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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]

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]

• 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]