Salt tolerance evolution facilitates antibiotic resistome in soil microbiota: Evidences from dissemination evaluation, hosts identification and co-occurrence exploration.

Salinity is considered as one of the vital factors affecting the profiles of antibiotic resistance genes (ARGs) in soils, whereby its roles in shaping the antibiotic resistome were still poorly understood. Here, metagenomic analysis was conducted to track the ARGs distributions and dissemination in soils during salt accumulation and desalinization processes. Neutral-salt accumulation for 45 and 90 days significantly increased the relative abundances of ARGs and mobile genetic elements (MGEs) carrying antibiotic resistance contigs (ARCs). The ARGs within antibiotic efflux and target protection families primarily carried by Streptomyces, Nocardioides, Rhodanobacter and Monashia were largely enriched by salinity. The ARGs subtypes of the resistance-nodulation-division (RND) family, ATP-binding cassette (ABC) family, rRNA methyltransferase and other efflux were closely associated with MGEs, contributing to the enrichment of ARGs. Moreover, the ARGs subtypes and transposons were genetically linked with the salt-tolerance mechanisms of organic osmolyte transporters and K+ uptake proteins on the same ARC, demonstrating the coselection of ARGs and halotolerant genes. Furthermore, the antibiotic resistome could recover to a normal state after the prolonged incubation by alleviating salt stress. Nevertheless, the acquisition of ARGs by opportunistic pathogens after salt treatment was increased, serving to prioritize further efforts on the health risks correlated with resistance propagation and human exposure in saline soils.

Migration and Removal of Labile Cadmium Contaminants in Paddy Soils by Electrokinetic Remediation without Changing Soil pH.

Electrokinetic remediation (EKR) is a viable, advanced cleaning strategy that can permanently reduce the toxicity of soil contaminants. However, EKR is prone to causing changes in soil pH. The negative impacts must be minimized if field-scale application is to be realized. In this study, EKR with polarity reversal was used to avoid soil pH polarization and to clean up cadmium (Cd)-contaminated paddy soils. Results showed that Cd desorbed from oxidizable and residual fractions to labile and easily available parts. Soil moisture content above 0.35 g g-1 was conductive to achieving the desirable Cd-migration rate. The exchangeable Cd phase eventually migrated from both ends of that soil compartment towards the intermediate. Moreover, the addition of citric acid at the concentration of 0.1 mol L-1 was an effective enhancement strategy. The methodology enriched Cd contaminants to specific sites. The technology can be used for electrokinetic-assisted phytoremediation during the rice growing period. Hyperaccumulator is planted in the intermediate area to remove the Cd contaminants. On the other hand, Cd removal is achieved in the region close to the electrodes. The present study provides a theoretical basis for in situ remediation. It has a wider significance for field-scale application.

Ammonium (NH4+) transport processes in the riverbank under varying hydrologic conditions.

Attenuation of groundwater ammonium (NH4+) is expected to occur through redox reaction and adsorption of the riverbank. Previous studies determined that NH4+ mostly degraded through nitrification along subsurface flow, however, the adsorption capacities of riverbanks were always ignored in the NH4+ reduction processes. In this study, field experiments were conducted in the Fuliji section of the Xiaosuixin River, China, to understand NH4+ transport and attenuation under rainfall events-induced river and groundwater interactions. The results indicated that the NH4+ concentration in river water increased significantly after heavy rainfall events and reached a peak of about 5.88 mg L-1, and the lag time was more than 2 weeks compared with the river peak stage. Adsorption plays a dominant role in attenuation of NH4+ in riverbank with high amounts of organic materials and clay minerals, reducing its concentration to less than 0.05 mg L-1. A two-dimensional lateral exchange and transport model of NH4+ was developed and calibrated against observations in the aquifer, and an exponential reduction pattern of NH4+ was identified. The model's possible implications about the effects of varying hydrologic changes (i.e., peak stage and lag time differences between river and groundwater) on NH4+ transport were also discussed. Thus, the effects of river-groundwater interactions on nitrogen pollution should be taken into consideration in river regulation strategies in order to ensure proper hydrogeochemical functioning of river-aquifer interfaces and related ecosystems.

Can ensemble machine learning be used to predict the groundwater level dynamics of farmland under future climate: a 10-year study on Huaibei Plain.

Accurate and simple prediction of farmland groundwater level (GWL) is an important aspect of agricultural water management. A farmland GWL prediction model, GWPRE, was developed that integrates four machine learning (ML) models (support vector machine regression, random forest, multiple perceptions, and the stacking ensemble model) with weather forecasts. Based on the GWL and meteorological data of five monitoring wells (N1, N2, N3, N4, and N5) in Huaibei plain from 2010 to 2020, the feasibility of predicting GWL by meteorological factors and ML algorithm was tested. In addition, the stacking ensemble model and future meteorological data after Bayesian model averaging were introduced for the first time to predict GWL under future climate conditions. The results showed that GWL showed an increasing trend in the past decade, but it will decrease in the future. The performance of the stacking ensemble model was better than that of any single ML model, with RMSE reduced by 4.26 ~ 96.97% and the running time reduced by 49.25 ~ 99.40%. GWL was most sensitive to rainfall, and the sensitivity index ranged from 0.2547 to 0.4039. The fluctuation range of GWL of N1, N2, and N3 was 1.5 ~ 2.5 m in the next decade. Due to the possible high rainfall, the GWL decreased in 2024 under RCP 2.6 and 2026 under RCP 8.5. It is worth noting that although the stacking ensemble model can improve the accuracy, it is not always the best among ML models in terms of portability. Nevertheless, the stacking ensemble model was recommended for GWL prediction under climate change.

Global benefits of non-continuous flooding to reduce greenhouse gases and irrigation water use without rice yield penalty.

Non-continuous flooding is an effective practice for reducing greenhouse gas (GHG) emissions and irrigation water use (IRR) in rice fields. However, advancing global implementation is hampered by the lack of comprehensive understanding of GHGs and IRR reduction benefits without compromising rice yield. Here, we present the largest observational data set for such effects as of yet. By using Random Forest regression models based on 636 field trials at 105 globally georeferenced sites, we identified the key drivers of effects of non-continuous flooding practices and mapped maximum GHGs or IRR reduction benefits under optimal non-continuous flooding strategies. The results show that variation in effects of non-continuous flooding practices are primarily explained by the UnFlooded days Ratio (UFR, that is the ratio of the number of days without standing water in the field to total days of the growing period). Non-continuous flooding practices could be feasible to be adopted in 76% of global rice harvested areas. This would reduce the global warming potential (GWP) of CH4 and N2 O combined from rice production by 47% or the total GWP by 7% and alleviate IRR by 25%, while maintaining yield levels. The identified UFR targets far exceed currently observed levels particularly in South and Southeast Asia, suggesting large opportunities for climate mitigation and water use conservation, associated with the rigorous implementation of non-continuous flooding practices in global rice cultivation.

Controlled Irrigation and Drainage Reduce Rainfall Runoff and Nitrogen Loss in Paddy Fields.

In southern China, the growing period of rice is synchronized with the rainy period, and the loss of nutrients (such as nitrogen) due to unreasonable irrigation and drainage, along with rainfall and runoff, has become the main source of agricultural nonpoint source pollution. The laws of runoff and nitrogen loss in paddy fields under different irrigation and drainage modes are not clear. In this study, field experiments were adopted to observe the runoff and nitrogen loss under typical rainfall and throughout the whole growth period. The results showed that, compared with the traditional irrigation and drainage mode, the controlled irrigation and drainage mode reduced the drainage of two typical rainfall processes by 47.5% and 31.3% and the peak drainage by 38.9% and 14.4%. Compared with those under the traditional irrigation and drainage mode, the average concentrations of total nitrogen, nitrate nitrogen, and ammonium nitrogen under the controlled irrigation and drainage mode were reduced by 22.2%, 22.7%, and 27.8%, respectively, during the whole rainfall process on July 21 and were decreased by 27.1%, 11.4%, and 25.6%, respectively, on August 25. In irrigated rice areas, under the controlled irrigation and drainage mode, drainage was reduced after two intercepts through paddy fields and drainage ditches. The nitrogen concentration in the drainage ditch decreased due to the increase in retention time and the effect of the ditch and field wetland. Compared with the traditional irrigation and drainage mode, the total nitrogen, nitrate nitrogen, and ammonium nitrogen loads of the controlled irrigation and drainage mode were reduced by 69.8%, 65.3%, and 69.7%, respectively.

Temperature Influenced the Comammox Community Composition in Drinking Water and Wastewater Treatment Plants.

Nitrification is a pivotal step applied in water engineered systems for nitrogen removal. Temperature variation due to seasonal changes is a great challenge for maintaining nitrogen removal efficiency in water engineered ecosystems by affecting nitrifier activities. Research on the abundance, activity, and metabolic characteristics of nitrifiers can provide information for selecting suitable design parameters to ensure efficient nitrogen removal in different seasons. To date, the temperature-related niche separation of comammox, a newly discovered nitrifier with potential high-growth yield, has been rarely investigated. This study addressed the distribution of comammox and canonical nitrifying guilds in drinking water treatment plants (DWTPs) and wastewater treatment plants (WWTPs) in different seasons. qPCR-based surveys showed that comammox ubiquitously distributed and greatly outnumbered other ammonia-oxidizing prokaryotes in both DWTPs and WWTPs, except in Aug samples from DWTPs, suggesting the potential competitive advantage of AOA in summer. The nitrificans-like comammox and nitrosa-like comammox comprised the majority of the comammox community in DWTPs and WWTPs, respectively, and COD and NH4+ concentrations significantly contributed to the distinct comammox phylotype distribution between DWTPs and WWTPs. The temperature-related distribution pattern of the comammox community was observed at each site. Moreover, the network complex of comammox communities was highest in Dec at all the sites, possibly contributing to the survival of comammox community in low temperature conditions.

A process-based coupled model of stomatal conductance-photosynthesis-transpiration during leaf ontogeny for water-saving irrigated rice.

Process-based coupled model of stomatal conductance-photosynthesis-transpiration was developed to estimate simultaneously stomatal conductance gsw, photosynthetic rate Pn, and transpiration rate Tr during leaf ontogeny. The modified Jarvis model was constructed by superposing the influence of leaf age LA on gsw in traditional Jarvis model. And the modified Farquhar model was constructed by incorporating the relationships of the LA with parameters in Farquhar model into traditional Farquhar model. The average and leaf-age-based coupled models were constructed, respectively, by combining traditional Farquhar and Penman-Monteith models with traditional Jarvis, and combining modified Farquhar and Penman-Monteith models with modified Jarvis. The results showed that the gsw, the maximum rate of carboxylation, maximum rate of electron transport, rate of triose phosphates utilization, and mitochondrial respiration rate varied in a positive skew pattern, while the mesophyll diffusion conductance decreased linearly with increase in LA. The average coupled model underestimated gsw, Pn, and Tr for young leaves and overestimated gsw, Pn, and Tr for old leaves. And the leaf-age-based coupled model generally perfected well in estimating gsw, Pn, and Tr for all leaves during leaf ontogeny. The study will provide basic information for either modeling leaf gsw, Pn, and Tr continuously, or upscaling them from leaf to canopy scale by considering the variation of LA within canopy.

Effect of biochar addition on CO2 exchange in paddy fields under water-saving irrigation in Southeast China.

Biochar has been widely applied to paddy fields to improve soil fertility, crop productivity and carbon sequestration, thereby leading to variations in the CO2 exchange between the paddy fields under flooding irrigation and the atmosphere, as indicated by many previous reports. However, few relevant reports have focused on paddy fields under water-saving irrigation. This study conducted a field experiment to investigate the effects of three biochar addition rates (0, 20 and 40 t ha-1) on the CO2 exchange between paddy fields under controlled irrigation (CI, a water-saving irrigation technique) and the atmosphere in the Taihu Lake region of Southeast China. Our results showed that biochar addition increased the paddy field ecosystem respiration (Reco) and the soil respiration rate (Rs) in the CI paddy fields. And biochar application increased the total CO2 emissions and the total soil CO2 emissions, especially at a rate of 40 t ha-1. In contrast, gross primary productivity (GPP) was decreased and the net ecosystem exchange of CO2 (NEE) was increased with biochar addition. However, biochar addition at a rate of 20 t ha-1 significantly increased the total CO2 absorption and the net CO2 absorption of the CI paddy fields (p < 0.05), whereas biochar addition at a rate of 40 t ha-1 had no effect on the total CO2 absorption and decreased the total net CO2 absorption. At the same time, biochar addition significantly increased soil catalase, invertase and urease activities and contributed substantially to the increase in soil invertase activity. In addition, the soil bacterial, fungal and actinomycetal abundances were evidently increased with biochar addition, of which the soil fungal abundance showed the greatest increase. A high correlation was observed between soil catalase and invertase activities and soil microbial abundance. Reco was highly correlated with air and soil temperatures and soil enzyme activity. A significant quadratic polynomial correlation was observed between GPP and leaf area index (p < 0.01). The combination of biochar addition at a rate of 20 t ha-1 and water-saving irrigation has the potential to increase the size of the carbon sink and promote soil enzyme and microbial activities in paddy field ecosystems.

Enhanced N2O Production Induced by Soil Salinity at a Specific Range.

Nitrous oxide (N2O) as a by-product of soil nitrogen (N) cylces, its production may be affected by soil salinity which have been proved to have significant negative effect on soil N transformation processes. The response of N2O production across a range of different soil salinities is poorly documented; accordingly, we conducted a laboratory incubation experiment using an array of soils bearing six different salinity levels ranging from 0.25 to 6.17 dS m-1. With ammonium-rich organic fertilizer as their N source, the soils were incubated at three soil moisture ( θ ) levels-50%, 75% and 100% of field capacity ( θ fc )-for six weeks. Both N2O fluxes and concentrations of ammonium, nitrite and nitrate (NH4+-N, NO2--N and NO3--N) were measured throughout the incubation period. The rates of NH4+-N consumption and NO3--N accumulation increased with increasing soil moisture and decreased with increasing soil salinity, while the accumulation of NO2--N increased first then decreased with increasing soil salinity. N2O emissions were significantly promoted by greater soil moisture. As soil salinity increased from 0.25 to 6.17 dS m-1, N2O emissions from soil first increased then decreased at all three soil moisture levels, with N2O emissions peaking at electric conductivity (EC) values of 1.01 and 2.02 dS m-1. N2O emissions form saline soil were found significantly positively correlated to soil NO2--N accumulation. The present results suggest that greater soil salinity inhibits both steps of nitrification, but that its inhibition of nitrite oxidation is stronger than that on ammonia oxidation, which leads to higher NO2--N accumulation and enhanced N2O emissions in soil with a specific salinity range.

Vertical profile of photosynthetic light response within rice canopy.

Measured leaf photosynthetic light response (PLR) curves at different positions were fitted by non-rectangular hyperbola (NRH) equation to characterize vertical profile of parameters in NRH equation, namely maximum net photosynthetic rate Pnmax, initial quantum yield of assimilation φ, dark respiration rate Rd, and convexity of the curve k, at both jointing and heading stages within rice canopy. And leaf-position-specific and canopy average NRH equations were constructed respectively based on measured PLR curves at each specific leaf position and all measured PLR curves within rice canopy. The results showed that the Pnmax, φ, and Rd reached the maximum at the top second leaf and then decreased at jointing stage and decreased in downward leaves at heading stage. The k increased with lowering leaf position at both stages. The leaf-position-specific NRH equation performed well in estimating net photosynthetic rate Pn for all leaves at different positions and stages, while the canopy average NRH equation underestimated leaf Pn at upper canopy and overestimated Pn at lower canopy. The top fourth leaf was suitable for estimating photosynthetic parameters at canopy scale, as the Pnmax, φ, Rd, and k of the top fourth leaf were near to these parameters of rice canopy, and the canopy average NRH equation performed well in estimating leaf Pn for the top fourth leaf. The results will provide basic information for upscaling leaf photosynthesis to canopy scale.

Effects of Biochar Application on Soil Organic Carbon Composition and Enzyme Activity in Paddy Soil under Water-Saving Irrigation.

Rice water-saving irrigation technology can remarkably reduce irrigation water input and maintain high yield; however, this technology can also accelerate the decomposition of soil organic matter in paddy fields. The spatial and temporal distributions of soil organic carbon (SOC), water-soluble organic carbon (WSOC), and soil microbial biomass carbon (SMBC) under different water-carbon regulation scenarios were analyzed on the basis of field experiments in the Taihu Lake region in China to explore the effects of biochar application on SOC and its components in water-saving irrigation paddy fields. The response of soil catalase (CAT) and invertase (INV) to biochar application in water-saving irrigated rice fields was clarified. The results showed that water-saving irrigation reduced the SOC content by 5.7% to 13.3% but increased WSOC and SMBC contents by 13.8% to 26.1% and 0.9% to 11.1%, respectively, as compared with flooding irrigation. Nonflooding management promoted the oxidative decomposition of soil organic matter. Two years after straw biochar was added, paddy soil SOC content under water-saving irrigation was increased by 4.0% to 26.7%. The WSOC and SMBC contents were also increased by 4.0% to 52.4% and 7.0% to 40.8%, respectively. The high straw biochar addition rate exhibited great impact on SOC. Remarkable correlations among SOC, WSOC, and SMBC were observed, indicating that the addition of straw biochar improved soil labile C, such as WSOC and SMBC, which promoted SOC transformation and stability in paddy soil under water-saving irrigation. Soil CAT and INV were related to SOC conversion. In conclusion, the combination of water-saving irrigation and straw biochar addition was beneficial to the improvement of soil properties and fertility of paddy fields.

A general non-rectangular hyperbola equation for photosynthetic light response curve of rice at various leaf ages.

Photosynthetic light response (PLR) curves of leaves are usually fitted by non-rectangular hyperbola (NRH) equation, and those fitted NRH parameters may change with leaf aging. The objectives of this study were 1) to reveal the response of NRH parameters of rice leaves, light-saturated net photosynthetic rate (Pnmax), quantum yield of assimilation (φ), dark respiration rate (Rd) and convexity of the curve (k), to leaf age; and 2) to improve the performance of NRH equation in simulating the PLR curves for leaves at various ages. The PLR for rice leaves at ages of 3-53 days were measured, and the general NRH equation was developed by incorporating the relationship between NRH parameters and leaf age into the NRH equation. The results showed that the NRH parameters of Pnmax, φ and Rd increased rapidly to maximum at approximately 10 days and then declined linearly toward the age of 53 days. However, the value of k was not sensitive to leaf age. The general NRH equation can be used to simulate leaf PLR continuously along with leaf aging.

Effects of biochar addition on the NEE and soil organic carbon content of paddy fields under water-saving irrigation.

The addition of biochar has been reported as a strategy for improving soil fertility, crop productivity, and carbon sequestration. However, information regarding the effects of biochar on the carbon cycle in paddy fields under water-saving irrigation remains limited. Thus, a field experiment was conducted to investigate the effects of biochar addition on the net ecosystem exchange (NEE) of CO2 and soil organic carbon (SOC) content of paddy fields under water-saving irrigation in the Taihu Lake region of China. Four treatments were applied: controlled irrigation (CI) without biochar addition as the control (CA), CI with biochar addition at a rate of 20 t·ha-1 (CB), CI with biochar addition at a rate of 40 t·ha-1 (CC), and flooding irrigation (FI) with biochar addition at a rate of 40 t·ha-1 (FC). Biochar addition increased rice yield and irrigation water use efficiency (IWUE) by 24.0-36.3 and 33.4-42.5%, respectively, compared with the control. In addition, biochar addition increased the NEE of CI paddy fields. The average NEE of paddy fields under CB and CC was 2.41 and 30.6% higher than that under CA, respectively. Thus, the increasing effect of biochar addition at a rate of 40 t·ha-1 was considerably better than those of the other treatments. Apart from biochar addition, irrigation mode was also identified as an influencing factor. CI management increased the NEE of paddy fields by 17.6% compared with FI management. Compared with CA, CB increased total net CO2 absorption by 10.0%, whereas CC decreased total net CO2 absorption by 13.8%. Biochar addition also increased SOC, dissolved organic carbon, and microbial biomass carbon contents. Therefore, the joint regulation of biochar addition and water-saving irrigation is a good technique for maintaining rice yield, increasing IWUE, and promoting soil fertility. Furthermore, when amended at the rate of 20 t·ha-1, biochar addition will be a good strategy for sequestering carbon in paddy fields.

Reducing Surface Wetting Proportion of Soils Irrigated by Subsurface Drip Irrigation Can Mitigate Soil N2O Emission.

To reveal the impact of soil moisture distributions on nitrous oxide (N2O) emissions from wet soils irrigated by sub-surface drip irrigation (SDI) with different surface soil wetting proportions, pot experiments were conducted, with surface irrigation (SI) as a control. Results indicated that irrigation triggered N2O pulsing effect in all SDI treatments, yet N2O values reduced with the decrease of surface soil wetting proportions of SDI irrigated soils, and the occurrence times were lagged. The peak N2O fluxes and the corresponding soil water filled pore space (WFPS), as well as the coefficients of determination (R²) of the exponential function between N2O fluxes and soil WFPS, decreased with the reduction of surface soil wetting proportions with SDI treatment, and from the central sub-region to the periphery sub-region. The pulse period contributed most to the reduction of N2O emissions in SDI compared to SI treatments and should be a key period for N2O emission mitigation. Over the whole experimental period, the area-weighted average cumulative N2O fluxes from SDI treatments were 82.3⁻157.3 mg N2O m-2 lower than those from SI treatment, with periphery sub-regions of R3 and R4 (radius of 19⁻27 cm and 28⁻36 cm from the emitter horizontally) contributing to more than 75.8% of the total N2O emission mitigation. These results suggest that reducing surface soil wetting proportions or the increments of topsoil WFPS for SDI irrigated soils is a promising strategy for N2O emission reduction.

Effects of Biochar Amendment on CO2 Emissions from Paddy Fields under Water-Saving Irrigation.

The role of carbon pool of biochar as a method of long-term C sequestration in global warming mitigation is unclear. A two-year field study was conducted to investigate the seasonal variations of CO2 emissions from water-saving irrigation paddy fields in response to biochar amendment and irrigation patterns. Three biochar treatments under water-saving irrigation and one biochar treatment under flooding irrigation were studied, and the application rates were 0, 20, 40, and 40 t ha-1 and labeled as CI + NB (controlled irrigation and none biochar added), CI + MB (controlled irrigation and medium biochar added), CI + HB (controlled irrigation and high biochar added), and FI + HB (flood irrigation and high biochar added), respectively. Results showed that biochar application at medium rates (20 t ha-1) decreased CO2 emissions by 1.64⁻8.83% in rice paddy fields under water-saving irrigation, compared with the non-amendment treatment. However, the CO2 emissions from paddy fields increased by 4.39⁻5.43% in the CI + HB treatment, compared with CI + NB. Furthermore, the mean CO2 emissions from paddy fields under water-saving irrigation decreased by 2.22% compared with flood irrigation under the same amount of biochar application (40 t ha-1). Biochar amendment increased rice yield and water use efficiency by 9.35⁻36.30% and 15.1⁻42.5%, respectively, when combined with water-saving irrigation. The CO2 emissions were reduced in the CI + MB treatment, which then increased rice yield. The CO2 emissions from paddy fields were positively correlated with temperature. The highest value of the temperature sensitivity coefficient (Q10) was derived for the CI + MB treatment. The Q10 was higher under water-saving irrigation compared with flooding irrigation.

Effect of straw return on soil respiration and NEE of paddy fields under water-saving irrigation.

Straw return (SR) and rice water-saving irrigation (WSI) affect the greenhouse gas emission of paddy fields. However, studies on CO2 exchange between paddy fields and the atmosphere with joint regulation of SR and WSI are few. We conducted a two-year field experiment to investigate the effects of SR on soil respiration and net ecosystem exchange of CO2 (NEE) in paddy fields under controlled irrigation (CI), which is a typical WSI technique. The rice yields, irrigation water use efficiency, seasonal variations in soil respiration, NEE, and soil organic carbon content were measured. Compared with the control (flooding irrigation and traditional chemical fertilizer), a significant increase in rice yield and irrigation water use efficiency in the paddy fields under CI and SR joint management (CS) was observed. CS increased the soil respiration rate during most of the rice growth stage and increased the net CO2 absorption rate before approximately 80 days after transplanting; afterward, the pattern reversed. Total CO2 emissions through soil respiration in CS paddy fields increased by 43.7% and 182% compared with the control in 2014 and 2015, respectively. However, CS also caused an increase in the total net CO2 absorption by 18.1% and 30.1% in these two years, respectively. The acceleration in the consumption and decomposition of soil organic carbon induced by frequent alternate wet-dry cycles of the CI paddy fields increased the soil respiration and decreased the net CO2 absorption. SR promoted soil respiration but also improved rice growth, increasing the net CO2 absorption. The soil organic carbon content of the CS paddy fields after harvesting increased by 23.2% compared with that before transplanting. The present study concluded that joint regulation of WSI and SR is an effective measure for maintaining yield, increasing irrigation water use efficiency, mitigating CO2 emission, and promoting paddy soil fertility.

Water Salinity Should Be Reduced for Irrigation to Minimize Its Risk of Increased Soil N2O Emissions.

To reveal the effect of irrigation salinity on soil nitrous oxide (N2O) emission, pot experiments were designed with three irrigation salinity levels (NaCl and CaCl2 of 1, 2.5 and 4 g/L equivalence, Ec = 3.6, 8.1 and 12.7 ds/m), either for 0 kg N/ha (N0) or 120 kg N/ha (N120) nitrogen inputs. N2O emissions from soils irrigated at different salinity levels varied in a similar pattern which was triggered by soil moisture dynamics. Yet, the magnitudes of pulse N2O fluxes were significantly varied, with the peak flux at 5 g/L irrigation salinity level being much higher than at 2 and 8 g/L. Compared to fresh water irrigated soils, cumulative N2O fluxes were reduced by 22.7% and 39.6% (N0), 29.1% and 39.2% (N120) for soils irrigated with 2 and 8 g/L saline water, while they were increased by 87.7% (N0) and 58.3% (N120) for soils irrigated with 5 g/L saline water. These results suggested that the effect degree of salinity on consumption and production of N2O might vary among irrigation salinity ranges. As such, desalinating brackish water to a low salinity level (such as 2 g/L) before it is used for irrigation might be helpful for solving water resources crises and mitigating soil N2O emissions.

Soil degassing during watering: An overlooked soil N2O emission process.

Pulse diffusive nitrous oxide (N2O) emission following water application is well documented, whereas N2O emission caused by soil water-air displacement during the watering process (termed as soil degassing) has been largely overlooked. Watering-induced N2O emissions from ten different soils in China were quantified, and found to range from 74.4 ±â€¯6.7 to 678.1 ±â€¯36.6 µg N2O m-2 h-1 in surface watered (SW) soils, and from 45.6 ±â€¯4.4 to 358.1 ±â€¯23.6 µg N2O m-2 h-1 in subsurface watered (SUW) soils. These N2O fluxes were much larger than the diffusive N2O flux from the same soil either under dry (7.9%-9.6% water filled pore space, WFPS) or wet (85.1%-93.6% WFPS) conditions. The watering process (the water infiltration process upon irrigation/rainfall or the process of shallow groundwater uplifting) resulted in massive N2O emissions.