Effects of Non-flooded Cultivation with Straw Mulching on Rice Agronomic Traits and Water Use Efficiency

A field experiment was conducted to study water use efficiency and agronomic traits in rice cultivated in flooded soil and non-flooded soils with and without straw mulching. The total amount of water used by rice under flooded cultivation （FC） was 2.42 and 3.31 times as much as that by rice under the non-flooded cultivation with and without straw mulching, respectively. The average water seepage was 13 560 m^3/ha under the flooded cultivation, 4 750 m^3/ha under the non-flooded cultivation without straw mulching （ZM） and 4 680 m^3/ha under non-flooded cultivation with straw mulching （SM）. The evapotranspiration in the SM treatment was only 38.2% and 63.6% of the FC treatment and ZM treatment, respectively. Compared with the ZM treatment, straw mulching significantly increased leaf area per plant, main root length, gross root length and root dry weight per plant of rice. The highest grain yield under the SM treatment （6 747 kg/ha） was close to the rice cultivated in flooded soil （6 811.5 kg / ha）. However, the yield under the ZM treatment （4 716 kg/ha） was much lower than that under the FS treatment and SM treatment. The order of water use efficiency and irrigation water use efficiency were both as follows： SM〉 ZM〉 FC.

Effects of Different Irrigation Amounts on Physiological Indexes and Water Use Efficiency of Rice at the Jointing-booting Stage

[Objective] This study was conducted to investigate the effects of different irrigation amounts on rice leaf physiology and water use efficiency. [Method] The irrigation test with three different treatments was carried out in the Agrometeo- rological Experimental Station of Nanjing University of Information Science ＆ Technology. [Reset] Under flood irrigation, the rice leaf temperature was lower than wet irrigation by 0.4-0.7 ℃; when the strength of photosynthetically active radiation was in the range of 800-1 800 gmol/（m^2·s）, the average stomatal conductance of rice leaves under flood irrigation was higher than that of the wet irrigation treatment by 0.123-0.183 mol H2O/（m^2·s）, and the leaf water use efficiency was higher than that of the wet irrigation treatment by 0.24 g/kg; after 10：00 every day, the water use efficiency under flood irrigation was always higher than that of the wet irrigation treatment; and compared with the wet irrigation treatment, the rice of the flood irrigation treatments had higher leaf water use efficiency, and final yields were also remarkably improved by 5.89%-13.97%. [Conclusion] This study will provide a practical reference basis for field management.

Grain yield and water use efficiency of super rice under soil water deficit and alternate wetting and drying irrigation

This study investigated if super rice could better cope with soil water deficit and if it could have better yield performance and water use efficiency （WUE） under alternate wetting and drying （AWD） irrigation than check rice. Two super rice cultivars and two elite check rice cultivars were grown in pots with three soil moisture levels, well watered （WW）, moderate water deficit （MWD） and severe water deficit （SWD）. Two cultivars, each for super rice and check rice, were grown in field with three irrigation regimes, alternate wetting and moderate drying （AWMD）, alternate wetting and severe drying （AWSD） and conventional irrigation （CI）. Compared with that under WW, grain yield was significantly decreased under MWD and SWD treatments, with less reduction for super rice than for check rice. Super rice had higher percentage of productive tillers, deeper root distribution, higher root oxidation activity, and greater aboveground biomass production at mid and late growth stages than check rice, especially under WMD and WSD. Compared with CI,AWMD increased, whereasAWSD decreased grain yield, with more increase or less decrease for super rice than for check rice. Both MWD and SWD treatments and eitherAWMD orAWSD regime significantly increased WUE compared with WW treatment or CI regime, with more increase for super rice than for check rice. The results suggest that super rice has a stronger ability to cope with soil water deficit and holds greater promising to increase both grain yield and WUE by adoption of moderate AWD irrigation.

Response of Gas Exchange and Water Use Efficiency to Light Intensity and Temperature in Transgenic Rice Expressing PEPC and PPDK Genes

Aiming to controvert whether the photosynthetic capacity of transgenic rice expressing C4 genes is enhanced, with the C3-type untransformed rice （WT） and maize （a C4 plant） as controls, the activity of C4 photosynthetic enzymes, gas exchange parameters and water use efficiency （WUE） under different light intensities and temperatures, the stable carbon isotope ratio （8-3C） value and the metabolic index of active oxygen as well as plant yield parameters were determined in transgenic rice carrying the PEPC and PPDK genes （CK） in this study. The results showed that the light-saturated photosynthetic rate of CK was intermediate between that of WT and maize, with a slight bias towards that of maize. Under a high light intensity （1 200 μmol m^-2 s^-1） and high temperature （35℃）, CK still exhibited higher photosynthetic capacity, while the Gs decreased. The WUE of CK was only slightly increased, and was similar to that of WT. The δ13C value indicated that CK functioned as a C3 plant. In addition, the tolerance to photo-oxidation and grain yield of CK was enhanced by sprayed with NaHSO3. In conclusion, CK possesses higher photosynthetic productivity under the conditions of high photon flux density （PFD）, high temperature and spraying with NaHSO3 solution, thereby providing a new technical approach and physiological basis for constructing C4-like rice.

Study on Intermittent Irrigation for Paddy Rice: I. Water Use Efficiency

A field experiment was conducted in a well-puddled paddy field developed on the Tama River alluvial soil in the Farm of Tokyo University of Agriculture and Technology, Japan, to study the effect of intermittent irrigation on water use efficiency of paddy rice. Four treatments were arranged with 2 replicates: continuous flooding irrigation treatments (CFI), and three intermittent irrigation treatments Ⅱ-0, Ⅱ-1 and Ⅱ-2, in which plants were re-irrigated when the soil water potential fell below 0, -10, and -20 kPa, respectively, at soil depth of about 5 cm. Water consumption was lower in treatment Ⅱ-0 than in treatment CFI because the percolation rate was reduced by the reduction in the hydraulic head of ponded water. Intermittent irrigation led to soil repeated shrinking and swelling in Ⅱ-1 and Ⅱ-2 plots and, therefore, soil cracks developed rapidly. Since they became the major routes of water percolation, the soil cracks increased water consumption in treatments Ⅱ-1 and Ⅱ-2. There were no significant differences in dry matter production and grain yields between treatment Ⅱ-0 and treatment CFI, but the dry matter production and grain yields in treatments Ⅱ-0 and CFI were significantly higher than those in treatments Ⅱ-1 and Ⅱ-2. Therefore, the water use efficiency in the treatments was in the order of Ⅱ-0 > CFI > Ⅱ- 2 > Ⅱ- 1.

Relation of Root Growth of Rice Seedling with Nutrition and Water Use Efficiency Under Different Water Supply Conditions

Water deficiency is one of the primary yield-limiting factors in rice. In plants, the nutrition and water use efficiency depend on root growth efficiency under different water supply conditions （WSC）. Three rice genotypes, Azucena （an upland japonica）, IR1552 （a lowland indica） and Jia 9522 （a lowland japonica）, were grown under different WSC with 0 cm （submerged）, 40 cm and 80 cm groundwater levels below the soil surface to investigate the root parameters, water use efficiency, nitrogen, phosphorous and potassium contents, net photosynthetic rate and transpiration rate of the rice plant. The relative parameters were defined as the ratio of the parameters under submerged conditions （0 cm groundwater level below soil surface） to these under upland conditions （40 cm and 80 cm groundwater levels below soil surface）. The results indicated that different genotypes showed different relative root parameters and relative nutrition content and water use efficiency under different WSC. The length and number of adventitious root are more important than seminal root length in water and nutrition uptake, and maintaining the grain yield and increasing dry matter, but the adventitious root number could not be served as an index for screening drought-resistant genotypes. Furthermore, different drought-resistant genotypes have been also found, and Azucena was resistant to drought, IR1552 sensitive to drought and Jia 9522 neither sensitive nor resistant to drought.

Effects of Continuous Plastic Film Mulching on Soil Bacterial Diversity, Organic Matter and Rice Water Use Efficiency

Two field experiments were conducted to study the effects of 6-year plastic film mulching on bacterial diversity, organic matter of paddy soil and water use efficiency on different soils with great environmental variabilities in Zhejiang Province, China, under non-flooding condition. The experiment started in 2001 at two sites with one rice crop annually. Three treatments included plastic film mulching with no flooding (PM), no plastic film mulching and no flooding (UM), and traditional flooding management (TF). Soil samples were collected and analyzed for bacterial diversity by DGGE and organic matter content, and water use efficiency (WUE) was calculated. The results showed that PM treatment favored the development of a more total bacterial community compared with TF management, the total number of bands was 33.3, 31.7 at tiller stage and heading stage (p < 0.05*). Hence, organic matter content was decreased by 36.7% and 51.4% under PM at two sites. PM also produced similar rice grain yield as TF at Duntou site and Dingqiao site, the average was 7924 kg?ha?1 and 7015 kg?ha?1 for PM and 8150 kg?ha?1 and 6990 kg?ha?1 for TF, respectively. Compared to TF, WUE and irrigation water use efficiency were increased significantly by 70.2% - 80.4% and 273.7% - 1300.0% for PM. It is essential to develop the water-saving agriculture.

Balanced Fertilization and the Effect of Fertilization on Water Use Efficiency of Upland Winter Wheat in Western Henan, China

A study on balanced fertilization was conducted by means of long-term field experiments, and a convenient table for balanced fertilization was compiled. The experimental results about the effect of fertilization on water use efficiency of upland wheat showed that the input of inorganic fertilizer should be reduced in dry years.

Genome-Wide Association Study of Nitrogen Use Efficiency and Agronomic Traits in Upland Rice

Genome-wide association study(GWAS)was performed for 16 agronomic traits including nitrogen use efficiency(NUE)and yield-related components using a panel of 190 mainly japonica rice varieties and a set of 38390 single nucleotide polymorphism(SNP)markers.This panel was evaluated under rainfed upland conditions in Madagascar in two consecutive cropping seasons with two contrasted nitrogen input levels.Using another set of five grain traits,we identified previously known genes(GW5,GS3,Awn1 and Glabrous1),thus validating the pertinence and accuracy of our datasets for GWAS.A total of 369 significant associations were detected between SNPs and agronomic traits,gathered into 46 distinct haplotype groups and 28 isolated markers.Few association signals were identified for the complex quantitative trait NUE,however,larger number of quantitative trait loci(QTLs)were detected for its component traits,with 10 and 2 association signals for nitrogen utilization efficiency and nitrogen uptake efficiency,respectively.Several detected association signals co-localized with genes involved in nitrogen transport or nitrogen remobilization within 100 kb.The present study thus confirmed the potential of GWAS to identify candidate genes and new loci associated with agronomic traits.However,because of the quantitative and complex nature of NUE-related traits,GWAS might have not captured a large number of QTLs with limited effects.

Effect of Varied Irrigation Scheduling with Levels and Times of Nitrogen Application on Yield and Water Use Efficiency of Aerobic Rice

More rice needs to be produced with lesser water to feed the increasing human population. Judicious water management practices and appropriate water saving technologies in rice cultivation are in need in the coming decades. Aerobic rice is one of water saving method of rice cultivation. The field experiment was conducted during Summer season of February 2018 to May 2018 at Tamil Nadu Agricultural University, Agricultural College and Research Institute, Madurai, to find out the effect of irrigation schedules with varied doses and time of nitrogen application on yield of aerobic rice. Irrigation scheduling of IW/CPE (Irrigation Water/Cumulative Pan Evaporation) 1.0 up to panicle initiation stage and thereafter IW/CPE 1.2 up to dough stage recorded higher yield attributes viz., number of panicles hill-1 (9.1), number of filled grains panicle-1 (87.9), test weight (15.3 g), grain yield (4462 kg·ha-1), straw yield (5977 kg·ha-1). However, the highest water use efficiency (6.8 kg·ha-1·mm-1) was recorded in the treatment of IW/CPE 1.0 throughout the crop growth period. Lower yield attributes, yield and water use efficiency were recorded with irrigation scheduling of IW/CPE 0.8 throughout the growth stage. Application of nitrogen at 150 kg·ha-1 in 5 equal splits at 20, 35, 50, 65 and 80 DAS (Days after sowing) recorded higher yield attributes viz., number of panicles hill-1 (9.3), number of filled grains panicle-1 (90.5), test weight (15.4 g), grain yield (4746 kg·ha-1), straw yield (6258 kg·ha-1) and WUE (7.5 kg·ha-1·mm-1). Application of nitrogen 100 kg·ha-1 in 4 equal splits at 20, 40, 60 and 80 DAS recorded lower yield attributes, yield and water use efficiency. The interaction effect between irrigation scheduling and nitrogen management on yield was significant. The combination of IW/CPE 1.0 up to panicle initiation stage and thereafter IW/CPE 1.2 up to dough stage along with application of nitrogen at 150 kg·ha-1 in 5 equal splits at 20, 35, 50, 65 and 80 DAS significantly produced higher number of panicles hill-1 (10.7), grain yield of 5419 kg·ha-1 and straw yield of 6906 kg·ha-1. However, IW/CPE 1.0 throughout the growth period along with application of nitrogen at 150 kg·ha-1 in 5 equal splits at 20, 35, 50, 65 and 80 DAS registered the highest water use efficiency (8.4 kg·ha-1·mm-1) in aerobic rice.

Much Improved Water Use Efficiency of Rice under Non-Flooded Mulching Cultivation

Water shortage is increasingly limiting the luxury use of water in rice cultivation. In this study, non-flooded mulching cultivation of rice only consumed a fraction of the water that was needed for traditional flooded cultivation and largely maintained the grain yield. We also investigated the growth and development of rice plants and examined grain yield formation when rice was subjected to non-flooded mulching cultivation. One indica hybrid rice combination was grown in a field experiment and three cultivation methods, traditional flooding （TF）, non-flooded straw mulching cultivation （SM） and non-flooded plastic mulching cultivation （PM）, were conducted during the whole season. Grain yield showed that there was no significant difference between SM and TF rice, but the grain yield of SM cultivation was significantly higher than that of PM. The tiller numbers were inhibited in the early stage under non-flooded mulching cultivation, but the situation was reversed at the later period. Both SM and PM rice reduced dry matter accumulation of shoot, but increased root dry weight, enhanced the remobilization of assimilates from stems to grains and increased the harvest index. During the middle and later grain filling period, mulched plants showed a faster decrease in chlorophyll concentrations, photosynthetic rates of flag leaves and root activity than TF rice, indicating that non-flooded mulching cultivation enhanced plant senescence. In comparison, SM treatment produced higher grain yield and, more dry matter accumulation and panicle numbers than the PM treatment. The overall results suggest that high yield of non-flooded mulching cultivation of rice can be achieved with much improved irrigaUonal water use efficiency.

Effect of various crop rotations on rice yield and nitrogen use efficiency in paddy–upland systems in southeastern China

To evaluate the effects of various rotation systems on rice grain yield and N use efficiency, a paddy–upland cropping experiment(2013–2016) was conducted in southeastern China. The experiment was designed using six different rice––winter crop rotations: rice–fallow(RF),rice–wheat(RW), rice–potato with rice straw mulch(RP), rice–green manure(Chinese milk vetch; RC–G), rice–oilseed rape(RO), and rice–green manure crop(oilseed rape with fresh straw incorporated into soil at flowering; RO–G) and three N rates, N0(0 kg N ha-1), N1(142.5 kg N ha-1), and N2(202.5 kg N ha-1). Average rice yields in the RF(5.93 t ha-1) rotation were significantly lower than those in the rotations with winter crops(7.20–7.48 t ha-1)under the N0 treatment, suggesting that incorporation of straw might be more effective for increasing soil N than winter fallow. The rice yield differences among the rotations varied by year with the N input. In general, the grain yields in the RP and RO–G rotations –were respectively 11.6–28.5% and 14.80–37.19% higher than those in the RF in plots with N applied. Increasing the N rate may have tended to minimize the average yield gap between the RF and the other rotations; the yield gaps were 18.55%, 4.14%, and 0.23% in N0, N1, and N2, respectively. However, the N recovery efficiency in the RF was significantly lower than that in other rotations, except for 2015 under both N1 and N2 rates, a finding that implies a large amount of chemical N loss. No significant differences in nitrogen agronomic efficiency(NAE) and physiological efficiency(NPE) were found between the rotations with legume(RC–G) and non–legume(RO and RW) winter crops, a result that may be due partly to straw incorporation. For this reason, we concluded that the return of straw could reduce differences in N use efficiency between rotations with and without legume crops. The degree of synchrony between the crop N demand and the N supply was evaluated by comparison of nitrogen balance degree(NBD) values. The NBD values in the RP and RW were significantly lower than those in the other rotations under both N1 and N2 rates. Thus,in view of the higher grain yield in the RP compared to the RW under the N1 rate, the RP rotation might be a promising practice with comparable grain yield and greater N use efficiency under reduced N input relative to the other rotations. The primary yield components of the RF and RP were identified as number of panicles m-2 and numbers of kernels panicle-1, respectively. The NAE and NPE were positively correlated with harvest index, possibly providing a useful indicator for evaluating N use efficiency.

Effect of Phosphorus and Irrigation Levels on Yield,Water Productivity,Phosphorus Use Efficiency and Income of Lowland Rice in Northwest Pakistan

With decreasing availability of water for agriculture and increasing demand for rice production, an optimum use of irrigation water and phosphorus may guarantee sustainable rice production. Field experiments were conducted in 2003 and 2004 to investigate the effect of phosphorus and irrigation levels on yield, water productivity （WP）, phosphorus use efficiency （PUE） and income of low land rice. The experiment was laid out in randomized complete block design with split plot arrangements replicated four times. Main plot consisted of five phosphorus levels, viz. 0 （P0）, 50 （P50）, 100 （P100）, 150 （P15o）, and 200 （P200） kg/hm2, while subplots contained of irrigation times, i.e. 8 （I8）, 10 （I10）, 12 （I12）, and 14 （I14） irrigation levels, each with a water depth of 7.5 cm. Mean values revealed that P150 in combination with I10 produced the highest paddy yield （9.8 t/hm2） and net benefit （1 231.8 US$/hm2） among all the treatments. Phosphorus enhanced WP when applied in appropriate combination with irrigation level. The highest mean WP [13.3 kg/（hm2-mm）] could be achieved at Plso with 18 and decreased with increase in irrigation level, while the highest mean PUE （20.1 kg/kg） could be achieved at P100 with I10 and diminished with higher P levels. The overall results indicate that P150 along with I10 was the best combination for sustainable rice cultivation in silty clay soil.

Moderate wetting and drying increases rice yield and reduces water use, grain arsenic level, and methane emission

To meet the major challenge of increasing rice production to feed a growing population under increasing water scarcity,many water-saving regimes have been introduced in irrigated rice,such as an aerobic rice system,non-flooded mulching cultivation,and alternate wetting and drying(AWD).These regimes could substantially enhance water use efficiency(WUE) by reducing irrigation water.However,such enhancements greatly compromise grain yield.Recent work has shown that moderate AWD,in which photosynthesis is not severely inhibited and plants can rehydrate overnight during the soil drying period,or plants are rewatered at a soil water potential of-10 to-15 k Pa,or midday leaf potential is approximately-0.60 to-0.80 MPa,or the water table is maintained at 10 to 15 cm below the soil surface,could increase not only WUE but also grain yield.Increases in grain yield WUE under moderate AWD are due mainly to reduced redundant vegetative growth;improved canopy structure and root growth;elevated hormonal levels,in particular increases in abscisic acid levels during soil drying and cytokinin levels during rewatering;and enhanced carbon remobilization from vegetative tissues to grain.Moderate AWD could also improve rice quality,including reductions in grain arsenic accumulation,and reduce methane emissions from paddies.Adoption of moderate AWD with an appropriate nitrogen application rate may exert a synergistic effect on grain yield and result in higher WUE and nitrogen use efficiency.Further research is needed to understand root–soil interaction and evaluate the long-term effects of moderate AWD on sustainable agriculture.

Rice Yield and Water Use as Affected by Soil Management Practices

A field experiment was conducted at the Shenyang Experimental Station ofEcology, Chinese Academy of Sciences, to study the effects of soil management practices on water useand rice (Oryza sativa L.) yield in an aquic brown soil during 2001 and 2002. A completely randomexperimental design with three replications was employed, having four soil management practices astreatments, namely: an undisturbed plow layer (CK), a thin plastic film (TN), a thick plastic film(TI) and subsoil compacting (CP). Results indicated no significant differences among all treatmentsfor rice biomass and grain yields. Also, water consumption was about the same for treatments TN andCK, however the treatments TI and CP were much lower with more than 45% and 40% of the irrigationwater in the treatments TI and CP, respectively, saved each year compared to CK. Therefore, wateruse efficiency was higher in the treatments TI and CP. These results will provide a scientific basisfor the water-saving rice cultivation.

Water Consumption Processes of Different Planting Models in Rice Production of Northeast China

Different irrigation schemes have different effects on water consumption in rice production.However,few studies have been conducted on the water consumption processes between dry direct seeding rice and transplanting rice under different irrigation schemes.Water consumption process,water use efficiency and correlation effect of water consumption on yield under different planting models in rice production were investigated in northeast China in 2018.Seven treatments were implemented:drip irrigation dry direct seeding rice(DDSR),wet irrigation dry direct seeding rice(WDSR),flooded irrigation dry direct seeding rice(FDSR),transplanting flooded rice(TFR),controlled irrigation transplanting rice(CTR),intermittent irrigation transplanting rice(ITR)and wet irrigation transplanting rice(WTR).Among them,TFR was the control.The results showed that the peaks of the water consumption amount,intensity and its modulus coefficient of the seven treatments all appeared in the middle tillering and the jointing booting stages.The total water consumption amount(ET)and average water consumption intensity of DDSR,WDSR,FDSR and WTR were lower than those of TFR,CTR and ITR.The maximum water use efficiency of yield(WUEy)occurred in DDSR with a value of 3.8 kg·m^(-3).WUEy of DDSR,WDSR and FDSR were significantly higher than those of TFR,CTR and ITR.In the middle tillering and the heading and flowering stages,the water consumption amount of each treatment had a positive effect on yield formation,and the water consumption amount in the late tillering stage had a negative effect on yield formation.The relationship between ET and yield(Y)of dry direct seeding and transplanting planting models showed a quadratic function curve.ET of transplanting planting model had a significant positive impact on Y,and ET of dry direct seeding planting model had no impact on Y.DDSR had the least total water consumption of 199.8 mm·m^(-2),the lowest water consumption intensity of 2.0 mm·d^(-1) and the greatest water use efficiency of 3.8 kg·m^(-3),which suggested that DDSR had the most significant water saving effect.The combination of dry direct seeding planting model and drip irrigation scheme would be a good option for determining a water-saving rice planting model in northeast China.

Rice Cultivation under Film Mulching Can Improve Soil Environment and Be Beneficial for Rice Production in China

Rice cultivation under film mulching is an integrated management technology that can conserve water, increase soil temperature, improve yield, and enhance water and nitrogen use efficiencies. Despite these advantages, the system does have its drawbacks, such as soil organic matter reduction and microplastic pollution, which impede the widespread adoption of film mulching cultivation in China. Nonetheless, the advent of degradable film, controlled-release fertilizer, organic fertilizer, and film mulching machinery is promoting the development of rice film mulching cultivation. This review outlines the impact of rice cultivation under film mulching on soil moisture, soil temperature, soil fertility, greenhouse gas emissions, weed control, and disease and pest management. It also elucidates the mechanism of changes in rice growth, yield and quality, water use efficiency, and nitrogen use efficiency. This paper incorporates a review of published research articles and discusses some uncertainties and shortcomings associated with rice cultivation under film mulching. Consequently, prospective research directions for the technology of rice film mulching cultivation are outlined, and recommendations for future research into rice cultivation under film mulching are proposed.

Photosynthetic Characteristics of Two Superhigh-yield Hybrid Rice

The photosynthetic functions and the sensitivity to photoinhibition were compared between two superhigh_yield hybrid rice (Oryza sativa L.) Liangyoupeijiu and X07S/Zihui 100, the newly developed from two parental lines and traditional hybrid rice Shanyou 63 developed from three parental lines. The results showed that, as compared to Shanyou 63, the net photosynthetic rate of Liangyoupeijiu and X07S/Zihui 100 was 9.1% and 11.9% higher, the transpiration rate was 37.4% and 31.4% lower, and their water use efficiency was 74.2% and 63.5% higher respectively. After strong light (2 000 μmol photons·m -2 ·s -1 ) treatment for 2 h, the photochemical quantum yield and the photochemical quenching increased by 37.0% and 18.0% respectively in Liangyoupeijiu, 28.3% and 46.2% in X07S/Zihui 100, but decreased a little in Shanyou 63. The non_photochemical quenching decreased in Liangyoupeijiu and X07S/Zihui 100 (about 50%) but increased greatly in Shanyou 63 (about 50%). Better photosynthetic functions, higher water use efficiency and stronger resistance to photoinhibition, may be the physiological basis for the super high_yield of the two hybrid rice under study.

Response of Photosynthesis, Growth, Carbon Isotope Discrimination and Osmotic Tolerance of Rice to Elevated CO_2

Four rice ( Oryza sativa L.) cultivars 'IR72', 'Tesanai 2', 'Guichao 2' and 'IIyou 4480' were grown in two plastic house (15 m×3 m) with 35 μmol/mol and 60 μmol/mol CO 2 concentration which was controlled by computer. As compared with rice at ambient 35 μmol/mol CO 2, the changes in photosynthetic rate at elevated CO 2 showed up_regulation ('IR72' and 'Tesanai 2'), stable (unchanged) in 'Guichao 2' and down_regulation type ('IIyou 4480'). Growth rate, panicle weight, integrated water use efficiency (WUE) calculated from Δ 13 C and the capacity of scavenging DPPH · (1,1_diphenyl_2_picrylhydrazyl) free radical were increased at elevated CO 2. An increment in total biomass was observed in three cultivars by elevated CO 2, with the exception of 'IIyou 4480'. Ratios of panicle weight/total biomass were altered to different extents in tested cultivars by elevated CO 2. When leaf segments were subjected to PEG osmotic stress, the electrolyte leakage rate from leaves grown at elevated CO 2 was less than that at 35 μmol/mol CO 2. Those intraspecific variations of rice imply a possibility for selecting cultivars with maximal productivity and high tolerance to stresses adapted to elevated CO 2 in the future.

Agronomic performance of drought-resistance rice cultivars grown under alternate wetting and drying irrigation management in southeast China

Compared to drought-susceptible rice cultivars(DSRs),drought-resistance rice cultivars(DRRs)could drastically reduce the amount of irrigation water input and simultaneously result in higher grain yield under water-saving irrigation conditions.However,the mechanisms underlying these properties are unclear.We investigated how improved agronomic traits contribute to higher yield and higher water use efficiency(WUE)in DRRs than in DSRs under alternate wetting and drying(AWD).Two DRRs and two DSRs were field-grown in 2015 and 2016 using two different irrigation regimes:continuous flooding(CF)and AWD.Under CF,no statistical differences in grain yield and WUE were observed between DRRs and DSRs.Irrigation water under the AWD regime was 275–349 mm,an amount 49.8%–56.2% of that(552–620 mm)applied under the CF regime.Compared to CF,AWD significantly decreased grain yield in both DRRs and DSRs,with a more significant reduction in DSRs,and WUE was increased in DRRs,but not in DSRs,by 9.9%–23.0% under AWD.Under AWD,DRRs showed a 20.2%–26.2% increase in grain yield and an 18.6%–24.5% increase in WUE compared to DSRs.Compared to DSRs,DRRs showed less redundant vegetative growth,greater sink capacity,higher grain filling efficiency,larger root biomass,and deeper root distribution under AWD.We conclude that these improved agronomic traits exert positive influences on WUE in DRRs under AWD.