Effects Of Low Soil Temperature At Booting Stage On Physiology And Yield Of Water-saving Cultured Rice

【Object】The drip-irrigated rice has the significant advantages of water saving and high fertilizer efficiency.However,rice grower found that low temperature underground water(12-15 ℃)caused drip-irrigated rice yield decreased sharply,but with surface irrigation rice was affect not so severe.Therefore,in this study,the effects of chilling injury on the morphological characteristics and physiological and biochemical characteristics of rice under drip irrigation under mulch were investigated mainly by regulating the intensity and duration of soil low temperature under drip irrigation.The mechanism was clarified,which is of great significance to optimize the application of this technology.【Method】The experiment was conducted in 2016 and 2017 at the Key Lab of Oasis Ecology Agriculture of Xinjiang Production and Construction Group and at the Agricultural Experiment Station of Shihezi University.The rice variety in this study,T-43(Oryza sativa L.cv.T-43)has been recommended for use in drip-irrigated fields by the Tianye Agricultural Institute(Shihezi,China).The hydroponic experiment was conducted from March to July in 2016.A two-factorial design(water potential and duration of water stress)was adopted in the study.water potentialhas four levels: normal water conditions(CK)(0 MPa);W1(-0.02 MPa);W2(-0.05 MPa);W3(-0.1 MPa),and water stress durationlasted for 10 d(T1)and 20 d(T2)in the rice tiller stage.The osmotic potential of different waters is achieved by adding PEG-6000.The concentration of PEG-6000 is 0%,2.5%,5.0% and 7.5% according to the Michel formula(Michel,1973),respectively.After treatment finished,rice plant was transferred to normal nutrition solution(with no PEG addition).Each treatment was replicated four times.The soil temperature experiment was conducted in 2016 and 2017.The experiment included two irrigation methods(i.e.,FI and DI)and three soil temperatures(18,24,and 30°C,referred to as T1,T2,and T3,respectively).The T2,T3 treatment was favor soil temperature for rice growth.The T1 were cool treatment.The soil in the DI treatment was maintained at 90-95% of the soil water holding capacity,but never flooded.The water management in FI was maintained 2-5 cm above the soil surface.The soil temperature treatments began at panicle differentiation and continued for 10 d.after the treatment finished,the pots were transferred to greenhouse and grow in ambient temperature.Each treatment replicated three times.The low soil temperature experiment was conducted in 2016.The experimennt contained two-factorial design: irrigation method and low temperature duration time.soil temperature was controlled at 18℃;and low temperature duration S1: low soil temperature last for 10 days;S2: low soil temperature last for 20 days;S3: low soil temperature last for 30 days.Irrigation methods: drip irrigation(DI)and flooding irrigation(FI).The soil in the DI treatment was maintained at 90%-95% of the soil water holding capacity,but never flooded.The water level in FI was maintained 2-5 cm water floor above the soil surface.Each treatment replicated three times.The air relative humidity experiment was conducted in 2017.Two-factor: air relative humidity and irrigation method was designed in the experiment.Relative humidity treatment: CK: Normal room relative humidity(RH0)of greenhouse.RH1: Humidity control during rice heading and flowering stage 2 d.Bagging method was used to control the humidity around the spikelet.The water level in FI was maintained 4-5 cm above the soil surface.Irrigation method is drip irrigation or floodinig method.The soil in the DI treatment was maintained at 90%-95% of the soil water holding capacity,but never flooded.Each treatment was replicated three times.【Result】(1)The results showed drip-irrigated rice kept at 90–95% of field moisture capacity,is a mild water stress to rice.In the hydroponic experiment,the protective enzyme activity and soluble protein content in rice increased,but the growth rate and photosynthetic rate of CK and PEG 2.5(water potential between 0-0.05 MPa)were basically the same during the vegetative growth stage of rice.In the pot experiment,at soil temperature of 30°C,drip-irrigated rice significantly increased SOD activity by 5%,CAT activity by 23%,and proline concentrations by 27% and yield was decreased by 17.5% compared with flood irrigation.Therefore,drip irrigation rice is considered to be in a mild water stress environment.(2)Low soil temperature affects the photosynthetic and physiological characteristics of rice.In low temperature strength experiment,at low soil temperature of 18°C,drip irrigation significantly increased SOD activities by 7% and CAT activities by 23% compared with FI.Drip irrigation significantly reduced GA concentrations by 25% and IAA concentrations by 16% compared with flood irrigation.The ZR+Z concentrations were 13% less and ABA concentrations were 8% higher in drip irrigation than in flood irrigation at low soil temperature.In duration times experiment,after 20 d low temperature treatment,SOD,POD,CAT,Pro and MDA in drip irrigation rice significantly increased,especially SOD and CAT activities,but CAT activity decreased.Therefore,soil hypothermia exacerbates the physiological stress of drip-irrigated rice.(3)Low soil temperature reduces root water conductance,resulting in abortion of pollen.In the 18 °C soil temperature treatment,drip irrigation reduced rice root hydraulic conductivity by 58%,leaf water potential by 40% and leaf net photosynthesis by 25% compared with flood irrigation.Drip irrigation also increased leaf abscisic acid and proline concentrations by 26 and 40%,respectively.The starch concentration in male gametes was also 30% less in the drip irrigation treatment than in the flood irrigation treatment.Therefore,low soil temperature at the panicle stage aggravates the physiological water deficit under drip irrigation,leading to reduced starch content in male gametes and low fertilization rates.(4)Low soil temperature decreased the secondary branch and spikelet differentiation of rice,which led to a decrease in yield.In low temperature strength experiment,the negative effects of low-temperature treatment(18 °C)of drip irrigation rice were greater than flood irrigation,Compared with flood irrigation,drip-irrigated rice significantly reduced the amount of secondary spikelet differentiation,and pollen vitality decreased seriously,especially at 18 °C soil temperature,the pollen viability of drip-irrigated rice decreased by 8%;In duration times experiment,pollen vigor of the drip-irrigated rice generally declined.In soil low temperature at 30 days,the flood irrigation yield was 1.2 times than in drip-irrigated rice.Therefore,the main reason for the significant decrease in the yield of drip-irrigated rice caused by low soil temperature is that it affects the secondary branches and the differentiation of spikelets in rice.【Conclusion】Although drip irrigation provides a more stable water content for rice growth,it is still a(mild)drought stress environment relative to theflooding rice,but the soil hypothermia aggravates the rice stress to a certain extent.Soil hypothermia indirectly affected rice photosynthesis,which hindered the synthesis of starch and the pollination fertilization rate,led to the delay of spike differentiation of rice or the massive degradation or even abortion of spikelet.It also resulted in the imbalance of root and endogenous hormones in rice and the suppression of drip irrigation spikelet differentiation in rice eventually led to a significant reduction in yield.