不同磷效率紫花苜蓿叶绿素荧光参数对低磷胁迫的响应

【目的】探讨不同磷效率紫花苜蓿(Medicago sativa L.)叶片光合性能对低磷胁迫的响应，从光能转化和利用的差异来揭示品种适应磷胁迫的机理。【方法】试验采用砂培法，供试材料为2个磷高效紫花苜蓿品种甘农6号(G6)、极光(JG)和2个磷低效品种Bara 310SC (B310)、甘农4号(G4)。以1/4霍格兰营养液为基础，设置磷浓度为0.5 mmol/L (正常对照)和0.05 mmol/L (低磷)两个处理水平，紫花苜蓿幼苗处理30天后，测定苜蓿幼苗叶片叶绿素荧光参数，将样品烘干后，测定生物量和磷含量。【结果】与对照相比，低磷胁迫下4个苜蓿品种的生物量和磷利用效率均降低，相对可变荧光诱导曲线J点和I点的荧光强度上升，初级醌受体(Q_A)被还原的最大速率(M_o)显著增加，受体库容量(S_m)等参数下降，PSⅡ受体侧受损；活性反应中心数目(RC/CS_o)降低，光能的吸收(ABS/RC、ABS/CS_o)、捕获(TRo/RC、TRo/CS_o)、传递(ETo...

Responses of chlorophyll fluorescence of alfalfa with various phosphorus utilization efficiencies to phosphorus deficiency

  【Objective】  This study was aimed to identify the effects of P deficiency on photosynthetic performance of alfalfa (Medicago sativa L.) and reveal the differences in light energy conversion and utilization among different varieties.  【Methods】  Sand culture method was used, two high-P-efficient varieties, Gannon 6 (G6), and Aurora (JG); and two low-P-efficient alfalfa varieties, Bara 310SC (B310) and Gannon 4 (G4) were selected as test materials. On the basis of 1/4 Hoagland solution, normal P control (0.5 mmol/L) and low P stress (0.05 mmol/L) solution were prepared. At the 30 days of culture, the chlorophyll fluorescence parameters of alfalfa leaves were measured, then the whole seedlings were harvested for the determination of biomass and P content.  【Results】  Compared with the control group, P deficiency decreased the biomass and P utilization efficiency of four alfalfa varieties, increased fluorescence intensity at points J and I of the relative variable fluorescence induction curve, increased the maximum rate of Q_A reduction (M_o) significantly, parameters such as receptor pool capacity (S_m) decreased and impaired the PSII receptor side; the number of active reaction centers (RC/CS_o) decreased, light energy absorption (ABS/RC, ABS/CS_o), capture (TR_o/RC, TR_o/CS_o), transfer (ET_o/RC) and dissipation (DI_o/RC, DI_o/CS_o) increased significantly, performance index (PI_abs and PI_total) decreased, photosynthetic electron transfer was hindered, and the overall performance of PSⅠ and PSⅡ decreased. In terms of the differences among varieties, the high-P-efficient varieties G6 and JG showed less variation in these parameters than the low-P-efficient varieties B310 and G4, and had higher biomass and P utilization efficiency under the same P treatment.  【Conclusion】  P deficiency mainly inhibits the performance of the electron transport chain on the acceptor side and reaction center of alfalfa leaves, which decreases the activity of PSⅠ and PSⅡ and hinders photosynthetic electron transport. These responses result in a reduction of biomass and P utilization efficiency. Compared to P-inefficient varieties, P-efficient varieties have higher photosynthetic electron transfer activity and more stable photosynthetic system. Among rapid chlorophyll fluorescence parameters, PI_abs is more sensitive to P deficiency, and shows a significant correlation with P utilization efficiency, which could effectively reflect the status of PSII light energy conversion efficiency, active reaction center and receptor side. All these indicate that PI_abs is an effective indicator for evaluating alfalfa photosynthetic performance under P deficiency.