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气候变化导致全球水分循环的改变,重塑了大部分地区的土壤-植被-大气连续体,增加了干旱发生的频率和持续时间[1]。目前,干旱已成为多数地区植物主要遭受的环境胁迫[2],而研究干旱对植物的作用机理,制定高效节水的灌溉策略成为当前人们的重要议题。
辽东栎(Quercus liaotungensis Koidz.)是我国华北中低山地带针阔叶混交林的建群树种[3]。随着气候变化加剧,土壤干旱成为辽东栎,尤其是辽东栎幼树生长的主要限制因素之一[4]。光合作用对干旱胁迫有明显的响应,其可以引发气孔限制(SL)或非气孔限制(NSL),亦或使2种限制的叠加出现,植物表现出多种干旱响应,例如:在光合系统的结构方面,气孔[5]、叶片表型特征[6]及叶绿体等超微结构[7]发生变化;在光合系统与环境的物质交换方面,气体交换参数[8]和叶片含水量发生变化[9];在光合系统的能量流动方面,用于抗氧化防御和非光化学猝灭的能量改变,光能利用效率随之变动[10]。目前,干旱胁迫对辽东栎幼树的表型生理特性、叶片气体交换、水分利用效率、木质部液流的影响已有研究报道[11-13],但对光合系统的影响机制仍然不清晰。
由于植物光合系统各组分对土壤干旱的敏感性不同[14],可以利用敏感性指标判断干旱程度。目前已有通过监测植物水势、叶绿素含量[15]、叶片反射光谱[16],叶片颜色信息[17]、叶温[18]、叶倾角[19]和叶片叶绿素荧光[20]判断干旱胁迫程度的研究。现有研究证实,叶倾角、叶片叶绿素荧光和光合气体交换参数均与植株含水量关联密切[21-23],但干旱胁迫下叶倾角与光合系统各组分之间的关联尚不清晰。鉴于此,本研究采用盆栽渐进式干旱胁迫法,以2年生辽东栎幼树为试材,研究干旱胁迫对辽东栎光合作用的结构、物质交换、能量流动等方面的影响机制,筛选干旱敏感性指标,为辽东栎高效灌溉提供理论依据。
渐进式干旱对辽东栎幼树光合特性的影响及敏感性分析
Effects and Sensitivity of Progressive Drought on Photosynthetic Characteristics of Quercus liaotungensis Seedlings
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摘要:
目的 探究辽东栎幼树叶片的光合系统对土壤渐进式干旱的响应,并筛选干旱敏感性指标。 方法 采用盆栽渐进式干旱胁迫法,对2年生辽东栎幼苗叶片的叶倾角、叶绿素荧光、光合作用等指标进行方差分析(ANOVA)和LOESS非线性拟合。 结果 渐进式干旱对光合气体交换的影响最显著,其次是叶倾角,最后是光系统II(PSII)的电子传递和能量耗散。依据土壤相对含水量(SRWC)对光合特性的影响,辽东栎幼树光合系统的干旱响应可划分为4个阶段:第1阶段(胁迫未发生,26%>SRWC>20%),光合气体交换参数无下降;第2阶段(中度胁迫,20%>SRWC>14%),气孔限制效应明显,叶倾角降低至−14.0 ± 1.7°;第3阶段(重度胁迫,14%>SRWC>8%),叶片水分利用效率(WUE)显著下降,叶倾角值降低至−43.2 ± 10.3°,光合气体交换明显减少,表明SRWC降低至14%是辽东栎幼树的灌溉临界值;第4阶段(极度胁迫,SRWC<8%),PSII的电子传递和能量耗散显著改变,光合机构严重受损,叶倾角值降低至−68.5 ± 6.7°,表明SRWC降低至8%是辽东栎幼树叶片的致死临界值。基于叶倾角对土壤干旱的响应存在阶段性差异,其可作为辽东栎幼树灌溉临界值的预警指标;PSⅡ单位面积有活性反应中心数量RCO/CS、单位反应中心吸收的能量ABS/RC、单位反应中心以热能形式耗散的能量DIO/RC、叶片性能指数PIABS可作为叶片致死的预警指标。 结论 本研究观察到辽东栎幼树叶片光合系统对土壤干旱的响应存在阶段性差异,据此确定了灌溉临界值和反映土壤干旱的敏感性指标,可以为辽东栎幼树高效灌溉策略的制定提供理论基础。 Abstract:Objective To investigate the response of photosynthetic system of leaves in Quercus liaotungensis seedlings under progressive drought and select drought sensitive indicators. Method Based on the progressive drought stress method in pots, we performed variance analysis (ANOVA) and LOESS nonlinear fit on leaf droop angle, chlorophyll fluorescence, and photosynthesis of 2-year-old Q. liaotungensis seedlings. Result The results indicated that progressive drought had the most significant effect on photosynthetic gas exchange, followed by leaf droop angle and electron transfer and energy dissipation of PSII. According to the influence of soil relative water content (SRWC) to photosynthetic characteristics, the drought response of the photosynthetic system of Q. liaotungensis seedling could be classified into four stages: Stage I (no stress, 26%>SRWC>20%), photosynthetic gas exchange parameters did not drop; Stage II (moderate stress, 20%>SRWC>14%), the effect of stomatal restriction was evident and the leaf droop angle was lowered to -14.0 ± 1.7°; Stage III (high stress, 14%>SRWC>8%), the water use efficiency (WUE) of leaf and the gas exchange parameters decreased significantly, and the leaf droop angle was lowered to -43.2 ± 10.3°, which indicated that SRWC lowered to 14% was the irrigation water threshold values for Q. liaotungensis seedling; Stage IV (extreme stress, SRWC<8%), the electron transport and energy dissipation of PSII changed significantly, the photosynthetic apparatus were severely damaged, the leaf droop angle was lowered to -68.5 ± 6.7° indicated that SRWC lowered to 8% was the lethal threshold for leaf of Q. liaotungensis seedling. Based on the stage differences in the leaf droop angle responses to soil drought, it could be used as the warning index of the irrigation water threshold value of Q. liaotungensis seedlings. The number of reaction centers per unit area in PSII (RCO/CS), the absorption flux per reaction center in PSII (ABS/RC), the flux of energy dissipated in processes other than trapping per active in PSII (DIO/RC), and the leaf performance index (PIABS) could be used as warning indexes of the lethal threshold for leaf. Conclusion In this study, the stage differences of the photosynthetic system of Q. liaotungensis seedling‘s leaf response to soil drought were observed, therefore determining the irrigation water threshold values and sensitivity indicators reflecting soil drought, which provides a theoretical basis for developing an efficient irrigation strategy for Q. liaotungensis seedlings. -
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