野生酸枣光合及叶绿素荧光参数对土壤干旱胁迫的响应

Responses of Photosynthesis and Fluorescence of Ziziphus jujuba var. spinosato Soil Drought Stress

为探究鲁中地区自然条件下野生酸枣光合生理参数对土壤逐渐干旱的响应机制,明确其与土壤水分的定量关系。该研究以2年生野生酸枣盆栽苗为实验材料,采用人工给水和自然耗水相结合法模拟自然条件下土壤干旱过程,分析野生酸枣叶片光合作用和荧光参数对土壤水分含量(RWC)的响应过程及其机制。结果表明:(1)野生酸枣叶片气体交换参数净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)均随着土壤含水量的增加表现出先升高后降低的趋势。当RWC<38.5%时,P_n下降,而胞间二氧化碳浓度(Ci)上升,气孔限制值(L_s)下降,叶片光合速率下降主要是非气孔限制因素所致;当RWC在38.5%~65.1%范围内,野生酸枣P_n下降,伴随C_i、气孔导度(G_s)均降低,野生酸枣叶片光合速率下降处于气孔限制阶段。(2)通过P_n和WUE对土壤水分的阈值模拟,发现维持野生酸枣叶片具有较高光合生产力的土壤水分范围为46.0%~0.5%,维持其较高水分利用效率的水分范围为56.3%~73.9%。(3)在土壤逐渐干旱过程中(RWC范围为29.9%~86.5%),野生酸枣最大荧光(F_m)、PSⅡ最大光化学效率(F_v/F_m)、PSⅡ实际光化学效率(ΦPSⅡ)逐渐降低,初始荧光(Fo)显著升高,光化学猝灭(qP)先升高再降低,非光化学猝灭(NPQ)在过高(RWC>83.7%)或过低(RWC<38.5%)的土壤水分下呈现较高值,表现出热耗散增加。研究认为,野生酸枣叶片气体交换参数及叶绿素荧光参数对土壤水分均具有明显的阈值响应,阈值点的土壤相对含水量大约为38.5%,低于阈值时叶片光合速率由气孔限制转向非气孔限制,PSⅡ受到损伤,电子传递受阻,光合机构受到破坏。

We explored the response mechanism of photosynthetic physiological parameters of wild Ziziphus jujuba var.spinosato soil drought under the natural condition in the area of central and southernShandong Province,and the quantitative relationship between the change process,mechanism and soil moisture under different water gradients.This paper studied wild Z.jujuba var.spinosa seedlings of 2 years old,and by artificial water supply and natural water consumption to simulate the soil drought under natural condition,studied the response process and mechanism of photosynthesis and fluorescence parameters of wild Z.jujubavar.spinosaleaves to the soil moisture（RWC）.The results showed the following.（1）The gas exchange parameters in leaves of wild Z.jujubavar.spinosa which is the net photosynthetic rate（Pn）,transpiration rate（Tr）and water use efficiency（WUE）were increased firstly and then decreased with the increase in soil water content.When the RWC 38.5%,the net photosynthetic rate（Pn）and the stomatal limitation（Ls）were both decreased,while,the intercellular CO2 concentration（Ci）was increased,which indicated that the decline of the photosynthetic rate of the leaves was mainly caused by non-stomatal limitation.When RWC = 38.5%-65.1%,the net photosynthetic rate（Pn）was decreased,the intercellular CO2 concentration（Ci）and stomatal conductance（Gs）were both decreased,and the photosynthetic rate of the leaves was also decreased in leaves of Z.jujubavar.spinosaat stomatal limitation stage.Therefore,the decline of the photosynthetic rate of wild Z.jujuba var.spinosais about RWC=38.5% from the stomatal limit to the non stomatal limit.（2）The soil water content in leaves of wild jujube leaves with high photosynthetic productivity was 46.0%-80.5% by threshold simulation of Pnand WUE,and that of higher water use efficiency was 56.3%-73.9%.（3）In the process of soil drought（RWC range of 29.9%-86.5%）,the maximum fluorescence（Fm）,the maximum photochemical efficiency of PSⅡ（Fv/Fm）,and the PSⅡ actual photochemical efficiency（ΦPSⅡ）gradually decreased,the initial fluorescence（Fo）was significantly increased,the photochemical quenching（qP）was increased first and then decreased,the Non-photochemical quenching（NPQ）was exhibited higher values with the excess or low of the soil moisture（RWC 83.7%;RWC 38.5%）,which showed that the heat dissipation of Z.jujubavar.spinosa was increased.The results showed that the parameters of gas exchange and chlorophyll fluorescence in leaves of wild Z.jujuba var.spinosa have obvious threshold response to soil moisture,and the RWC was about 38.5% at the threshold point.When RWC 38.5%,the photosynthetic rate of the leaves changed from stomatal limitation to non-stomatal limitation,the PSⅡof wild Z.jujuba var.spinosa was damaged,the electron transport was blocked and the photosynthetic mechanism was destroyed.