BC3), rice straw return at 2400 kg ha − 1 (RS) and inoculated rice straw return at 2400 kg ha − 1 (RI). The results indicated that biochar amendment significantly decreased methane (CH 4 ) and gross greenhouse gas (GHG) emissions. This may primarily be ascribed to the stimulated biodiversity and abundance of methanotrophic microbes, increased soil pH and improved aeration by reducing bulk density after biochar incorporation. Compared with CK, RS and RI, 26.18%, 70.02%, 66.47% of CH 4 flux and 26.14%, 70.16%, 66.46% of gross GHG emissions were reduced by biochar (mean of three biochar treatments), respectively. Furthermore, biochar significantly increased harvest index of double rice production ( p < 0.05). In comparison with CK, RS and RI, 29.14%, 68.04%, 62.28% of YSGE was reduced by biochar, respectively, and the highest biochar addition rate (20 t ha − 1 ) contributed most to the mitigation of GHG emissions (36.24% decrease compared to CK) and improvement of rice yield (7.65% increase compared to CK). Results of our study suggested that long-term application of biochar should be the potential way to mitigate GHGs emissions and simultaneously improve rice productivity in the paddy rice system. [ABSTRACT FROM AUTHOR]

Practical nitrogen fertilizers are required that simultaneously increase yield and reduce greenhouse gas (GHG) emissions from rice ( Oryza sativa L.) paddies. A field experiment was conducted to measure methane (CH 4 ) and nitrous oxide (N 2 O) fluxes in situ during two double rice-winter fallow rotations (2012–2014) under five different nitrogen fertilizer treatments: traditional urea (CK), polymer-coated controlled release urea (CRU), urea with N-Sever nitrapyrin (NU), urea with 3,4-dimethylpyrazole phosphate (DMPP), and urea with effective microorganisms (EM). The results revealed that GHG emissions ranged between 77.2 and 178.2 kg CH 4 ha −1 and 4.18 and 10.11 kg N 2 O ha −1 averagely over the whole rotation, and significant differences ( P < 0.05) among treatments and seasons were found. N 2 O emissions accounted for 26.6–36.9% of total GWP, and significant N 2 O emissions were observed during the winter fallow period, ranging from 3.1 to 3.88 kg N 2 O ha −1 . Compared to the GWP (7.66 and 8.85 Mg CO 2 ha −1 ) and GHGI (0.52 and 0.63 Mg CO 2 Mg −1 grain) from CK in 2012 and 2013 rotation, respectively, CRU achieved the highest reduction (48.5% for GWP and 55.4% for GHGI) in 2012, NU achieved the highest reduction (37.6% for GWP and 43.1% for GHGI) in 2013, and other treatments also realized different levels of decrease. Thus, controlled release urea, nitrification inhibitor or effective microorganisms might be effective fertilization options for low-carbon rice production with high yield. [ABSTRACT FROM AUTHOR]

Rice cultivar is the most influential factor affecting methane emissions from double rice fields. A two-year field experiment was conducted at Huizhou, Guangdong province, South China, to identify from among nine cultivars those cultivars with high-yield potential and lower yield-scaled methane emissions (YSMEs). Methane emissions were measured using the static chamber – gas chromatograph method. Results indicate that the cultivars Qihuazhan (QH), Yexianzhan 8 (YX8) and Yue’erzhan (YE) provide higher rice grain yield (8.69%) with lower YSME (30.27%) compared to the other six cultivars (Yexianzhan 6, Yuejingsimiao, Hefengzhan, Huangsizhan, Huangruanzhan and Huangxiuzhan) (p < 0.05). In particular, QH has the highest yield potential (6777 kg ha−1) and lowest methane emission intensity (0.36 kg kg−1yield) capacity. Methane emissions from the double rice field was found to be significantly (p < 0.05) and positively correlated with tiller number, culm biomass and soil organic matter, dissolved soil organic carbon and total carbon content, but negatively correlated (p < 0.05) with rice harvest index (HI), and root and panicle biomass, suggesting that organic source strength provides the substrate of methane production while the oxidation potential in the rhizosphere and the methane transport capacity of rice roots and culm dominate the emissions of methane from soil to the atmosphere. Multivariate decision regression tree (DRT) analysis showed a significant class difference between QH, YX8 and YE with the other six cultivars. These three cultivars are suitable for promotion of low carbon agriculture in South China. DRT analysis also successfully illustrated a potential way to identify rice varieties for low YSME by decisive parameters of tiller number (<15), HI (>0.43) and nitrogen assimilation of leaves (<40). These findings suggest that optimization of rice cultivars may represent an effective way to address both food demand and climate change concerns by improving rice yields while simultaneously minimizing the impact of climate change per unit yield. [ABSTRACT FROM AUTHOR]

The resource utilization of organic materials in China cropland is a great challenge we are facing now. To study the ecological effects of biochar utilization, and explore the response of carbon emission intensity (GHGI) to biochar amendment for the long term in a double rice field in South China, two-year field measurements of greenhouse gases based on a static chamber-gas chromatography method were conducted. Six experimental treatments were set up, including 1) CK (famer traditional operation), 2) BC1 (biochar amendment at 5 t/hm2), 3) BC2 (biochar amendment at 10 t/hm2), 4) BC3 (biochar amendment at 20 t/hm2), 5) RS (raw rice straw residue return) and 6) RI (composted rice straw residue return). As a result, compared to CK, all of the biochar treatments inhibited the emission peaks of greenhouse gases from the double rice field. During the four rice growing seasons, the three biochar treatments decreased the 100 yr-scaled carbon dioxide emission equivalents by 27.53%, 58.65%, and 63.43%, respectively, compared with CK, RS, and RI. The biochar treatments significantly reduced methane emissions (P<0.05) at an average reduction rate of 50.84%. Among the three biochar and two rice straw residue treatments, BC3 had the lowest methane emission potential (2.75 mg/(m2 h)), while RS had the highest (10.05 mg/(m2·h)). For the nitrous oxide emissions, the average value of the three biochar treatments was lower than CK but higher than the two rice straw residue return treatments (P>0.05). Furthermore, there was no statistical significant yield increase effect found in the biochar treatments (P>0.05), compared with CK, RS, and RI, as the four-season average rice yields of the three biochar treatments were increased by 3.21%, 5.11%, and 2.29%, respectively. A significant higher yield in BC3 was observed than that in RS (P<0.05). Additionally, on a 100-year horizon, the GHGI of the three biochar treatments (average at 0.33 kg/kg) were 30.57%, 61.00%, and 64.82% lower than CK (0.48 kg/kg), RS (0.86 kg/kg), and RI (0.48 kg/kg), respectively. By the correlation matrix and principal component analysis, the biochar amendment controlled the distribution of rice yield, harvest index, soil organic matter, total carbon content, and chlorophyll content, while the rice straw residue return treatments dominated the distribution of the methane flux and GHGI. In summary, based on the present study, the application of the regression tree analysis offered a quantitative alternative to decision-making in analyzing the effects of biochar amendment on ecological environment. The results of this study indicated that the biochar amendment in soils has the potential to enhance soil carbon sequestration, increase rice yield, and mitigate the carbon emission intensity and the impact of climate change by optimization of the field managements and biochar return in an appropriate amount. This research could be used as a successful case study of scientific utilization of crop straw residue in China's agriculture. [ABSTRACT FROM AUTHOR]

Maize production inevitably generates greenhouse gas (GHG) emissions which contribute to global warming. The greenhouse gas intensity (GHGI) of maize production was controlled by various management techniques. Fuel, fertilizer production, herbicide production, seed consumption, transportation, and on-farm energy consumption all result in GHG emissions. Life cycle assessment (LCA) methodology was adopted in this study to calculate GHG emissions under different fertilization treatments aiming at comprehensively evaluating the effects of different fertilization treatments on GHG emissions and selecting the options with both economic benefits and GHG mitigation. Four different fertilization treatments are: local traditional fertilization; urea treatment; sulfur coated urea; and urea added with dicyandiamide treatment. Static chamber and gas chromatography (GC) systems were used to continuously monitor N2O emissions from maize cropland. N2O emissions under different fertilization treatments were calculated. Data on the amount and type of fertilizer applied, energy consumption for the tillage, herbicide consumption, irrigation area and Diesel consumption, for tillage, electricity consumption for irrigation, and seed consumption were collected. Total GHG emissions from fertilizer production, energy consumption, seed production were estimated. GHG emission intensity based on grain yield and economic benefit were also calculated. The result showed that N2O emissions from fertilization, total GHG emission of the whole life cycle, emission intensities based on yield and output were all ranked as local traditional fertilization>urea treatment>urea added with dicyandiamide treatment>sulfur coated urea treatment. N2O emissions from the local traditional fertilization treatment was very significantly higher than that from the other three treatments (P<0.01). N2O emissions from the sulfur coated urea treatment was significantly lower than that from the urea treatment (P<0.05) and was not significantly different from that in the urea added with dicyandiamide treatment (P>0.05). Total GHG emissions from the treatments of local traditional fertilization, urea, sulfur coated urea, and urea added with dicyandiamide were 4.11, 2.71, 2.56, and 2.61 t/(hm2.a) respectively. Emission per unit of yield for the treatments of local traditional fertilization, urea, sulfur coated urea, and urea added with dicyandiamide were 364.1, 238.3, 216.6, and 223.4 kg/t maize, respectively. Emission per 10 000 yuan for the treatments of local traditional fertilization, urea, sulfur coated urea, and urea added with dicyandiamide were 2.19, 1.32, 1.15, and 1.18 t /10 000 yuan respectively. Compared with a traditional fertilization treatment, sulfur coated urea could reduce total GHG emissions, GHG emission per unit of yield and per 10 000 yuan net output by 37.8%, 40.5%, and 47.3% respectively, while the urea added with dicyandiamide treatment could reduce total GHG emissions, GHG emission per unit of yield, and per 10 000 yuan by 36.5%, 38.6%, and 45.9% respectively. Production of fertilizers, especially nitrogen fertilizer, makes the greatest contribution to total GHG emissions for maize cultivation, accounting for 42.4%-55.0% of the total GHG emissions from the four treatments, followed by fertilizer application, accounting for 20.8%-26.1% of the total GHG emissions from the four treatments. In order to ensure grain output and economic benefits, two fertilization treatments, sulfur coated urea treatment and urea added with dicyandiamide treatment, resulted in relatively low total emissions and emission intensity. They can be recommended as options to mitigate GHG emissions from maize production. [ABSTRACT FROM AUTHOR]

Greenhouse gas intensity (GHGI) (methane and nitrous oxide) of double rice paddy was controlled by various field managements, tillage, and rice straw return to the field. On one hand, the choice of the tillage mode affects the gas permeability of soil during the crop-growing stage. On the other, the incorporation of rice straw can be a critical way to amend the loss of soil carbon. Both of the two practices have their advantages and disadvantages on rice production and environmental effects. In fact, no tillage causes less methane emissions from double rice fields than the field with conventional tillage. Nevertheless, rice straw return to the field increases tremendous methane production and emission of organic carbon. In spite of its promotion on rice productivity and sequestration of soil organic carbon pool, this practice is still under discussion .Therefore, multi-management mode should be considered simultaneously when regional or national policy is made to reduce GHGI from agriculture. To date, the study of the interaction effect of tillage and the rice residue return on GHGI from double rice fields is lacking. Most of the previous studies focused only on one field management and its influence mechanism. Consequently, we conducted a measurement for 4 rice growing seasons on GHGI of a double rice field in Hunan, China to investigate the interaction effect of tillage and rice straw return on both the social-economical and environmental benefits. The improved static chamber-GC (gas chromatography) method was used to monitor the greenhouse gas emissions from the rice paddy. Major improvements made on the chamber include the adjustable sampling tube and the pores in the base. The former was designed to change with the growth of the rice plant and the latter favored the communication of soil water between the inside and outside of the base. Both of them enhanced the accuracy of the field measurement. Four field practices were included in this research, viz. CWS (Conventional tillage, without straw residue return), NWS (No till, without straw residue return), HN (High stubble residue retain, no till), and HC (High stubble residue retain, conventional tillage). Results showed that there is a significant interaction effect of tillage and rice residue return on methane emissions (P<0.05) instead of nitrous oxide emissions from the double rice field. The interaction effect has pronounced seasonal and inter-annual variation. By the seasonal average value, the sequence of methane flux of each treatment is the following: HC>HN>CWS>NWS (HC significantly greater than HN while no significant difference between HN and CWS). Similarly, the amount of rice grain yield of each treatment of the 4 seasons is the following: CWS>HN>HC>NWS (no significant difference between HN and CWS). For the GHGI, the following order is disclosed: HC>CWS>HN>NWS (HN less than HC and CWS significantly, P<0.05). This indicated that compared to CWS, "no-till plus high stubble residue (HN)" offset the stimulations of conventional tillage on methane production and emission while simultaneously promoting the rice grain yield. Thus the multimanagement mode mitigated the GHGI of the double rice field significantly. Under the requirement of organic tillage and the sequestration of agricultural soil carbon pool, HN mode should be considered of great importance. This study can provide scientific support on the measurement choice of greenhouse gases effect reduction from the major rice production region of China. [ABSTRACT FROM AUTHOR]

Highlights: [•] The cost-effectiveness of water-saving irrigation based climate change mitigation was researched. [•] The cost-effectiveness of water-saving irrigation based climate change adaptation was researched. [•] The mitigation and adaptation potential in the coming decade was researched. [•] Development proposal of water-saving irrigation was made according to cost-effectiveness analysis. [ABSTRACT FROM AUTHOR]

Methane is produced in anaerobic environments by obligate anaerobic microorganisms through the decomposition of organic matters. To investigate the regression relationships between methane emissions and soil microbes in a double-rice paddy under various field practices, a two-year study was conducted to investigate the seasonal variation of methane emissions and the total activities of soil microbes (TASM) as well as the populations of methanogens (PMET) using the static closed-chamber-GC (gas chromatography) and the most probable number methods. Seven management practices were included in this study to look at the average effect of field treatments on methane emissions and TASM as well as PMET,viz. CWS (conventional tillage + without straw residues + urea), NWS (no tillage + without straw residues + urea), SCU (conventional tillage + without straw residues + controlled-release urea), HN (high stubbles + no tillage + urea), HC (high stubbles + conventional tillage + urea), SN (straw cover + no tillage + urea) and SNF (straw cover + no tillage + urea + continuous flooding). The daily average values of methane emissions and TASM as well as PMET from seven treatments were used for the analysis. Regression analysis was conducted using the R statistical software. Different field practices have significant effect on methane flux and TASM and PMET and similar seasonal variations of methane flux and TASM as well as PMET were found during the rice-growing seasons. Pronounced positive correlations between methane flux and TASM, and PMET were observed. Such relationships can be well described by the exponential or quadratic polynomial models, respectively. Regression analysis indicated that PMET could explain individually at least 97% of variance of methane flux (R2 = 0.97,P < 0.001), while the fitting precision of multiple nonlinear regression model for methane flux with two predictors of TASM and PMET was slightly higher than the univariate regression analysis (R2 = 0.98,P < 0.001). However, as we know, methane emissions from paddy soils are affected by many factors, of which TASM and PMET are the most direct influential variants. In order to reasonably reveal the interactions between methane emissions and environmental factors, the multivariate nonlinear regression analysis should be carried out based on data derived from the extensive field experiments rather than few laboratory trials. [ABSTRACT FROM AUTHOR]

Soil nitrification is a crucial process that increases nitrogen (N) availability for plants and drives nitrous oxide (N 2 O) emissions and nitrate (NO 3 −) leaching. Ongoing climate warming and elevated CO 2 in the atmosphere may affect nitrification in opposite directions. However, their interactions are not known, especially in the long-term and in flooded conditions common in paddy soils. We conducted a long-term (9 years) field experiment with simultaneous manipulation of temperature (+2 °C above ambient) and CO 2 (+60–100 ppm above ambient) to evaluate the impacts of warming and CO 2 enrichment on the community structure, diversity, and population size of ammonia-oxidizing archaea (AOA) and bacteria (AOB), soil nitrification and physico-chemical characteristics. Elevated CO 2 increased soil organic carbon (SOC) content (18%), microbial biomass N (65%), and carbon (27%). These changes accompanied an increment in AOB functional-gene abundance (181%) and soil nitrification rate (96%). Elevated temperature also increased (58%) soil nitrification rate. The combination of warming and CO 2 enrichment enhanced AOB gene abundance (232%) and nitrification rate (133%). Impacts of these climate change factors on nitrification strongly depended on AOB gene abundance and microbial biomass, but not on AOA abundance. Higher root C inputs by rhizodeposition and pH under these climate change factors explained the substantial increases in AOB gene abundance, as nutrient-rich and alkaline soils favor AOB growth. By contrast, the AOA community was less sensitive to these climate change factors. Community composition, diversity, and richness of nitrifiers were remarkably resilient in response to individual and interactive impacts of warming and elevated CO 2. Consequently, climate change will increase AOB population size but without community restructuring and will increase nitrification in paddy soils, which enhances N availability with consequences for crop productivity, N 2 O emissions, and NO 3 − leaching. [Display omitted] • Nitrifier community structure remained stable under elevated CO 2 and temperature. • Elevated CO 2 and temperature alone and in combination increased nitrification rate. • Effects of elevated temperature on nitrifier gene abundance were not significant. • Ammonia-oxidizing bacteria (AOB) were mainly responsible for nitrification in paddy soil. • Ammonia-oxidizing archaea were less sensitive to elevated CO 2 and temperature than AOB. [ABSTRACT FROM AUTHOR]

China's green development has advanced national strategic requirements for excessive nitrogen application, greenhouse gas emission reduction, and efficient production in food systems. However, large challenges still exist in achieving these goals. In this study, a comprehensive meta-analysis and random forest identification were conducted to integrate nitrogen fertilization based nitrous oxide (N 2 O) emission data from field experiments in the dry farming system of China (DFSC), and to analyze the dependency of N 2 O emissions and crop yield on nitrogen inputs. We then quantified the potential reasonable nitrogen dose in the DFSC that would simultaneously reduce N 2 O emissions and favor China's green development. The results showed an absolute impact of nitrogen input on N 2 O emissions, and a significant nonlinear response between N 2 O emissions and nitrogen dose in the DFSC. However, the crop yield exhibited a different pattern: yields of cereal and cash crops in response to nitrogen input were modeled by a quadratic polynomial, especially at extremely high nitrogen rates (>300 kg N ha−1 for cereals and >600 kg N ha−1 for cash crops). The yield enhancing effect tended to be flat or even decrease. We propose to achieve a reasonable nitrogen dose by reducing the 1/3 nitrogen surplus in the DFSC, according to the various soil-climatic conditions. For cereal, cash, vegetable, tea and orchard crops, the values should be 98.72 – 133.46, 67.66 – 107.4, 258.53 – 470.57, 159.61–296.09 and 269.08–383.48 kg N ha−1, respectively. The findings of our investigation indicate that implementation of a reasonable nitrogen dosage will not give rise to a large yield decrease and will better contribute to meeting the requirements of N 2 O mitigation and a national green development strategy. • Nonlinear response of N 2 O emissions to N input exist in DFSC. • Crop yield in DFSC exhibited Quadratic polynomial correspondence to N application. • Reducing N 2 O emissions by abatement N use favors both food security and green development in China. [ABSTRACT FROM AUTHOR]

Our understanding on how soil organic carbon (SOC) storage, crop yield, and yield stability are influenced by climate is limited. To critically examine this, the impact of long-term (≥10 years) application of nutrient management practices on SOC storage, crop productivity, and yield stability were evaluated under different climatic conditions in China using a meta-analysis approach. The cropping area of China was divided into four distinct groups based on local climatic conditions (warm dry, DW; warm moist, WM; cool dry, CD; cool moist, CM). Results indicated that the impact of nutrient management practices on SOC storage, crop yield, and yield stability varies under different climatic zone in China. The use of unbalanced mineral fertilizer (UMF), and balanced mineral fertilizer (BMF) led to a loss in SOC storage by 6%, and 11% under CM climatic zone and gains in DW, WM, and CD climates. Organic fertilizers (OF), combined unbalanced mineral and organic fertilizers (UMOF), and combined balanced mineral and organic fertilizers (BMOF) were able to sustain and enhance SOC storage under all climatic conditions. However, the largest increase in SOC storage across all climates was seen for BMOF. Further, corresponding values of crop productivity and yield stability were also highest for BMOF among all the nutrient management treatments. A linear-plateau model indicated that maximal yield responsive SOC stock (C opt) levels ranged from 33.43 to 45.51 Mg C ha−1 for rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum) production. To enhance and sustain SOC storage, and crop productivity of croplands under different climates, BMOF appears to be the most appropriate nutrient management strategy. Our findings demonstrate that it is essential to optimize nutrient management strategies according to the local climate to protect soil from SOC losses, and for achieving sustainable crop production. • The impact of nutrient managements on SOC storage, crop yield, and yield stability varies under different climatic zones. • Unbalanced mineral, and balanced mineral fertilizer led to a loss in SOC storage by 6%, and 11% under cool moist climate. • Combined balanced mineral with organic inputs is crucial for maximal SOC storage and crop yields under different climates. • Maximal yield responsive SOC stock levels ranged from 33.43 to 45.51 Mg C ha−1 for rice, maize, and wheat production. [ABSTRACT FROM AUTHOR]

• Three isotopic methodologies were used to quantify the biogenic CH 4 production pathway. • AM processes predominant the CH 4 production in the agricultural river network. • Long-term measurements provide the new understanding of atmospheric CH 4. Methane (CH 4) emitted from river networks provides a globally significant, yet poorly constrained barrier for the refinement of national greenhouse gas (GHG) inventories and the global CH 4 budget. This study employed three isotopic methodologies, i.e., a simple mixing model, apparent fractionation factor, and dual isotopes (δ13C−CH 4 and δD−CH 4) to identify the biogenic CH 4 production pathway (BMPP) in a typical agricultural river network in subtropical China. The results indicated that the contribution of acetoclastic methanogenesis (AM) to BMPP in the Tuojia River network (TRN) ranged from 85 to 99%, with the first reach (S1) supporting the most biogenic CH 4 production. Furthermore, the α C value ranged from 1.00 to 1.039 and increased spatially over the four reaches (S1 to S4), while the α D value varied from 1.393 to 1.394, with S1 having the lowest value. The dual isotopes of δ13C and δD reflected a mixed BMPP. Clearly, the isotopic composition of CH 4 corroborated the predominance of AM in the BMPP in the TRN. Additionally, there was a remarkable spatiotemporal variation in δ13C−CH 4 and δD−CH 4 , as well as α C and α D. In combination with the correlation between the two paired isotopic signatures (antipathetic and positive, p < 0.05, respectively), this suggested a change in the BMPP in the TRN. The findings of our study implied that there was great impact of agricultural production and residential activities on environmental behavior of stable isotopes. Consequently, we recommend that multiple isotopic measures, based on long-term in situ isotopologue monitoring, should be applied when the uncertainties of CH 4 emissions from river networks are addressed. [ABSTRACT FROM AUTHOR]

River networks in subtropical agricultural hilly region become an inconvenient greenhouse gas (GHG, methane and nitrous oxide) source because of the influence of human activities, which has caused large uncertainties for refinement of national GHG inventories and their global budget. Based on field monitoring experiments at high temporal resolution, we employed regression tree and importance analysis to identify quantitatively factors that influence the diffusive flux of GHGs to provide a scientific basis for reducing GHG emissions and controlling regional carbon and nitrogen losses. The results indicate that significant spatiotemporal variation of methane (CH 4) nitrous oxide (N 2 O) diffusion occurs in all the four reaches (W1, W2, W3 and W4) of Tuojia river networks. Among them, W1 contributed lowest CH 4 (22.55 μg C m−2 h−1) and N 2 O (5.00 μg N m−2 h−1) diffusive flux than the other three (P < 0.05), while W4 offered highest CH 4 (166.15 μg C m−2 h−1) and N 2 O (30.47 μg N m−2 h−1) diffusive flux but with no statistically significant difference between W2 and W3 due to homogeneous extraneous nutrition loading into the two reaches. W4 also contributed largest cumulative flux of CH 4 (14.55 kg C ha−1 yr−1) and N 2 O (2.69 kg N ha−1 yr−1) in Tuojia River networks (P < 0.05). Furthermore, the regression tree and importance analysis indicate that, in the anaerobic environment, dissolved oxygen saturation controlled the production and diffusion for both CH 4 and N 2 O. The findings of this investigation highlighted that decision support tools provide an effective pathway to enhance the GHG mitigation technology research in agroecosystems and simultaneously shed light on the global campaign on refinement of national GHG inventories as well as regional nutrient management. Unlabelled Image • Higher reach of Tuojia River contributes more GHG diffusive flux. • There is significant impact of farming and living activities on behavior of GHGs transfer. • RTA revealed saturation of dissolved oxygen as most influential factor of GHG diffusion. [ABSTRACT FROM AUTHOR]

Scaling up of farming operations by land use rights transfers has been a growing trend in China in recent years. However, little is known about the implications of this trend for greenhouse gas (GHG) emissions and soil organic carbon (SOC) stock changes. Using farm survey data from Shandong Province, a typical grain production region in China, we used a life cycle assessment (LCA) method to evaluate the impact of different farm scales on input use efficiency, grain production, SOC stock changes and GHG emissions. Large-scale farming operations (LSFO) enhanced input use efficiency by reducing fertilizer and pesticide consumption rates and energy use for irrigation. Compared with small household farming operations (SHFO), LSFO attained higher grain yield in wheat-maize and wheat-rice cropping systems. Compared with small farms, carbon footprints per unit area of large-scale farms were lower for wheat (17%) and maize (28%) in the wheat-maize cropping system and for wheat (14%) and rice (8%) in the wheat-rice cropping system. Moreover, LSFO reduced GHG emissions (7–21%) and enhanced SOC stocks (6–9%), compared with SHFO. This study highlights that in China, land use rights transfers to promote large-scale farming can help achieve cleaner grain production with less negative impact on the environment. [ABSTRACT FROM AUTHOR]

Three kinds of climate change simulation devices are used for study elevated CO2 concentration and air temperature increase: 1)Open system: Free Air CO2 Enrichment (FACE) with Infrared Heating(IH); 2)Half-open system: Open-Top Chamber (OTC); 3)Close system: Environment Chamber(EC). But the extremely high hardware and running cost of FACE and IH are the main restricts for their application. EC system cannot represent the really condition with large extent of crop growth environment change. Traditional OTC system with much lower cost has nearly the same growth condition for crop, but it is a passive temperature increasing system and has no CO2 addition. To well use the advantage of Half-open OTC technique for climate change simulation, we improved the traditional Open-Top Chamber (OTC) device by adding heating module, CO2 injection module and air exchange module. A hexagonal OTC was designed with 1.2m side length and 2.5m height, and the CO2 tank used for CO2 injection source and semiconductor sheet sealed for the heating system. Air heating and CO2 injection were automatically controlled when pumping outside air into OTC by fans to simulate the elevated air temperature and CO2 concentration scenario. We applied the improved OTC in early rice season, and the OTC was emplaced in the real rice paddy field without obstacle at the bottom for water supply. And air temperature, humidity and CO2 concentration were measured by every 2 min. The results showed that the difference of daily mean deviation of air temperature of the controlled OTC and the objective simulation temperature can be controlled less than ±0.2℃ with the largest difference of -0.58℃, and the controlled deviation of CO2 concentration was -39.4~4.8 μL/L. This research indicated that the improved OTC can be applied to simulate the elevated air temperature and CO2 concentration of the future climate change scenario. Meanwhile, the relative humidity in improved OTC is also showed that relative humidity (RH) nearly has no change without temperature increase, and would increase by 2% if air temperature increased. In a word, this improved OTC device can be used to simulate elevated CO2 concentration and air temperature of early rice for climate change simulation research. [ABSTRACT FROM AUTHOR]

Abstract: Although sensitivity analysis (SA) was conducted on the DeNitrification–DeComposition (DNDC) model, a global SA over a long period of time is lacking. We used a method of Bayesian analysis of computer code outputs (BACCO) with the Gaussian emulation machine for sensitivity analysis software (GEM-SA) to conduct a long-term SA of DNDC for predicting the annual change of soil organic carbon (dSOC), nitrous oxide emission (N2O) and grain yield of spring wheat. Twenty seven non-weather input parameters with wide ranges were selected for SA using weather data recorded from Three Hills, Alberta over 86 years (1921–2006). The SA had two steps: 1) a preliminary BACCO GEM-SA was conducted to identify a more accurate emulator sampling method and to screen out parameters with insignificant influence on model outcomes; and 2) final BACCO GEM-SA was conducted with optimal input design set for emulator training runs varying only the significant input parameters. Results indicated that the Maximin Latin Hypercube sampling method outperformed the LP-τ method with higher emulator accuracy. Most of the 27 input parameters contributed little to the three outputs by the first step BACCO GEM-SA. In the second step of BACCO GEM-SA there were only three (in the case of dSOC) and six (in the cases of N2O and yield) input parameters whose influence contributed to more than 10% of the total output variances by their total effects. Among the selected parameters, initial soil organic carbon and clay content are very important and were important in determining results for all three outputs. Sensitivities of some parameters, such as clay content and urea fertilizer amount changed dramatically over the years. This indicates that a single year SA may overestimate or underestimate a long-term parameter effect on the model prediction. The two-step procedure with the BACCO GEM-SA method improved the accuracy of SA and provided important information for model validation and parameterization. [Copyright &y& Elsevier]

Elevated atmospheric temperature and CO 2 concentration ([CO 2 ]) can strongly affect yield, CH 4 and N 2 O emissions in rice paddies. However, understanding of their response to combined temperature and [CO 2 ] increases under field conditions is still limited. To study this issue further, an open-top chamber (OTC) platform was set up to simulate two levels of atmospheric temperature (ambient and 2 °C elevated) and two levels of [CO 2 ] (ambient and 60 ppm elevated) during two rotations of double rice, including twelve independent OTCs and three un-chambered open field sites as trial plots. The experimental site is located in Hubei Province, Central China, which has a subtropical monsoon climate. In all four rice seasons, elevated CO 2 induced an increment in grain yield by 11.4–19.7%, while also enhancing CH 4 and N 2 O emissions by 19.8–52.6% and 102.4–140.0%, respectively, compared with ambient temperature and [CO 2 ]. Elevated temperature enhanced CH 4 emissions by 4.4–36.0%, and decreased N 2 O emissions by 1.5–10.5% in three rice seasons. Elevated temperature had different effects on grain yield, with a reduction of 1.0–3.2% in early rice and an increase of 6.3–9.2% in late rice. When elevated temperature and [CO 2 ] were combined, there was a positive interaction that further enhanced CH 4 emissions and yield of late rice, and an offsetting effect on N 2 O emissions and yield of early rice. Over the 2-year experiment, warming and CO 2 enrichment caused an increase of 9.3–44.2% in greenhouse gas intensity, suggesting that more greenhouse gas emissions will be emitted to produce a unit mass of rice under projected global warming. These findings provide initial data for the estimation of CH 4 and N 2 O emissions under elevated temperature and [CO 2 ] in double rice cropping system, and stress the need for effective management practices that promote rice yield while reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

• Increase of SOC, DOC, and SMBC in the rhizosphere reached up to 7.0%, 34.6%, and 26.1% across global agroecosystem. • Environmental variables significantly affected rhizospheric SOC and DOC, not for SMBC. • Soil microbial structure, diversity, and function were not critical for regulating rhizospheric carbon. • Dominant factor regulating the rhizosphere effect on SOC and DOC was abiotic rather than biotic factors. The carbon (C) that surrounds the rhizosphere serves as the nexus between soil, plants, and atmosphere. Although it is known that rhizospheric C is sensitive to soil management and environmental changes, the influences of crop roots on rhizospheric C across global agroecosystems have not yet been systematically quantified, which limits our understanding of the terrestrial C cycle. A comprehensive meta-analysis including 748, 294, and 695 paired data of soil organic carbon (SOC), dissolved organic carbon (DOC), and soil microbial biomass carbon (SMBC) in rhizosphere and corresponding bulk soil from 154 papers, together with 25 biotic and abiotic variables, was conducted to quantify the effects of the rhizosphere on soil carbon across global agroecosystems. We found that the rhizosphere had greater SOC, DOC, and SMBC compared to the bulk soil, with 7.0%, 34.6%, and 26.1%, respectively. Rhizospheric effects on SOC and DOC varied significantly with different climate zones, aridity indices, and crop types; however, this phenomenon did not occur with SMBC. Soil available nutrients were the main driving factor behind rhizospheric SOC (relative influence of 37.0%), whereas SMBC played a small role in regulating the rhizosphere DOC, aside from the aridity index, crop type, initial soil C, and soil pH. The soil microbial structure, diversity, and function were not critical for regulating rhizospheric C. Path analysis revealed an intercorrelated network involving climate, physicochemical soil properties, and SMBC to determine the rhizospheric impacts on SOC and DOC. Understanding the size and driving factors of the rhizospheric effects on soil C is useful for determining how crop selection might affect broader C and nutrient cycling in agroecosystems. [ABSTRACT FROM AUTHOR]

Sustainable production of paddy rice is essential in supplying staple food worldwide. In the present study, we determined annual yield, greenhouse gas emissions (GHGs) and carbon footprint of double cropping paddy rice (Oryza sativa L.) as impacted by organic and inorganic amendments in a 38-year study from central China. A balanced synthetic fertilizer of nitrogen (N), phosphorus (P) and potassium (K) combined with rice straw application (NPK_RS) consistently produced higher annual grain yield by 5%, 11% and 64%, respectively, compared with NPK, anaerobically digested manure (NKM) and NK. Average GHGs associated with both early- and late-season rice production were 47,300 kg CO 2 eq ha-1 yr-1 for the NPK_RS, 24,100 kg CO 2 eq ha-1 yr-1 for the NPK, 27,700 kg CO 2 eq ha-1 yr-1 for the NKM, 24,300 kg CO 2 eq ha-1 yr-1 for the NK, and 20,400 kg CO 2 eq ha-1 yr-1 for the non-fertilized control (CK). Of the total GHGs, approximately from 80% to 95% of the emissions resulted from methane fluxes, and from 3% to 7% emitted as soil nitrous oxide while only from 2% to 15% of the total emissions derived from other sources such as fertilizer, herbicide and pesticide production and field operation. As a result, carbon footprint of paddy rice varied from 2.1 to 3.9 kg CO 2 eq kg-1 grain. Straw addition with the NPK improved rice yield only marginally, but increased methane emissions and carbon footprint significantly, compared with the NPK. On the other hand, the NKM increased rice yield by 48% and GHGs by 10% and lowered carbon footprint by 23%, compared with the NK. Timing of straw application and manure amendments are critical for improving yield of paddy rice, reducing GHGs, and lowering carbon footprint. [Display omitted] • Manure application effectively eliminates soil phosphorus deficiency. • Balanced chemical fertilizers sustain high yield of double cropping paddies. • Manure and straw addition increase methane emissions. • Straw addition improves rice yield marginally and increases carbon footprint. [ABSTRACT FROM AUTHOR]

• In the early years of adoption, no-tillage (NT) increased surface SOC and reduced it in deeper layers. • NT-driven SOC losses diminished over time and the net change was approaching zero at 14 years. • Annual precipitation and initial SOC were the most influential variables on the effect of NT on SOC. Improved management of agricultural soils plays a critical role in mitigating climate change. We studied the temporal effects of the adoption of no-tillage (NT) management, often touted as an important carbon sequestration strategy, on soil organic carbon (SOC) storage in surface and subsurface soil layers by performing a meta-analysis of 1061 pairs of published experimental data comparing NT and conventional tillage (CT). In the early years of adoption, NT increased surface (0–10 cm) SOC storage compared to CT but reduced it in deeper layers leading to a decrease of SOC in the entire soil profile. These NT-driven SOC losses diminished over time and the net change was approaching zero at 14 years. Our findings demonstrate that NT is not a simple guaranteed solution for drawing down atmospheric CO 2 and regenerating the lost SOC in cropping soils globally and highlight the importance of long-term NT for the recovery of initial SOC losses. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic carbon (SOC) is an important carbon pool which can ameliorate the increasing concentration of atmospheric carbon dioxide as part of the carbon cycling process. Organic carbon in cropland soils is an active pool which is strongly influenced by anthropogenic activities. SOC in cropland soils accounted for 14.5% of the total organic carbon stock of 89.61Mt C in China. In this study, RothC model was used to simulate the change of SOC in upland soils at 626 original 50km×50km grids under B2 and A2 climate scenarios during the upcoming decades in China. Future climate data under B2 and A2 scenarios were predicted by Providing Regional Climates for Impacts Studies (PRECIS) regional climate model downscaled based on HadCM3. The simulation results showed that SOC will generally decrease during the next decades and the decrease rate of SOC will be higher over time if there is no addition of organic material (e.g. organic manure application or straw return) adopted in China. Simulations got the following results: (i) SOC will decrease in most areas of China, especially in northern China; the increase of SOC only occurred in a few scattered grids in Southwest China and mid-south China. The decrease rate of SOC in northern China was higher than in southern China under either B2 or A2 climate scenarios. (ii) The changing rate of SOC over time under B2 scenario was minor during the early 21st century and quite large during the late 21st century. In contrast, the changing rate of SOC over time under A2 scenario was somewhat constant over time. The percentage decrease (decrease rate divided by its basic value in 1980s) of SOC in northern China was around 5.5%, 12%, and 15% by the year 2020, 2050, and 2080 under B2 and A2 scenarios, while it was about 2.3%, 7.7%, and 10.9% under B2 scenario and 3.3%, 4.5%, and 5.5% under A2 scenario in southern China. (iii) Upland soils would lose organic carbon by 2.7tC/ha, 6.0tC/ha, and 7.8tC/ha at the 0–30cm depth by the year 2020, 2050, and 2080, respectively, under the typical conventional tillage without organic material amendment under B2 scenario in China, which accounted for about 4.2%, 9.3%, and 12.1%, respectively, of the basic SOC of 1980s in the upland soils. SOC would decrease by 2.9tC/ha, 6.8tC/ha, and 8.2tC/ha by the year 2020, 2050, and 2080, respectively, under A2 scenario in China, which accounted for about 4.5%, 10.5%, and 12.7%, respectively, of that in 1980s under the conventional tillage and management practices. (iv) Our simulations of future change in SOC suggest it is the influence of combination by temperature, precipitation, evaporation, and original soil properties together and that the predominant factors and the interaction among these factors will vary in different geographical regions. The limitations and uncertainties of the simulation are also discussed. [Copyright &y& Elsevier]

Ammonia (NH 3) volatilization in rice paddies may be affected by elevated atmospheric CO 2 concentration ([CO 2 ]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO 2 enrichment and warming on NH 3 volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO 2 enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO 2 ] had no significant effects on NH 3 volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO 2 enrichment might offset the possible enhancement on NH 3 volatilization, as more soil N was absorbed by plant thus reducing NH 3 loss potential. Elevated temperature increased NH 3 volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH 4 +-N) concentration, pH, and urease activity. Combination of CO 2 enrichment and warming caused the highest cumulative NH 3 loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH 4 +-N concentration, pH and urease activity were also observed with co-elevation of [CO 2 ] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO 2 enrichment cause more NH 3 volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH 3 losses under future climate change. Unlabelled Image • NH 3 volatilization was monitored after 4 years of field warming and CO 2 enrichment in a rice paddy. • Elevated [CO 2 ] showed insignificant effects on NH 3 volatilization as more N was absorbed by plant. • Elevated temperature increased NH 3 volatilization by increasing soil NH 4 +-N, urease activity and pH. • More NH 3 from rice paddies might be emitted under future climate change. [ABSTRACT FROM AUTHOR]

Effectiveness of N might be modified in rice cultivation under future climate change with elevated atmospheric CO 2 concentration ([CO 2 ]). At present, limited information is available to understand how plant N uptake and N use efficiency respond to elevated [CO 2 ] and/or temperature in Chinese double rice cropping systems. A four-year field experiment was therefore conducted using open-top chambers with varying [CO 2 ] (ambient, ambient +60 μmol mol−1) and varying temperature (ambient, ambient +2 °C) in Hubei Province, Central China. Compared with ambient conditions, elevated [CO 2 ] increased plant N uptake and N use efficiency, as measured by fertilizer N recovery efficiency (NRE), N agronomic efficiency (NAE), N physiological efficiency (NPE) and apparent system N use efficiency (NUE sys), in both early rice and late rice. CO 2 enrichment tended to decrease soil mineral N concentration since more N was assimilated by plants. Elevated temperature led to lower plant N uptake and decreased NRE and NAE in early rice, due to a reduction in grain yield induced by heat injury. In contrast, warming increased plant N uptake and N use efficiency in late rice as no heat stress existed. Warming tended to increase soil mineral N concentration in early rice but had negligible effects in late rice. When elevated [CO 2 ] and temperature were combined, the positive effects of CO 2 enrichment for N utilization were able to compensate for the negative effects of warming in early rice, while the interaction was synergetic in late rice. Hence, co-elevation of [CO 2 ] and temperature led to higher N use efficiency (64.6% for NUE sys across four years) and decreased annual N surplus by 28.6–36.5 kg N ha−1 compared with ambient conditions. Our findings confirm that CO 2 enrichment and air warming can improve N use efficiency at both crop level and system level in Chinese double rice cultivation. Unlabelled Image • Warming decreases N use efficiency in early rice while increasing it in late rice. • An offset is observed for N utilization between CO 2 enrichment and warming in early rice while a synergy exists in late rice. • Effects of CO 2 enrichment and warming on soil mineral N are regulated by plant N uptake. • Co-elevation of [CO 2 ] and temperature results in higher N use efficiency and lower N surplus in double rice cultivation. [ABSTRACT FROM AUTHOR]

• Elevated [CO 2 ] and temperature jointly stimulated leaf A net before heading. • Air warming accelerated photosynthetic down-regulation under CO 2 enrichment after heading. • G s acclimated to warming and CO 2 enrichment in parallel with A net under no stress conditions. • Earlier leaf senescence, larger sink capacity or lower rice sterility might cause photosynthetic acclimation. • Co-elevation of [CO 2 ] and temperature increased dry matter productivity in Chinese double rice cultivation. Changes in atmospheric CO 2 concentration ([CO 2 ]) and temperature have impacts on leaf photosynthesis (A net) and stomatal conductance (G s) of rice, which strongly affect dry matter productivity. Understanding of the acclimation responses of A net and G s under elevated [CO 2 ] and/or temperature is limited. A field experiment of double rice (early rice-late rice rotation) was conducted using open-top chambers from 2013 to 2016 in Hubei Province, Central China, with two levels of [CO 2 ] (ambient, ambient + 60 μmol mol−1) and two levels of temperature (ambient, ambient + 2°C). Averaging across the four-year experiment, elevated [CO 2 ] and elevated temperature increased A net by 2.4 %–9.4 % and 2.4 %–10.7 %, respectively at pre-heading stages. A positive interaction was observed between elevated [CO 2 ] and temperature in early rice which further increased A net , while the interaction was not additive in late rice. Elevated [CO 2 ] caused lower G s and partly offset the stimulation of elevated temperature on G s at tillering and jointing. At post-heading stages, photosynthetic acclimation to elevated [CO 2 ] was observed as the stimulation of A net was not continued. Elevated temperature decreased A net by 1.7 %–16.6 % and further accelerated photosynthetic down-regulation by elevated [CO 2 ]. Warming reduced G s at milking and maturity in early rice because of high ambient temperature, which resulted in stomatal limitation to photosynthesis, but its effects on G s in late rice were positive because the ambient temperature was low. Generally, G s acclimated to warming and CO 2 enrichment in parallel with A net when there were no environmental constraints. Earlier leaf senescence, decreased leaf SPAD, lower seed-setting rate or larger sink capacity caused by elevated [CO 2 ] and/or temperature might directly or indirectly explain the down-regulation on photosynthesis after heading. Our results show that warming alters the acclimation of leaf photosynthesis and stomatal conductance to CO 2 enrichment and the combined effects differ between growth stages, and indicate that co-elevation of [CO 2 ] and temperature may increase dry matter productivity in the Chinese double rice cropping system. [ABSTRACT FROM AUTHOR]

• Responses to warming differed between early rice and late rice. • Warming benefited yield formation before heading. • Benefits of CO 2 enrichment could eliminate the negative effects of warming on yield. • Yield may not decrease under future climate change in Chinese double rice system. Elevated atmospheric CO 2 concentration ([CO 2 ]) and temperature can strongly affect rice (Oryza sativa L.) production. However, the impact of warming is variable depending on ambient temperature and cropping system. Little is known about the effect of elevated temperature and its interaction with elevated [CO 2 ] in the Chinese double rice cropping system. To study this issue, field experiments were conducted using open-top chambers (OTC) with varying [CO 2 ] (ambient, ambient+60 μmol mol−1) and varying temperature (ambient, ambient+2 °C) for 4 rotations of double rice from 2013 to 2016. Elevated [CO 2 ] significantly increased grain yield in both early rice and late rice. This could be attributed to greater aboveground biomass, higher panicle number (m-2), spikelet number (per panicle) and 1000-grain weight. Elevated temperature decreased yield in early rice (except for 2016) due to decreases in % filled grains and 1000-grain weight. Elevated temperature increased yield in late rice due to increases in aboveground biomass, number of panicles and spikelets, although % filled grains decreased. We found that warming had positive effects on tiller development and dry matter accumulation during the pre-heading period both in early and late rice, which contributed to yield formation. When elevated temperature and [CO 2 ] were combined, yield changed by −1.9–23.7% in early rice compared with ambient condition as warming partly offset the benefits of CO 2 enrichment, while yield increased by 14.3–18.8% in late rice due to a synergy between warming and CO 2 enrichment. The benefits of CO 2 enrichment for fertile spikelets (m-2) and aboveground biomass could reduce or eliminate the negative impacts of warming. However, there were no significant interactions between elevated temperature and [CO 2 ] in most rice seasons. Our findings indicate that warming by 2 °C is not detrimental to yield formation under CO 2 enrichment, and suggest that grain yield may not decrease under future climate change in the Chinese double rice cropping system. [ABSTRACT FROM AUTHOR]