施氮和供水对混播和单播白羊草叶片叶绿素荧光特性的影响

Effects of nitrogen applying and water supplying on leaf chlorophyll fluorescence characteristics of pure and mixed sowing Bothriochloa ischaemum

为明确干旱条件下混播和施氮对白羊草[Bothriochloa ischaemum(Linn.)Keng]叶片叶绿素荧光参数的影响,采用盆栽法并设置不同混播比例[白羊草与柳枝稷(Panicum virgatum Linn.)混播比例分别为8∶0、6∶2、4∶4和2∶6]、施氮水平(即不施氮和1 kg干土施0.1 g纯氮)和供水条件(即正常供水和干旱胁迫6 d后复水),对白羊草叶片叶绿素荧光参数的变化进行比较分析;在此基础上,采用一般线性模型分析这3个因素及其交互作用对白羊草叶绿素荧光参数的影响效应。结果显示:正常供水条件下,各处理组白羊草的最大光化学效率(F_v/F_m)、实际光化学效率(Φ_(PSⅡ))、表观光合电子传递速率(ETR)、光化学淬灭系数(qP)和非光化学淬灭系数(NPQ)均无明显变化。干旱及复水条件下,不施氮处理组白羊草的F_v/F_m值在干旱胁迫6 d(即土壤相对含水量最低)时降至最低值,并在复水2 d后恢复至与正常供水条件下相近的水平,而施氮处理组的F_v/F_m值则一直保持与正常供水条件下相近的水平;不论施氮与否,各处理组白羊草的Φ_(PSⅡ)、ETR、qP和NPQ值基本上均表现为在干旱胁迫6 d时达到最高值,并在复水2 d后恢复至正常供水条件下各参数值的90%以上。总体上看,混播白羊草的qP和ETR值均高于单播白羊草,而其NPQ值则低于后者。统计分析结果表明:混播比例、施氮水平和供水条件3个因素间的交互作用对白羊草的Φ_(PSⅡ)、qP和ETR值无显著影响,施氮水平对NPQ值的单独作用、施氮水平和混播比例的交互作用对F_v/F_m值以及施氮水平和供水条件的交互作用对ETR值也无显著影响,但这3个因素的单独作用及两两因素间的交互作用对白羊草其余叶绿素荧光参数均有显著或极显著影响。研究结果表明:一定程度的干旱胁迫有利于提高白羊草叶片PSⅡ反应中心的开放程度、光合电子传递速率和热耗散过剩光能的能力;在干旱胁迫条件下,施氮有助于白羊草叶片维持PSⅡ反应中心的活性和光化学效率;并且,与柳枝稷适度混播可改善白羊草叶片的光合性能,提高其种间竞争适应性。

In order to figure out the effects of mixed sowing and nitrogen applying on leaf chlorophyll fluorescence parameters of Bothriochloa ischaemum （ Linn.） Keng under drought condition,a pot-culture method was employed to compare and analyze the changes in leaf chlorophyll fluorescence parameters of B. ischaemum cultivated under different mixed sowing ratios （B. ischaemum mixed sowing with Panicum virgatum Linn, at the ratio of 8 ： 0,6 ： 2,4：4 and 2 -6, respectively）, nitrogen applying levels （no nitrogen applying and applying 0- 1 g pure nitrogen into 1 kg dry soil） and water supplying conditions （normal water supplying and rewatering after drought stress for 6 d）. On this basis,general linear model was used to analyze the influences of these three factors and their interaction on chlorophyll fluorescence parameters of B. ischaemum. The results show that there is no obvious change in the maximal photochemical efficiency （ Fv /Fm ）, actual photochemical efficiency （ΦPSⅡ）, apparent photosynthetic electron transport rate （ ETR）, photochemical quenching coefficient （ qP） and non-photochemical quenching coefficient （ NPQ） of B. ischaemum in all treatment groups under normal water supplying condition. Under drought and rewatering condition, Fv /Fm value of B. ischaemum in no nitrogen applying treatment group drops to the lowest value at drought stress for 6 d （ when soil relative water content is the lowest） , and is back to close level under normal water supplying condition at rewatering for 2 d, while Fv /Fm value in nitrogen applying treatment group is always near to the level under normal water supplying condition. Regardless of nitrogen application,ΦPSⅡ, ETR, qP and NPQ values in all treatment groups basically reach the highest value at drought stress for 6 d ,and restore to more than 9 0 % of all values under normal water supplying condition after rewatering for 2 d. In general, qP and ETR values of mixed sowing B. ischaemum are higher than those of pure sowing B. ischaemum,while NPQ value is lower than that of the latter. Statistical analysis result shows that interaction among three factors including mixed sowing ratio,nitrogen application level and water supplying condition has no significant effect on ΦPSⅡ, qP and ETR values of B. ischaemum, and single action of nitrogen application level on NPQ value, interaction between nitrogen applying level and mixed sowing ratio on Fv /Fm value,and interaction between nitrogen applying level and water supplying condition on ETR value are also not significant. However, single action and interaction between two factors of the three factors have significant or extremely significant effects on other chlorophyll fluorescence parameters of B. ischaemum. In conclusion, a certain degree of drought stress would be beneficial for enhancing open proportion, photosynthetic electron transport rate and heat dissipation for excess luminous energy of PSn action center in leaf of B. ischaemum ; under drought stress condition, nitrogen applying helps to maintain activity and photochemical efficiency of PSH action center in leaf of B. ischaemum ; and appropriately mixed sowing with P. virgatum can improve the photosynthetic performance of leaf of B. ischaemum and increase its interspecific competitive adaptability.