不同供氮水平的核桃幼苗生长及叶绿素荧光特性

【目的】探讨核桃对缺氮胁迫的适应性及其机制。【方法】以核桃幼苗为研究对象,设置不同程度的缺氮处理:对照(CK)、中度缺氮(MN)和重度缺氮(SN),分析缺氮胁迫对核桃幼苗外部形态特征、生长情况及叶绿素荧光参数的影响。【结果】缺氮会使核桃幼苗失绿黄化,长势下降,地上部分和地下部分生物量、叶绿素a、叶绿素b和类胡萝卜素含量均显著低于对照,且总体随着缺氮程度加深和时间延长显著下降,尤其是处理后期(60~75 d)表现更明显;MN和SN处理下,核桃幼苗的光系统Ⅱ(PSⅡ)最大光化学效率(F_v/F_m)和光条件下PSⅡ天线转化效率(F_v'/F_m' )在前期(0~30 d)和后期(60~75 d)受影响较大,实际光化学效率(Φ_PSII)、电子传递速率(ETR)和光化学猝灭系数(qP)随胁迫程度加深明显下降,反之非光化学猝灭系数(NPQ)随胁迫程度加深而上升,且同样在处理后期(60~75 d)受影响较大;地上部分生物量与地下部分生物量、叶面积、根表面积、叶绿素a含量、F_v/F_m和ETR呈显著正相关,叶绿素a含量与叶面积、叶片厚度、F_v/F_m 和F_v'/F_m' 显著正相关。【结论】缺氮会抑制核桃幼苗对氮素的吸收和同化,阻碍根系生长,影响核桃幼苗对营养物质的吸收利用,导致植株矮小瘦弱、叶片变小、叶色变淡。在缺氮胁迫下,核桃光合色素含量下降也会造成叶绿体吸收光照的能力减弱,降低光合电子传递速率及对光能的利用效率,进而限制光合速率,影响植株生长。

Growth and chlorophyll fluorescence characteristics of walnut (Juglans regia) seedling under different nitrogen supply levels

【Objective】The adaptability of walnut (Juglans regia L.) to nitrogen deficiency and respective adaptive mechanisms were studied.【Method】Different nitrogen deficiency treatments, including a control (CK), moderate nitrogen deficiency (MN), and severe nitrogen deficiency (SN), were used to study the effects of nitrogen deficiency stress on morphological characteristics, growth, and chlorophyll fluorescence parameters of walnut seedlings.【Result】Nitrogen deficiency caused walnut seedlings to lose green but a show yellow coloration, and the growth was decreased. Biomass of the above-ground and below-ground parts, chlorophyll a, chlorophyll b, and carotenoid content were significantly lower compared to the control, and the decrease was more pronounced with the increasing nitrogen deficiency and over time, especially in the late treatment (60-75 d). The values of F_v/F_m and F_v'/F_m' of walnut seedlings treated subjected to MN and SN treatments were significantly affected at the early (0-30 d) and late stage (60-75 d). The actual photochemical efficiency (Φ_PSII), electron transfer rate (ETR), and photochemical quenching coefficient (qP) decreased significantly with the increasing stress, whereas the non-photochemical quenching coefficient (NPQ) increased with the increasing stress, and the effect was more pronounced in the late stage (60-75 d). The aboveground biomass was positively correlated with the belowground biomass, leaf area, root surface area, chlorophyll a content, F_v/F_m, and ETR, whereas the chlorophyll a content was positively correlated with the leaf area, leaf thickness, F_v/F_m, and F_v/F_m'. 【Conclusion】Nitrogen deficiency inhibits absorption and assimilation of nitrogen, hinders the root growth, and affects absorption and utilization of nutrients in walnut seedlings; as a result, the seedlings show dwarfism, weak growth, and smaller leaves with the brighter coloration. Under the nitrogen deficiency stress, the decrease in photosynthetic pigment content in walnuts can also reduce the ability of chloroplasts to absorb light and reduce photosynthetic electron transfer rates and the utilization efficiency of light energy, thereby limiting the photosynthetic rates and plant growth.