霍氏假单胞菌M11与巨大芽孢杆菌M28对低肥力胁迫下玉米光合特性调控机制的比较

Comparison of the regulatory mechanisms of photosynthetic characteristics in maize by Pseudomonas huaxiensis M11 and Bacillus megaterium M28 under low fertility stress

摘要:

目的 探究霍氏假单胞菌M11与巨大芽孢杆菌M28对土壤低肥力胁迫下玉米光合特性的调控作用及生理机制差异。方法 开展盆栽试验，设置正常土壤对照(control check, CK)、低养分处理(low nutrient treatment, LNT)及低养分接种处理(M11+LNT、M28+LNT)。于玉米抽雄期测定土壤养分、植株生长指标、气体交换参数、叶绿素荧光特性及快速叶绿素荧光诱导动力学(O-J-I-P chlorophyll a fluorescence transient, OJIP)曲线，于成熟期测定产量。结果 M11显著提高了土壤有效磷、速效钾和有机质含量，降低了电导率；M28显著提升了土壤全氮含量。2种接种处理均能显著促进玉米生长，提高株高、叶面积、SPAD值及生物量；极显著提升净光合速率(net photosynthetic rate, P_n)、气孔导度(stomatal conductance, G_s)、蒸腾速率(transpiration rate, T_r)和水分利用效率(water use efficiency, WUE)，降低胞间CO₂浓度(intercellular CO? concentration, C_i)。荧光参数显示最小荧光(minimal fluorescence, F_o)降低，最大光化学效率(maximum quantum yield of PSII, F_v/F_m)、实际光化学量子产量(actual quantum yield of PSII, Φ_PSII)、表观光合电子传递速率(electron transport rate, ETR)、光化学淬灭系数(photochemical quenching, qP)和基于激发能压力的光化学淬灭系数(fraction of open PSII centers based on excitation energy, qL)显著提高，非光化学淬灭系数(non-photochemical quenching, NPQ)无显著变化。OJIP曲线表明接种处理未出现K点，J点荧光降低，I点和P点荧光提高，相对可变荧光的差异动力学ΔV_t分析证实菌株同步优化光系统II (photosystem II, PSII)供体侧与受体侧的电子传递，I-P相振幅增大表明光系统I (photosystem I, PSI)活性增强。快速叶绿素荧光诱导动力学分析(junction-intermediate-peak test, JIP-test)参数显示，接种处理显著提高了以吸收光能为基础的性能指数(performance index based on absorbed light energy, PI_ABS)、以单位面积为基础的性能指数(performance index on a cross-section basis, PI_CS)、捕获的激子将电子传递到电子传递链中超过Q_A的其他电子受体的概率(probability that a trapped exciton moves an electron into the electron transport chain beyond Q_A, Ψ_o)、电子传递的量子产额(quantum yield for electron transport, φ_Eo)和单位反应中心捕获的用于电子传递的能量(electron transport flux per RC, ET_o/RC)，降低了单位反应中心耗散的能量(dissipated energy flux per cross-sectional area, DI_o/RC)和用于热耗散的量子比率(quantum ratio for dissipated energy, φ_Do)。最终，M11和M28处理使玉米鲜重较LNT组分别显著提高30.61%和22.64%。干重分别提高26.68%和23.41%。结论 M11主要通过提高土壤有效磷、速效钾含量直接优化能量代谢与气孔运动；而M28主要通过提升土壤全氮含量，侧重于稳定光合机构结构。二者共同保护光合机构完整性并优化光系统电子传递效率，显著增强了低肥力胁迫下玉米的光合性能与产量，为微生物菌剂在绿色增产中的应用提供了理论支持。

Abstract:

Objective To compare the regulatory effects and underlying physiological mechanisms of Pseudomonas huaxiensis M11 and Bacillus megaterium M28 on the photosynthetic characteristics of maize subjected to low soil fertility stress.Methods A pot experiment was implemented with four treatments: normal soil control (CK), low nutrient treatment (LNT), and bacterial inoculation under LNT conditions (M11+LNT, M28+LNT). At the tasseling stage, measurements were taken for soil nutrients, plant growth indices, gas exchange parameters, chlorophyll fluorescence characteristics, and the fast chlorophyll a fluorescence induction kinetics (O-J-I-P chlorophyll a fluorescence transient, OJIP curve). Yield components were assessed at physiological maturity.Results Inoculation with M11 significantly increased the content of available phosphorus, available potassium, and organic matter, while reducing the electrical conductivity in soil. M28 significantly enhanced the total nitrogen content. Both bacterial treatments significantly promoted maize growth, increasing the plant height, leaf area, SPAD value, and biomass. Moreover, they highly significantly enhanced the net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and water use efficiency (WUE), while reducing the intercellular CO₂ concentration (C_i). Chlorophyll fluorescence analysis revealed a decrease in minimal fluorescence (F_o) and increases in the maximum photochemical efficiency (F_v/F_m), actual photochemical quantum yield of PSII (Φ_PSII), apparent photosynthetic electron transport rate (ETR), photochemical quenching (qP), and the fraction of open PSII centers based on excitation energy (qL), with no significant change in non-photochemical quenching (NPQ). The OJIP curves indicated the absence of a K-step in inoculated plants, a decrease in fluorescence at the J-step, and increases at the I-step and P-step. The differential kinetic curves of relative variable fluorescence (ΔV_t analysis) confirmed that both strains synchronized the optimization of electron transport on both the donor and acceptor sides of photosystem II (PSII). The increased amplitude of the I-P phase suggested enhanced photosystem I (PSI) activity. Junction-intermediate-peak test (JIP-test) parameters demonstrated that inoculation significantly enhanced the performance index based on absorbed light energy (PI_ABS), the performance index on a cross-section basis (PI_CS), the probability that a trapped exciton moves an electron into the electron transport chain beyond Q_A (Ψ_o), the quantum yield for electron transport (φ_Eo), and the electron transport flux per reaction center (ET_o/RC). Conversely, dissipated energy flux per cross-sectional area (DI_o/RC) and quantum ratio for dissipated energy (φ_Do) decreased. Consequently, compared with the LNT group, the M11 and M28 treatments resulted in significant increases of 30.61% and 22.64% in maize fresh weight and 26.68% and 23.41% in dry weight, respectively.Conclusion P. huaxiensis M11 primarily enhances photosynthetic performance by increasing soil available phosphorus and potassium content, directly optimizing energy metabolism and stomatal movement, whereas B. megaterium M28 mainly acts by elevating soil total nitrogen content, focusing on stabilizing the structure of the photosynthetic apparatus. Together, they protect the integrity of photosynthetic apparatus and optimize the electron transport efficiency of photosystems, significantly improving the photosynthetic performance and yield of maize under low fertility stress. These findings provide a theoretical basis for the targeted application of microbial inoculants in sustainable agricultural production.