Effects Of Double-Stage Low Temperature Stress At Jointing And Booting On Development,Growth And Yield Formation In Wheat

Climate change has resulted in increased temperature variability,which will lead to more frequent occurrence of extreme low temperature events in the northern hemisphere.Spring low temperature events often occurred from late February to early April in the Huang-Huai winter wheat producing region,when most of winter wheat in this region is at jointing and booting stage,the possibility for winter wheat suffering multiple low temperature disasters is very high.Therefore,analyzing the effects of double-stage low temperature stresses on growth and yield of wheat can provide theoretical basis for making adaptive strategies under future climate change,and ensuring the safety of winter wheat production in China.In our study,two-year environment-controlled experiments under different low temperature levels at jointing stage(S1),booting stage(S2)and jointing-booting stage(Double-stage,S3)were conducted to compare the differences of wheat photosynthesis,biomass accumulation and partitioning,grain yield and yield components between single stage low temperature treatments and jointing-booting stage low temperature treatments,besides,to investigate the effects of low temperature stress at jointing-booting stage on growth,development and yield formation in wheat.The main results were as follows:Within a certain range of low temperature stress(The range of ACDD of Yangmai16:)5.4-28.29 ?.d;The range of ACDD of Xumai30:5.4-33.42 ?.d),During the low temperature treatment period(jointing,booting and jointing-booting stage),the photosynthetic parameters of Yangmail6 and Xumai30,including net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(GS),intercellular C02 concentration(Ci),relative chlorophyll content(SPAD),decreased with the decreasing low temperature levels.But,the intercellular CO2 concentration may be higher than controls under extreme low temperature level(T4S3).All photosynthetic parameters can recover to same status with check treatment within 7 days after low temperature stress treatment at jointing stage.However,photosynthetic parameters cannot fully recover after low temperature stress treatment at booting and jointing-booting stage,depending on the photosynthetic parameters and low temperature levels.All photosynthetic parameters of those two cultivars can return to normal status under T2 treatments,but cannot recover under T4 treatments.The responses of photosynthetic parameters after low temperature treatment under T3 treatments varied between cultivars and treatment stages.The effects of low temperature hardening at jointing stage differed between parameters and cultivars.For Pn,low temperature stress treatment at jointing only under T2 enhanced cold tolerance at booting stage in Yangmai16 and Xumai30.For Tr and Gs,enhanced cold tolerance at booting stage was observed for Xumai30 under T2 and T3 low temperature treatment at jointing stage,while no enhance of cold tolerance for Tr and Gs was found under all low temperature treatments at jointing stage for Yangmai16.For Ci and SPAD,there is no enhance of cold tolerance at booting stage after low temperature treatments at all three low temperature levels for two wheat cultivars.Leaf area and aboveground biomass from low temperature treatments decreased with the decreasing low temperature levels.Some of wheat tillers died after T3 and T4 treatments at jointing-booting and booting stage,which lead to the regeneration of tillers in later growth stage,and more regenerated tillers were observed under lower temperature treatments.Under the same low temperature level,larger leaf area from regenerated tillers were observed under low temperature stress at jointing-booting stage than booting stage.Under low temperature stress at the same stage,larger leaf area from regenerated tillers with T4 treatments than that with T3 treatments.The number of regenerated tillers increased gradually from flowering stage,and regenerated tillers grown slowly at its early period and accelerated growth rate during its late period.The regenerated tillers could partially compensate for the loss of the total dry matter due to low temperature stress.The loss of total dry matter under low temperature stress at booting stage can be alleviated with low temperature hardening with T2 treatments at jointing stage in Yangmail6,and with under T2.T3 and T4 treatments in Xumai30.Largest differences of partitioning indices for different organs between different low temperature treatments were found for low temperature stress at jointing-booting stage,then for low temperature stress at booting stage,while smallest differences found at jointing stage.Within a certain range of low temperature stress,as low temperature levels decreased,partitioning index for stem decreased,while partitioning index for leaf increased before flowering stage.After flowering stage,as low temperature levels decreased,partitioning index for stem increased,while the partitioning index for panicle decreased,and differences of partitioning index for leaf between different temperature treatments were reduced.Duration of green leaf area was prolonged because of the occurrence of the regenerated tillers under T3,T4 treatments at jointing-booting stage and T4 treatments at booting stage,which also resulted in the increase of s partitioning index for tem and green leaf during late growth period.The yield and yield components in both wheat cultivars decreased with decreasing temperature levels.Largest negative effects low temperature stress treatments on wheat yields was observed from treatments at jointing-booting stage,then from treatments at booting,and smallest negative effects were found from low temperature stress at jointing in both cultivars.The regenerated yield produced after the treatment of T3,T4 at jointing-booting and booting stage can compensate for the loss of grain yield of original spikes by 52.82%and 89.15%for Yangmai16 under jointing-booting stage stress,8.30%and 84.85%for Yangmai16 under booting stage stress,27.57%and 66.51%for Xumai30 under jointing-booting stage stress,and 14.65%and 83.16%for Xumai30 under booting stage stress.Low temperature hardening effects on grain yield could be found only from T2 treatments at jointing-booting stage in Yangmai16 and only from T2,T3,and T4 treatments at jointing-booting stage in Xumai30.The spike numbers,grain number per spike,and 1000-grain weight under low temperature stress at jointing-booting stage and single stages decreased with decreasing temperature levels.The contribution of spike numbers and grain number per spike to primary yield is larger than 1000-grain weight at different low temperature levels.Compared with 1000-grain weight and grain numbers per spike,spike numbers is more sensitive to low temperature stress.Grain number and grain weight from lower positions(1st-7th spikelets)in a spike were more sensitive than from upper positions(5th-top spikelets),then the middle positions(8th-14th spikelets).Also,larger effects of low temperature hardening at jointing stages were observed on grain weight and grain number from lower positions besides and upper positions than from middle positions.The yield and yield components were significantly negatively correlated with ACDD under all low temperature treatments.Within a certain range of ACDD,low temperature hardening at jointing stage could alleviate the loss of yield and yield components due to low temperature stress at booting stage.This study,by comparing the impacts of two-stage low temperature stress(jointing and booting)with impacts of low temperature stress at single stage,enriched the understanding about the effects of multiple low temperature stresses at jointing stage and booting stage,and confirmed the possibility of alleviating the effects of low temperature stress on yields at booting stage by low temperature hardening at jointing stage.The results are critical for making adaptive farming and cultivating practices under multiple low temperature stresses and developing simulation models to quantify multiple low temperature stresses effects on wheat development,growth and yield formation.