铅锌矿渣污染胁迫下苦楝光合-CO2响应过程及其模拟

Effects of Pb-Zn tailing on photosynthetic-CO2 response and its simulation in Melia azedarach tree

【目的】研究乡土树种苦楝Melia azedarach在铅锌矿渣污染胁迫下的光合-CO2响应过程,了解乡土树种在铅锌矿渣污染下生长适应潜力。【方法】设置对照(100%土壤)和铅锌矿渣按质量比添加的3种处理(10%矿渣+90%土壤、25%矿渣+75%土壤、50%矿渣+50%土壤),栽植苦楝一年后,测定并采用叶子飘的直角双曲线修正模型和FvCB生化模型模拟铅锌矿渣污染胁迫下苦楝光合-CO2响应过程。【结果】铅锌矿渣处理对苦楝叶片CO2响应过程影响显著,直角双曲线修正模型模拟发现铅锌矿渣的处理导致苦楝叶片初始羧化效率(CE0)、最大净光合速率(Pnmax)、CO2饱和点(Cisat)均显著下降,CO2补偿点(Cic)显著升高,且随矿渣处理水平的提高和时间的延长,影响程度逐渐增大。铅锌矿渣污染胁迫下苦楝叶片光合速率的下降主要由非气孔限制因素导致。FvCB模型模拟发现铅锌矿渣的处理导致苦楝叶片最大羧化效率(Vcmax)、最大电子传递速率(Jmax)、磷酸丙糖转运速率(Tp)和叶肉细胞导度(gm)显著下降,生化限制在苦楝叶片光合作用的下降中起到主导作用,铅锌胁迫抑制了Rubisco酶活性,特别是RuBP再生过程,使得苦楝碳同化能力受阻,相对生长率显著下降。直角双曲线修正模型相对直角双曲线和Michaelis-Menten模型拟合铅锌矿渣污染胁迫下的苦楝光合-CO2响应过程,决定系数高,适用性强。【结论】铅锌矿渣的处理对苦楝CO2响应过程产生了显著的影响,矿渣处理水平越高,时间越长,影响越严重。非气孔限制是导致苦楝叶片光合速率下降的主要原因,定量分析表明铅锌胁迫苦楝光合作用的降低主要归因于Rubisco酶活性下降,特别是RuBP再生过程受阻,造成碳同化过程出现障碍,气孔导度和叶肉导度对光合下降的也有一定的作用。最终苦楝的相对生长速率显著降低。本研究结果有望为重金属胁迫作用影响植物生长发育过程提供科学依据。

【Objective】To examine photosynthetic-CO2 process of Melia azedarach under the stress of Pb-Zn tailing residuals.Two aspects were to investigate:(a)fitting photosynthetic-CO2 response curves by using different models;(b)analyzing the effect of CO2 assimilation on photochemical process.【Method】Four Pb-Zn treatment levels of 100%soil(as control CK),10%tailing residual+90%soil(L1),and 25%tailing residual+75%soil(L2)and 50%tailing residual+50%soil(L3)were selected.One year after planting,CO2 response curve was measured based on net photosynthetic rate as a function of substomatal concentrations of ambient CO2 and modified model of rectangular hyperbola and FvCB biochemical model were used to simulate the photosynthetic-CO2 response process under stress of lead and zinc slag pollution.【Result】The treatment of Pb-Zn tailing residual has a significant effect on the CO2 response process of Melia azedarach.The modified model of rectangular hyperbola simulation found that the treatment of Pb-Zn tailing residual resulted in the initial carboxylation efficiency(CE0),maximum net photosynthetic rate(Pnmax),and CO2 saturation point(Cisat)both significantly decreased,the CO2 compensation point(Cic)increased significantly,and with the increase in slag treatment level and time,the degree of influence gradually increased.The decrease in photosynthetic rate of leaves under stress of Pb-Zn tailing residual pollution was mainly caused by non-stomata limiting factors.Maximum rate of Rubisco carboxylation(Vcmax),maximum rate of photosynthetic electron transport(Jmax),maximum rate of triose phosphate utilization(Tp)and mesophyll conductance(gm)were significant decreased by FvCB model.Biochemical restriction played a leading role in the decline of the photosynthesis of Melia azedarach leaves.Lead and zinc stress inhibited the activity of Rubisco enzyme,especially the regeneration process of RuBP,which hindered the carbon assimilation capacity of Melia azedarach and the relative growth rate decreased significantly.The modified model of rectangular hyperbola fits the photosynthesis-CO2 response process of Melia azedarach under Pb-Zn tailing residual pollution stress relative to the right-angle hyperbola and Michaelis-Menten model,and has a high determination coefficient and strong applicability.【Conclusion】The treatment of lead-zinc slag has a significant impact on the CO2 response process of Melia azedarach.The higher the slag treatment level,the longer the time and the more serious the impact.Non-stomatal limitation is the main reason for the decrease of photosynthetic rate of Melia azedarach leaves.Quantitative analysis shows that the decrease in photosynthesis of Melia azedarach seeds under lead-zinc stress is mainly due to the decrease of Rubisco enzyme activity,especially the inhibition of the regeneration process of RuBP,resulting in obstacles to the process of carbon assimilation,stomatal conduction degree and mesophyll conductance also play a role in the decline of photosynthesis.In the end,the relative growth rate of Melia azedarach significantly decreased.The results of this study are expected to provide a scientific basis for the effects of heavy metal stress on plant growth and development.