Search

Aquaculture ponds are an important artificial aquatic system for global food fish production but also are a hot spot of greenhouse gas (GHG) emissions. The GHG mitigation strategy and the underlying mechanism for aquaculture ponds are still poorly understood. In this study, we conducted a 2 year field experiment to determine the effects of planting high-stalk rice (an artificially bred emergent plant for ponds) on GHG emissions from aquaculture ponds. Our results showed that planting high-stalk rice reduced CH 4 emission by 64.4% and N 2 O emission by 76.2% over 2 years. Planting high-stalk rice significantly increased the content of O 2 and the abundance of pmo A in the sediment, thus prompting CH 4 oxidation in the ponds. The reduction of N 2 O emission from ponds was attributed to the decreased inorganic nitrogen, amoA-B and nir S in the sediment induced by rice. Furthermore, high-stalk rice culture in the pond increased shrimp yields and gained rice yields, resulting in a significant reduction of yield-scaled global warming potential. Our findings suggest that breeding appropriate emergent aquatic plants is a potential pathway to mitigate GHG emission from aquaculture ponds with more food yields and economic benefits.

Rice is a staple food for nearly half of the world's population, but rice paddies constitute a major source of anthropogenic CH 4 emissions. Root exudates from growing rice plants are an important substrate for methane-producing microorganisms. Therefore, breeding efforts optimizing rice plant photosynthate allocation to grains, i.e., increasing harvest index (HI), are widely expected to reduce CH 4 emissions with higher yield. Here we show, by combining a series of experiments, meta-analyses and an expert survey, that the potential of CH 4 mitigation from rice paddies through HI improvement is in fact small. Whereas HI improvement reduced CH 4 emissions under continuously flooded (CF) irrigation, it did not affect CH 4 emissions in systems with intermittent irrigation (II). We estimate that future plant breeding efforts aimed at HI improvement to the theoretical maximum value will reduce CH 4 emissions in CF systems by 4.4%. However, CF systems currently make up only a small fraction of the total rice growing area (i.e., 27% of the Chinese rice paddy area). Thus, to achieve substantial CH 4 mitigation from rice agriculture, alternative plant breeding strategies may be needed, along with alternative management., (© 2018 John Wiley & Sons Ltd.)

Elevated atmospheric CO2 (eCO2) generally increases carbon input in rice paddy soils and stimulates the growth of methane‐producing microorganisms. Therefore, eCO2 is widely expected to increase methane (CH4) emissions from rice agriculture, a major source of anthropogenic CH4. Agricultural practices strongly affect CH4 emissions from rice paddies as well, but whether these practices modulate effects of eCO2 is unclear. Here we show, by combining a series of experiments and meta‐analyses, that whereas eCO2 strongly increased CH4 emissions from paddies without straw incorporation, it tended to reduce CH4 emissions from paddy soils with straw incorporation. Our experiments also identified the microbial processes underlying these results: eCO2 increased methane‐consuming microorganisms more strongly in soils with straw incorporation than in soils without straw, with the opposite pattern for methane‐producing microorganisms. Accounting for the interaction between CO2 and straw management, we estimate that eCO2 increases global CH4 emissions from rice paddies by 3.7%, an order of magnitude lower than previous estimates. Our results suggest that the effect of eCO2 on CH4 emissions from rice paddies is smaller than previously thought and underline the need for judicious agricultural management to curb future CH4 emissions. [ABSTRACT FROM AUTHOR]

Both spikelet removal and low temperature stress largely reduced photosynthate allocation to wheat grain; the former stimulated the average N2O emissions by 31.3% and 33.2% under the field and pot conditions; the latter increased average N2O emission by 19.9% under pot condition. Spikelet removal and low temperature stress significantly reduced total plant N uptake, thereby increasing soil NO3–-N content, and increased root biomass. Our findings indicated that photosynthate allocation affects the soil N2O emissions from wheat fields through altering plant N uptake and root growth, and suggest that promoting photosynthate allocation to grain may not only benefit higher wheat yield but also mitigate greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Global warming often affects crop yield and greenhouse gas emissions from cropland. However, the effects of warming on rice yield and methane (CH 4) emissions from rice paddies in the tropical double-rice cropping systems are still unknown. Therefore, we conducted a field experiment to investigate the effect of warming on rice growth and CH 4 emissions in a Chinese tropical double-rice cropping system, using the free air temperature increase facility. The results showed that warming did not affect the rice plant biomass, but significantly reduced the early rice yield by 5.0% and late rice yield by 6.5%. Warming trended to increase CH 4 emissions, especially in the flooded stage of early rice seasons. Warming significantly stimulated the abundance of methanogens and methanotrophs, and CH 4 production and oxidation potential by 93.3%, 84.3%, 29.3% and 66%, respectively. Warming non-significantly increased the soil dissolved organic carbon concentrations, but significantly reduced the soil NH 4 + concentrations. Warming significantly increased yield-scaled CH 4 emissions by 7–41%. Our findings suggest that warming may reduce rice yield but increase CH 4 emissions from the Chinese tropical double-rice cropping systems and underline the need for agricultural practices of higher rice yield and lower CH 4 emissions. • The study was conducted in a Chinese tropical double-rice system. • Warming trended to increase CH 4 emissions, especially in the flooded stage. • Warming increased the abundances of methanogens and methanotrophs. • Warming significantly reduced rice yield and increased yield-scaled CH 4 emissions. [ABSTRACT FROM AUTHOR]

Atmospheric CO 2 concentrations and water management practices both affect greenhouse gas (GHG) emissions from rice paddies, but interactive effects between these two factors are still unknown. Here, we show the first study to compare the impact of elevated atmospheric CO 2 (eCO 2) on GHG emissions under continuously flooded irrigation (CF) and under intermittently flooded (IF) conditions. Elevated CO 2 stimulated CH 4 emissions under CF by 50% in a field experiment and by 46% in a pot experiment, but it had no effect under IF in both experiments. Elevated CO 2 had no effect on N 2 O emissions in either the field or pot experiment. Rice root biomass, aboveground biomass and grain yield increased with eCO 2 , but were not affected by water management. Elevated CO 2 only stimulated the abundance of methanogens under CF, suggesting that increased soil O 2 availability with IF limited methanogenic activity under eCO 2. Our findings suggest that estimates of CH 4 emissions from global rice agriculture with eCO 2 need to account for recent changes in water management. • The first study to compare the effect of elevated CO 2 on GHG emissions under CF and IF. • Elevated CO 2 stimulated CH 4 emissions under CF, but had no effect under IF. • Elevated CO 2 did not affect N 2 O emissions under CF and IF. • Elevated CO 2 increased the abundance of methanogens under CF only. • Current estimates of CO 2 effects on CH 4 emissions from rice paddies may be too high. [ABSTRACT FROM AUTHOR]

Organic amendment often affects both crop yield and greenhouse gas (GHG) emission. Yet the impact of organic amendment on yield gains and GHG emissions is still unclear, particularly in long-term soybean-wheat cropping system. Based on a 30-year soybean-wheat cropping system experiment, the impact of organic amendments (i.e. straw and manure) on soil properties, crop yield, N 2 O and CH 4 emissions, and net ecosystem economic budget (NEEB) were investigated. The treatments were: chemical NPK fertilizer (NPK), chemical NPK plus low amount of wheat straw (NPKLS), chemical NPK plus high amount of wheat straw (NPKHS), chemical NPK plus pig manure (NPKPM), chemical NPK plus cattle manure (NPKCM), and a control with no fertilizer applied (CK). The long-term straw and manure amendments enhanced soybean yield by 13.1% and 44.0%, and improved wheat yield by 6.4% and 9.9%, respectively. Meanwhile, they stimulated N 2 O emissions by 25.1% and 49.0% respectively, without significant effect on CH 4 emissions, compared to the chemical NPK fertilizer treatment (NPK). The results of structural equation model showed that soil properties tested explained 76% of the variations observed in N 2 O emissions, which were directly affected by soil nitrification capacity, pH and denitrification capacity. Although straw and manure amendments increased the total GHG emissions investigated by 25.7% and 48.6% respectively, they showed insignificant effects on the greenhouse gas intensity (GHGI), and increased NEEB by 8.6% and 21.1%, respectively, compared to the NPK treatment. This indicates that the benefits arising from crop yield improvement through the use of organic amendments can cover the carbon fees caused by increased GHG emissions. Our findings suggest that organic amendment can be an effective strategy to simultaneously increase crop yield while mitigating greenhouse gas emissions from the perspective of carbon fees. [Display omitted] • Organic amendments stimulated total GHG emissions of N 2 O and CH 4. • Soil properties tested explained 76% of the variation in N 2 O emissions. • Organic amendments improved yield without increasing the greenhouse gas intensity. • Straw and manure amendments increased the net ecosystem economic budget. [ABSTRACT FROM AUTHOR]

Rice paddies contribute to ∼48% of greenhouse gas emissions from cropland, with ∼94% from methane (CH 4). Elevated atmospheric CO 2 concentrations (eCO 2) due to human activities, generally stimulate the rice growth, and in turn affect CH 4 emissions from rice paddies. However, the effects of eCO 2 on CH 4 emissions from rice paddies are still unclear under in situ straw incorporation, the popular agricultural practice. Therefore, we conducted a 3-yr field experiment to investigate the effects of eCO 2 on CH 4 emissions under in situ straw incorporation in the rice-wheat cropping system, using the open-top chamber technology. We found that eCO 2 reduced the CH 4 emissions from rice paddies by 10.9–23.8%, but increased rice plant biomass by 4.2–35.6%. The eCO 2 reduced the soil NH 4 + and NO 3 - concentrations, but did not affect the soil dissolved organic C. The eCO 2 did not affect the abundance of methanogens and CH 4 production potential, whereas it stimulated the abundance of methanotrophs and CH 4 oxidation potential by 102.5% and 15.1%, respectively. The eCO 2 also shifted the community composition of methanotrophs and reduced the relative abundance of type Ⅱ methanotrophs by 8.5%. The random forest analysis identified that soil CH 4 oxidation potential is the most important factor affecting CH 4 emissions. Our findings indicate that eCO 2 can reduce the CH 4 emissions from rice paddies under in situ straw incorporation mainly through increasing the soil CH 4 oxidation potential. Our study suggests the effects of eCO 2 on CH 4 emissions from global paddies may be overestimated and underline the need for smart agricultural management to reduce CH 4 emissions. • Elevated CO 2 reduced CH 4 emission from paddies under in situ straw incorporation. • Elevated CO 2 stimulated abundance of methanotrophs and CH 4 oxidation potential. • Soil CH 4 oxidation potential is the most important factor affecting CH 4 emissions. [ABSTRACT FROM AUTHOR]

Rice paddies supply the staple food for 50% global population, but contribute 48% of greenhouse gas (GHG) emissions from croplands. Temperature is the key factor of rice yield and GHG emissions, but warming effects (i.e. elevated temperature ≤ 2°C) are still unclear, especially in hotspots. Therefore, we collected the global in-situ observations of warming experiments and corresponding environmental factors to identify the key drivers of warming effects, and developed the statistic models to assess the effects of warming on GHG emissions from China's rice paddies. Our results indicate that the variation in warming effects on rice yield, methane (CH 4) emissions, and nitrous oxide (N 2 O) emissions are primarily explained by ambient temperature of post-anthesis, ambient temperature of flooding stage, and soil pH, respectively. Considering these key factors, we estimate that warming does not significantly affect China's total rice yield, while can increase CH 4 emissions by 13.6% °C−1, N 2 O emissions by 30.5% °C−1, and area-/yield-scaled GHG emissions by 14.9% °C−1 from China's rice paddies. Warming reduces rice yield but increases GHG emissions more strongly in East, South and Central China, compared to North, Northwest, Northeast, and Southwest China. Our findings quantify the warming effects on rice yield and GHG emissions, and provide new perspectives for the hotpots of warming effects on China's rice production. In the warmer future, we still need more efforts on smart adaptation strategies to maintain rice yield and curb GHG emissions from rice agriculture. • Temperature and soil pH can explain variation in warming effect on GHG emissions. • Warming effect on N 2 O emissions shows a negative relationship with soil pH. • Warming does not affect China's total rice yield while increases GHG emissions. • Warming increases yield-scaled GHG emissions by 14.9% °C−1 in China's paddies. • East, South and Central China's rice paddies are the hotspots of warming effects. [ABSTRACT FROM AUTHOR]