| In the context of global warming,extreme whether characterized by high temperatures has become one of the main factors that affect rice(Oryza sativa L.)yield and quality.In this regard,a study was conducted at the Agro-meteorological Experimental Station located in Nanjing University of Information Science and Technology during 2016-2017.The effects of distinct coping techniques on Liangyou 268 and Liangyoupeijiu rice varieties were examined using an artificial heating source(8:00-18:00,35±0.5?)or natural heat stress.In 2016,the optimum concentration of chemical preparations resistant to high temperatures and heat stress was screened by an artificial climate chamber control experiment and divided into the following four seeding setups:CK(irrigation with pond water,10 cm water layer maintained in the field,no heating),A1(irrigation with pond water,10 cm water layer maintained in the field,daily nighttime irrigation,heating),A2(irrigation with pond water,5 cm water layer maintained in the field,daily nighttime irrigation,heating),A3(irrigation with pond water,10 cm water layer maintained in the field,heating),CK(irrigation with pond water,10 cm water layer maintained in the field),31(irrigation with ground water,10 cm water layer maintained in the field,day and night times irrigation),B2(irrigation with pond water,10 cm water layer maintained in the field,day and night times irrigation),B3(Field does not contain water layer),CK(spayed with distilled water),Cl(20mmol·L 1CaC12 solution),C2(2.5mmol L-'Na2SiO3·9H20 solution),C3(22.04mmol L-1 KH2PO4 solution);CK(no distilled water spray),D l(8:00 distilled water spray),D2(12:00 distilled water spray),D3(14:00 distilled water spray.In 2017,the seeding setups were conducted:CK(irrigation with pond water,10 cm water layer maintained in the field,no heating),T1(irrigation with groundwater,10 cm water layer maintained in the field,diurnal irrigation and discharge),T3(irrigation with pond water,10 cm water layer maintained in the field,no discharge at night),and T4(22.04mmol'L-1KH2P04and 20mmol·L-1CaCl2·5H2O mixture solution).The main conclusions drawn from the experiment are as follows:1.High temperatures reduced the accumulation of dry matter,dry matter transport rate,material contribution rate and the proportion of dry matter at the heading stage,and increased the proportion of dry matter accumulation in stem and leaf and the total weight of dry matter in mature stage.The stem and sheath in mature period were also increased.In the experiment to study the effect of different irrigation depth on the remission of heat stress to rice,the CK did not suffer from heat stress.The proportion of dry matter accumulation,material transport rate,material contribution rate and the total weight of the upper part of the plant at maturity stage were CK>A1>A2>A3.In the experiment to study the effect of different irrigation water sources on heat stress of rice,all treatments were subjected to heat stress under natural conditions.The proportion of dry matter accumulation,material transport rate,material contribution rate and the total weight of the upper part of the plant at maturity stage were B1>CK>B3>B2.In the study of the effects of different chemical agents on the remission of heat stress,all treatments were heated by artificial auxiliary heating.The proportion of dry matter accumulation,material transport rate,material contribution rate and the total weight of the upper part of the plant at maturity stage wereCl>C3>C2>CK.In the study of heat stress heat damage at distinct time,all treatments were heated by artificial auxiliary heating.The proportion of dry matter accumulation,material transport rate,material contribution rate and total weight of spike in mature stage of each treatment were D2>>D3>D1>CK.The heat stress reduced the ratio of dry matter transport rate,material contribution rate and the proportion of dry matter in mature stage to the total weight of the top of the plant,resulting in the decrease of yield.Among the four technical measures,the highest yield was Al,B1,Cl and D2 respectively.The proportion of dry matter accumulation,dry matter transport rate,dry matter contribution rate and the total weight of the upper part of the plant in the mature period during 2017 were CK>T4>?T1>?T2>T3,whereas the the yield was CK>T4>T1>T2>T3.Thus implies that T4 treatment can alleviate the effect of heat stress heat damage on rice yield.2.Rice was exposed to heat stress at heading stage,and the activities of SOD,POD and CAT in leaves increased in a short time.However,their activities were significantly lower than those in CK after the natural temperature was restored by removal of heat stress.The heat stress accelerated the leaf senescence rate of rice by decreasing antioxidant enzyme activity,soluble protein content,net photosynthetic rate and SPAD.Results of the 2016 study elucidated that different technical measures could mitigate the damage of high temperature and heat injury on the photosynthetic and antioxidant enzyme systems of of rice sword leaf.The effects of different treatments in the four technical measures are CK>A1>A2>A3,B1>CK>B3>B2,C1?C3? C2?CK,D2?D3?D1?CK,respectively.It therefore implies that among the four technical measures,Al,B1,C1 and D2 had the best effect on reducing the rate of senescence of rice under high temperature and heat stress in 2016.Regarding 2017,the effect of different measures on rice photosynthesis and leaf antioxidant system under high temperature and heat stress were CK?T4?T1?T2?T3.This implies that the,T4 treatment could enhance the anti-aging ability of rice.3.Heat stress decreased total sugar content and increased nitrogen content in rice leaves and sheath.The total sugar content in the leaves and stem sheath of the four technical measures in 2016 were CK?A1?A2?A3,B1?CK?B3?B2,C1?C3?C2?CK,and the nitrogen content was the opposite.The total sugar content in the four measures in 2016 was A1,B1,C1 and D2 respectively.The highest nitrogen content was A3,B2,C2 and D1.In 2017,the contents of total sugars in leaves and stems and sheaths in different treatments ranged from CK?T4?T1 ?T2?T3,and nitrogen content was opposite.It is known that under high temperature,the absorption rate of nitrogen in rice is greater than that of carbohydrates,and the synthesis rate of grain protein is greater than that of starch.Therefore,under the high temperature condition,the carbon and nitrogen metabolism of T4 was the least affected.In summary,the effect of T4 treatment on the heat injury of high temperature is the best among the different countermeasures. |
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