不同CO_2浓度升高水平对水稻光合特性的影响

Effects of Elevated CO_2 Concentration Levels on Photosynthetic Characteristics of Rice

CO_2浓度升高是全球气候变化的主要原因之一,同时CO_2是植物光合作用的原料,对植物的生长发育具有重要影响。研究水稻对不同CO_2浓度升高水平的响应,对于指导农业生产以及确保粮食安全具有重要意义。通过田间开顶箱试验,运用CO_2浓度自动调控系统研究不同CO_2浓度升高对水稻光合特性的影响。CO_2浓度设置3个水平:以背景大气CO_2浓度为对照(CK),在CK基础上分别增加40μmol·mol^(-1)(T_1)和200μmol·mol^(-1)(T_2)CO_2。利用Li-6400便携式光合作用测量系统,在关键生育时期测定净光合速率(Pn)、胞间CO_2浓度(Ci)、气孔导度(Gs)、蒸腾速率(Tr)和水分利用效率(WUE)等光合参数,并根据指数方程模型拟合最大净光合速率(Pn_(sat))、羧化效率(CE)、呼吸速率(R_p)和CO_2饱和点(CCP);使用元素分析仪测定叶片全氮含量。结果表明:在较低水平的CO_2浓度水平下,CK、T_1和T_2处理的Pn呈近似直线上升,随着CO_2浓度的升高Pn缓慢升高,当达到CO_2饱和点后趋于稳定。光合仪设定CO_2浓度为600μmol·mol^(-1)时,T_2在3个生育时期(拔节期、抽穗期和乳熟期)的Pn均较CK显著降低,降幅分别为44.0%(P<0.01)、43.4%(P<0.01)和49.1%(P<0.01);设定CO_2浓度为800μmol·mol^(-1)时,T2在3个生育时期的Pn较CK分别降低了4.9%(P=0.506)、12.7%(P=0.167)和16.6%(P=0.220);设定CO_2浓度为1 000μmol·mol^(-1)时,乳熟期T_2处理的Pn较T1显著降低,降幅为21.5%(P<0.05),表明水稻经过长时间的高CO_2浓度处理产生了光合下调。乳熟期T_2的Pn_(sat)和CE较T_1显著降低,降幅分别为21.3%(P<0.05)和29.1%(P<0.05)。此外,总光合速率和叶片氮含量存在极显著正比例函数关系(P<0.01),总光合速率随叶片氮含量的升高而升高。对照、T_1和T_2处理的WUE均随着光合仪设定CO_2浓度梯度的升高而增大;在同一设定CO_2浓度水平下,3种处理的WUE均无显著性差异。

The elevated CO2 concentration is one of main features of global climate change.As the raw material of photosynthesis,CO2 has an important influence on the growth and development of plants.Rice is one of the most important crops in the world,the study of crop response to different levels of CO2 concentration is of great significance for guiding agricultural production and ensuring food security.To investigate the effects of elevated CO2 concentration levels on photosynthetic characteristics of rice,field experiments with simulating elevated CO2 concentration were conducted by open-top chambers(OTCs)using a CO2 concentration automatic control system to achieve different levels of elevated CO2 concentration.The experimental treatments included the ambient CO2 concentration(CK),40μmol·mol-1 above ambient CO2(T1),200μmol·mol-1 above ambient CO2(T2).The data of net photosynthetic rate(Pn),intercellular CO2 concentration(Ci),stomatal conductance(Gs),transpiration rate(Tr),water use efficiency(WUE)were measured using a Li-6400 portable photosynthesis system.The key photosynthetic parameters including maximum photosynthetic rate(Pnsat),carboxylation efficiency(CE),light respiration rate(Rp),CO2 compensation point(CCP)were fitted and estimated according to the exponential equation model.The nitrogen content of leaves was determined by using the Element Analyzer.The results showed that Pn increased rapidly under the relatively lower CO2 concentration ranges and then increased slowly to the maximum value.When CO2 concentration arrived at the saturation point,Pn tended to be stable.At the CO2 concentration of 600μmol·mol-1,compared to CK,T2 treatments significantly reduced Pn by 44.0%(P<0.01),43.4%(P<0.01)and 49.1%(P<0.01)at the jointing,heading and milking maturity stages,respectively.At the CO2 concentration of 800μmol·mol-1,compared to CK,T2 treatments significantly reduced Pn by 4.9%(P=0.506),12.7%(P=0.167)and 16.6%(P=0.220)at the milking maturity stage.At the CO2 concentration of 1 000μmol·mol-1,compared to T1,T2 treatments significantly reduced Pn by 21.5%(P<0.05)at the milking maturity stage.The photosynthetic acclimation appeared in rice leaves under T2 treatment.Compared to T1,T2 treatments significantly reduced Pnsat and CE by 21.3%(P<0.05)and 29.1%(P<0.05),respectivley.The total photosynthetic rate was significantly and positively correlated with the leaf nitrogen content(P<0.01),and increased with the increase of the leaf nitrogen content.WUE of different treatments increased with the elevated CO2 concentration,CK,T1 and T2 treatment had no significant effect on WUE at the same CO2 concentration.