| The continusously rising atmospheric CO2 concentration and temperature have important effects on the growth and development of rice.Oryza sativa L.(rice)is one of the most important crops in the world.The elevated CO2 can enhance the photosynthesis,accelerate growth,and increase yield.Howerver,it is not clear whether and how these effects were regulated by environmental temperature,especially under natural farmland conditions.By using T-FACE(Temperature-Free Air CO2 Enrichment)facility,experiments on rice(Oryza sativa L.)cultivar ’Wuyunjing 23’ were conducted a field experiment with two levels of CO2(ambient and elevated CO2)and two temperature regimes(ambient and elevated temperature).The effects of elevated CO2 and temperature on the growth,yield formation,dry matter production and distribution,leaf photosynthesis and physiologic features,mineral nutrients were studied.The ultimate goal will be to assess temperature,CO2 interactions and influence factors and to provide the basis for predicting the variation in rice growth with changing climatic condition.The main results are listed below1.Compared with the ambient,elevated CO2(200 μmol·mol-1 above ambient CO2)leads to 2 days advance in heading and maturity stage of Wuyunjing 23,and about 0.5 days earlier in elevated temperature.Elevated CO2 increased grain yield by 13.6%on average of in two years,with 23.2%and 7.6%increase on ambient and elevated temperature in 2013,and 9.9%and 13.4%on ambient and elevated temperature in 2014.Elevated CO2 significantly increased panicle number per square meter,spikelet number per square metre,full-filled grain weight,blighted grain percentage,average grain weight by 13.2%,14.6%,2.6%,47.5%and 1.5%+,but significantly decreased full-filled grain percentage by 3.5%*,respectively.Elevated temperature significantly decreased grain yield by 7.9%,but had little influence on yield component factors.Significant interactions were detected between CO2 and temperature for panicle number per square mete,and interactions with different degree between CO2,temperature and year for panicle number per square mete,grain yield,full-filled grain weight and average grain weight.There was a statistically significant(0.01)in panicle number per square mete and(0.1)in grain yield between CO2 and year.2.Elevated CO2 increased above ground dry weight at jointing stage,heading stage,24 days after heading and maturity by 8.7%,9.8%,3.9%and 11.8%,respectively.A consistent trend of increase was detected on dry weight of leaf,stem and panicle at different growth stages respectively.Elevated CO2 showed no significant effects on dry matter distribution in leaves,stem,but signicant increased dry matter distribution in panicle.Elevated temperature increased above ground dry weight(+4.8%),dry weight and dry matter distribution of panicle signicantly,but had little effect on dry weight and dry matter distribution of leaf and stem.There were significant interactions between CO2 or temperature and growth stages on above ground dry weight,dry weight and dry matter distribution of panicle.Also significant interactions were detected between CO2 and growth stages for dry matter distribution of stem.3.The results of diurnal courses of photosynthesis in leaves showed that net photosynthetic rate(Pn)of rice on 61 days after transplanting(DAT)increased 38.5%by elevated CO2.The increment significantly reduced with the advance of the growth stages,and were even disappeared at the late grain-filling stage,similar to water use efficiency(WUE).A consistent trend of decrease was detected on stomatal conductance(Gs)and transpiration rate(Tr)at different time point on 75,92 and 109 DAT under elevated CO2,and the greatest reduction reached 14.2%and 4.9%for Gs and Tr,respectively.Elevated CO2 had no significant effect on the ratio of intercellular to air CO2 concentration(Ci/Ca)and stomatal limitation value(Ls)during the early rice growth season,but significantly increased Ci/Ca at the last three growth stages resulted in decreases in Ls.Average temperature increase of 1℃ had a positive effect on Pn,Gs,Tr and WUE at the early rice growth stages,but negative effects were found at the late grain filling stages.No clear CO2 by temperature interaction was detected for most of the measured photosynthetic traits except Pn on 61 DAT.The Pn response to elevated CO2 on 11:00,13:00 and 15:00 were similar,but on 9:00 and 17:00 were different greatly.4.The results of chlorophyll fluorescence parameters in leaves showed that Fv/Fm,ΦPS Ⅱ,qP on 32,47,76,91 and 108 DAT were increased by elevated CO2,concentration but decreased on 118 DAT.NPQ was decreased(-28.3%)significantly on 47 DAT,but increased on other growth period.The responses of Fv/Fm,ΦPS Ⅱ,qP and NPQ to elevated temperature were basically identical with that of elevated CO2.The intraction between CO2 and growth stages has a significant impact on the above parameters.There was a statistically significant(0.1)in Fv/Fm and ΦPS Ⅱ between CO2 and temperature,and qP between CO2,temperature and growth stages5.Elevated CO2 signifficantly increased the content of chlorophyll a,b,a+b of rice on 41,77 and 94 DAT.On the contrary,they were decreased by elevated CO2 on 110 and 119 DAT.The chlorophyll a/b ratio response to elevated CO2 was reverse.Little effect of elevated CO2 on leaf SPAD values was detected in the early and middle growth stages.But elevated CO2 decreased leaf SPAD values by 3.5%+and 19.1%**on 110 and 119 DAT.Elevated temperature had positive effects on chlorophyll a,b,a+b content in each growth stage of rice,but negative effects were found on chlorophyll a/b ratio.Little effect of temperature elevation on leaf SPAD values was detected in the early and middle growth stages.But temperature elevation significantly deceased leaf SPAD values by 7%-15%on last two growth stages.For the above parameters,significant CO2 or temperature by growth stages interactions were found6.Elevated CO2 significantly increased Vc,max,Jmax and TPU by 56.3%,49.3%and 21.2%on 59 DAT respectively,but almost decreased the on 77,93,108 and 119 DAT Vc,max,Jmax and TPU were decreased by elevated temperature at different growth stages,which Vc,max and Jmax significantly decreased by 13.8%and 12.1%on 119 DAT.There were significant interactions on the above parameters between CO2 and growth stages.7.Elevated CO2 significantly decreased Rubisco activity in leaves by 23.4%,30.2%,17.0%and 13.0%on 77,94,110 and 119 DAT,and reduced the RCA activity by 14.2%,9.1%,17.2%and 21.5%,which almost significant.The relative expression of rbcL,rbcS and CsRCA in leaves of different stages were also significantly reduced by elevated CO2 Elevated temperature had no significant effect on Rubisco and RCA activities,but almost increased relative expression of rbcL,rbcS and CsRCA.Significant interactions were detected on relative expression of rbcL between CO2 and temperature,Rubisco activity and relative expression of rbcL between CO2 and growth stages.8.It showed a decline trend on element concentration(N,P,K,Ca,Mg,Mn,Fe,Cuand Zn)of leaf,stem,panicle and plant of rice at different growth stages by elevated CO2.Elevated CO2 significantly increased the average of Ca concentration of plant by 9.2%,but decreased or stayed unchanged other element concentration.The element concentration response to CO2 was depond on rice organs,which the reduction of stem was the largest in most situation.Elevated CO2 slightly increased element accumulation at different growth stages.Elevated CO2 increased N distribution ratio at panicle by 12.2%,and decreased N and Ca distribution ratio at stem by 7.3%and 11.4%.There was no significant effect on other element istribution ratio at components of rice.In most cases,elevated temperature and intractions between temperature and CO2 or growth stages were no signicant effect on the above parameters.In conclusion,elevated CO2 make the rice growing period is reduced,but increased growth promotion,enhance the photosynthesis efficiency of rice,thereby enabling grain yield increased significantly.Both photosynthetic and fluorescence parameters of leaves indicated that photosynthetic adaptation occurred in rice under high CO2 concentration,which was mainly related to non-stomatal restriction such as the reduction of chlorophyll content,soluble protein content,Rubisco and RCA activity and down-regulated gene expression in leaves.In general,temperature increase of 1℃ had less effects on above paramenters than elevated CO2.Although there is no significant effect on growth,yield and photosynthetic parameters by CO2 and temperature,the intractions between them were affected by growth stages(such as partial photosynthetic parameters)and temperature of growing season(such as grain yield)in some degree. |
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