Study On The Effects Of Heat Stress At Booting Stage On Rice Growth And Yield Formation

Rice is one of the most important food crops in China,and its safe production is related to people's life and national stability.With the global warming,the greenhouse effect exacerbated,short-term extreme high temperature occurred frequently,which poses an increasing risk to rice production.Rice is particularly sensitive to high temperature,especially at the reproductive growth stages.Booting stage is the confluence of the vegetative growth and reproductive growth,the sensitivity to high temperature is just next to flowering stage.In this study,two cultivars with different heat tolerance,Nanjing 41(heat-sensitive)and Wuyunjing 24(heat-tolerant)were used for pot experiments.At the meiosis period of rice booting stage,the plants were moved to green house where the temperature was controlled according to diurnal variation curve.Four temperature regimes(Tmax/Tmin)were set at T1(32/22)?,T2(32/22)?.T3(32/22)?,and T4(44/34)were implemented for D1(2 days),D2(4 days)and D3(6 days)at booting stage.T1 was the control and the treatment duration was D2(4 days)only.By measuring the net photosynthetic rate,growth period,leaf area,chlorophyll content,organ carbon,nitrogen content,biomass and yield and its component,the effects of heat stress at booting stage on photosynthetic production,yield formation,carbon and nitrogen balance and source-sink relationship were studied.These results will provide guidance for the development of rice safety production management,the breeding of heat tolerance varieties and the improvement of anti-heat cultivation measures.The main results of this study are as follows:(1)Heat stress at booting stage affected the photosynthetic production and yield formation in rice.High temperature significantly advanced the flowering stage,while had no significant impact on the duration of filling.However,the extreme high temperature T4 delayed the flowering period and prolonged the duration of grain filling.During the treatment period,the transpiration rate,stomatal conductance and intercellular CO2 concentration under high temperature treatments increased while net photosynthetic rate decreased.After the heat stress treatments,the net photosynthetic rate,chlorophyll content and leaf area of the heat stress treatments were significantly different with the control in their recovery patterns.T3D3,T4D2 and T4D3 increased the shoot dry matter accumulation,but the other high temperature treatments decreased that.The longer of the high temperature,the less of the dry matter accumulation in spikes,the lower of the dry matter was transported from vegetative organs before anthesis and the more dry matter was accumulated in vegetative organs.The grain weight,grain number per spike and seed setting rate all got a significant decrease.Moreover,high temperature effects on the grain weight and seed setting rate of superior grains were significant.Overall,the high temperature at booting stage reduced the yield by decreasing the number of grains per panicle,and high temperature degree days(HDD)was negative linear and logistic relation with the grain weight and seed setting rate,respectively.(2)High temperature at booting stage had an effect on carbon and nitrogen balance and source-sink relationship in rice.The results showed that the high temperature at booting stage had no significant effect on leaf carbon content,but the carbon content in the panicle was significantly decreased and the carbon content in the spike was significantly increased.The nitrogen content of the leaves decreased at T2 and T3 at the booting stage,while at T3D3,T4D2 and T4D3 the content of nitrogen in the stem and the ear increased compared to the control.The high temperature at the booting stage would decrease the carbon and nitrogen transportation from the vegetative organs,and even the transportation did not occur.Carbon and nitrogen transportation in vegetative organs before flowering were quantified by HDD.The nitrogen accumutation linearly decreased and carbon accumutation increased as a logistic curve with the development days.In addition,the high temperature at booting stage also increased the C/N ratio of vegetative organs,and decreased the C/N ratio and grain/leaf ratio.The results also figured out that the C/N ratio had a good linear correlation with yield and net photosynthetic rate under high temperature treatment at booting stage.