土壤水分亏缺对陆地棉花铃期叶片光化学活性和激发能耗散的影响

EFFECTS OF WATER DEFICIT ON PHOTOCHEMICAL ACTIVITY AND EXCITATION ENERGY DISSIPATION OF PHOTOSYNTHETIC APPARATUS IN COTTON LEAVES DURING FLOWERING AND BOLL-SETTING STAGES

为了探讨水分亏缺对叶片光合机构光化学量子效率和非辐射热耗散的影响,在新疆气候生态条件下,采用膜下滴灌技术精确地控制滴水量,实现不同程度的土壤水分亏缺,系统测定了不同水分条件下陆地棉（Gossypium hirsutum）叶片叶绿素荧光参数、叶片接受光量子通量密度（Photon flux density,PFD）、叶片温度（Leaf temperature,Tleaf）以及叶片水势和叶绿素含量的变化。研究表明：轻度水分亏缺（田间持水量的55%-60%）叶片接受的PFD与对照（田间持水量的70%～75%）无差异,Tleaf略高于对照;中度水分亏缺（田间持水量的40%～45%）在12∶00（北京时间,下同）以前叶片接受的PFD和对照无差异,随后显著低于对照,Tleaf在整个日变化中均高于对照。不同水分处理对黎明前叶片PSⅡ最大光化学效率（The maximum photochemical efficiency of PSⅡ,Fv/Fm）没有影响。轻度水分亏缺叶片的实际光化学效率（PSⅡ photochemical efficiency,ΦPSⅡ）、表观电子传递速率（Electron transport rate,ETR）和光化学猝灭系数（Photochemical quenching,qp）的日变化与对照基本一致,非光化学猝灭系数（Non-photochemical quenching,NPQ）在12∶00以前和14∶00以后显著低于对照,在12∶00～14∶00和对照无差异。中度水分亏缺叶片的ΦPSⅡ、ETR和qp在12∶00才显著降低,此后由于叶片出现暂时萎焉、下垂,所接受的PFD减弱,叶绿素荧光参数缓慢恢复,且高于对照;NPQ在12∶00以前显著高于对照,14∶00略高于对照,此后低于对照。水分亏缺导致中午叶片水势和叶绿素a、叶绿素b含量降低,但叶绿素a/b比值升高。因此,在田间条件下,陆地棉可通过叶片萎焉下垂运动和叶绿素含量的变化调节叶片对光能的捕获,以及通过光合电子传递、热耗散水平的变化来适应水分亏缺的逆境。在中度水分亏缺条件下,陆地棉叶片萎焉下垂运动的被动调节减少了过量激发能对光合机构的伤害,保证了光合机构的正常运转。

Aims Cotton （ Gossypium hirsutum） is a major crop in Xinjiang Province, Northwest China. Because Xinjiang is characterized by deficiency of water resource and strong irradiance, study of water deficit on photoinhibition of cotton in this area is crucial not only for efficient irrigation, but also for physiological explo- ration of plant photo-protection strategy. Methods We investigated the effects of water deficit on physiological characteristics of cotton in the field. We measured diurnal variations of photon flux density （PFD）, leaf temperature （Tlea）, pre-dawn maximal photochemical efficiency of PS Ⅱ （Fv/Fm）, PS n photochemical efficiency （ ФⅡ ）, electron transport rate （ETR）, photochemical quenching （qp） and non-photochemical quenching （NPQ）, as well as chlorophyll content and water potential of cotton leaves subjected to different water supplies. Important findings Compared to control （70% - 75% of field capacity）, the diurnal variation of leaf incident PFD was similar and Tleaf was higher with mild water deficit （55% - 60% of field capacity）. The diurnal variation of leaf incident PFD with moderate water deficit （40% - 45% of field capacity） was similar be-fore fore 12：00 and then lower, as a result of leaf wilting than in the control. Leaf temperature with moderate water deficit was significantly higher than in the control during daytime. No significant effects were observed on predawn Fv/Fm; all values were between 0.83 and 0.84. There were no differences in diurnal variations of ФPSⅡ , ETR and qp between mild water deficit and control. However, NPQ with mild water deficit was similar before noon and then lower than file control. At 12：00, ФPSⅡ, ETR and qp, with moderate water deficit were significantly decreased and then recovered gradually to control values, possibly due to the decreased leaf incident PFD resulting from temporary and passive leaf wilting. However, NPQ with moderate water deficit was higher before 12：00 and similar at 14：00 but after that was lower than control. Water potential and chlorophyll content decreased with water deficits, but the Chl a/b ratio increased. All results showed that cotton leaves could acclimate to water deficit through changing leaf orientation and chlorophyll content to regulate light energy captured by leaves and changing electron transport rate and thermal dissipation ratio. We suggest that the risk of photosynthetic apparatus damage by excessive excitation energy could be decreased greatly through passive movement of cotton leaf wilting with moderate water deficit.