低氮胁迫对耐低氮玉米品种苗期光合及叶绿素荧光特性的影响

【目的】叶绿素荧光参数经常用来评价光合器官的功能和环境压力的影响,不同玉米基因型耐低氮胁迫能力差异较大,与光合及叶绿素荧光特性对低氮胁迫的响应机制有关。本文以耐低氮能力差异较大的4个玉米杂交种为试验材料,研究了低氮胁迫对不同耐低氮性玉米品种苗期光合及叶绿素荧光特性的影响,以期明确耐低氮胁迫玉米品种的光合机制。【方法】采用二因素完全随机设计盆栽试验,因素A为不同耐低氮性玉米品种:‘正红311’、‘成单30’和不耐低氮品种‘先玉508’、‘三北2号’;因素B为不同氮素水平:正常氮CK(霍格兰完全营养液,N 15 mmol/L)、低氮胁迫LN1(N 0.5 mmol/L)、极低氮胁迫LN2(N 0.05 mmol/L)。测定了苗期单株干物质积累量,单株氮素积累量,叶片叶绿素含量与荧光特性,以及光合效率指标。【结果】低氮胁迫下玉米苗期单株干物质积累量、单株氮素积累量、叶片叶绿素含量等生理指标显著下降,但耐低氮品种的下降幅度显著低于不耐低氮品种;低氮胁迫下玉米苗净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)显著降低,胞间CO2浓度(Ci)显著升高,净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)的降幅及胞间CO2浓度(Ci)的增幅耐低氮品种均显著低于不耐低氮品种;低氮胁迫下可变荧光(Fv)、最大荧光(Fm)、PSⅡ潜在活性(Fv/F0)、PSⅡ最大光化学效率(Fv/Fm)、PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P)等叶绿素荧光特性也均显著降低,耐低氮品种下降幅度显著低于不耐低氮品种;低氮胁迫下耐低氮品种PSⅡ实际光量子产量(ΦPSⅡ)降低,不耐低氮品种有所增加;而耐低氮品种非光化学猝灭系数(NPQ)升高,不耐低氮品种有所降低。【结论】耐低氮玉米品种能够减缓低氮胁迫对植株光合系统的影响,进而保证植株较高的氮素积累,提高叶片叶绿素含量,维持较高的PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P),为光合作用提供充足的光能;从而保持了较高的净光合速率(Pn),保证了耐低氮品种在低氮条件下保持较高的干物质生产。

Effects of low nitrogen stress on photosynthetic characteristics and chlorophyll fluorescence parameters of maize cultivars tolerant to low nitrogen stress at the seedling stage

【Objectives】Chlorophyll fluorescence parameters are often used to evaluate the function of photosynthetic organs and the influence of the environment pressure. Tolerance to low nitrogen stress are largely different with different maize genotypes, which can be reflected through photosynthesis and chlorophyll fluorescence characteristics. In this paper, the response of four maize cultivars to low nitrogen stress were compared at the seedling stage for the purpose of further understanding of the mechanism of their low nitrogen tolerance.【Methods】A completely random two-factor pot experiment was conducted in greenhouse. The main factor was maize cultivars, two tolerant cultivars of Zhenghong 311 and Chengdan 30, two non-tolerant cultivars of Xianyu 508 and Beisan 2; The second factor was N levels: N 15 mmol/L(CK, Hoagland nutrition solution), 0.5 mmol/L(low N stress, LN1), N: 0.05 mmol/L(extremely low N stress, LN2). The items were measured, including individual plant dry matter and nitrogen accumulation, relative chlorophyll content(SPAD)of leaves, and the photosynthesis parameters. 【Results】The dry matter and nitrogen accumulation amounts of per plant, relative chlorophyll content(SPAD)of leaves, net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), variable fluorescence(Fv), maximum fluorescence(Fm), potential activity of PSⅡ(Fv/F0), the primary maximum photochemical efficiency of PSⅡ(Fv/Fm), effective light quantum yield of PSⅡ(Fv′/Fm′)and photochemical quenching coefficient(qP)of the four maize hybrids are declined sharply under the low nitrogen stress conditions. Compared with the low nitrogen sensitive maize cultivars, the reduced ranges of these parameters of the low nitrogen tolerant maize cultivars are much lower. In contrast to the above parameters, the intercellular CO2 concentrations are remarkably increased in the tested maize hybrids, and the concentration increases of the low nitrogen tolerant maize cultivars are rather less than those of the sensitive ones. The actual photochemical efficiencies of PSⅡ in the light(ΦPSⅡ)of the low nitrogen tolerant maize cultivars are decreased, while those of the low nitrogen sensitive maize cultivars are increased. In addition, the non-photochemical quenching coefficients(NPQ)of the low nitrogen tolerant maize cultivars are increased, while those of the low nitrogen sensitive maize cultivars are decreased.【Conclusions】 The negative effect of N stress on the photosynthetic system of the low nitrogen tolerant maize cultivars can be offset to some extent, so a relatively high nitrogen accumulation is kept to improve chlorophyll content and maintain high effective light quantum yield of PSⅡ(Fv′/Fm′)and photochemical quenching coefficient(qP), and keep high net photosynthetic rate(Pn)to guarantee a higher dry matter productivity.