臭氧胁迫对冬小麦光响应能力及PSⅡ光能吸收与利用的影响

Ozone stress on light response capacity and on the utilization of PSⅡ absorbed light energy of winter-wheat

为准确评价O3胁迫对冬小麦光响应能力和PSⅡ光能吸收、分配与利用的影响,通过OTC设置了活性碳过滤空气(CF,4—28 nL/L)、不通风(5H,15—68 nL/L)、环境空气(NF,7—78 nL/L)、100nL/L O3(CF100,96—108 nL/L)和150nL/L O3(CF150,145—160nL/L)等5种O3熏蒸处理,用IMAGING-PAM测量了冬小麦(丰抗13)扬花期的Fo、Fm及自然光下的快速光曲线。结果表明,O3胁迫显著降低了冬小麦PSⅡ的最大量子效率(Fv/Fm)、最大光合速率(Pm)、半饱和光强(Pm/α)、吸光系数(IA)、调节性热耗散的量子产额(Y(NPQ))和非光化学淬灭系数(NPQ),显著提高了冬小麦的初始光能利用效率(α)、非调节性热耗散的量子产额(Y(NO))和PSⅡ吸收光能的日累计损失(Daily∑Y(NO)+Daily∑Y(NPQ));CF处理显著提高了冬小麦的Pm、α、Y(NPQ)、NPQ及PSⅡ日累计利用的光能(Daily∑Y(Ⅱ));当其余4组的Y(NPQ)和NPQ趋于饱和时,NF仍在以较快的速率上升。O3胁迫显著降低了冬小麦吸收、利用光能的能力和光保护能力,改变了PSⅡ吸收光能的分配结构,提高了冬小麦对光强变化的敏感性,加剧了光抑制,致使冬小麦受到O3和过剩光能的双重伤害;CF处理下冬小麦的光合能力和光保护能力显著提高,但对强光的潜在耐受能力低于NF;固城的空气质量已对冬小麦造成一定影响,极可能导致产量损失。

Nowadays,ozone is considered to be the severest gaseous pollutant for plant productivity in many parts of the world,not only because of its heavy phytotoxicity but because of its concentration that had been increasing over the last century.Wheat is one of the most ozone-sensitive crops,with sensitivity differing between cultivars and cultivating modes of the same cultivar.Photosynthesis serves as a determinant of crop yield and plays a central role in botanical physiology,with the functional state as an idealized index of vigor and health of plants.Investigation of absorbed light energy utilization has become an important aspect of photosynthetic research.To explore ozone stress on light response capacity and utilization of PSⅡ absorbed light energy of winter wheat,experiment was conducted in Gucheng Ecometeorological Integrative Observation Experiment Station（39°08′N,115°40′E） of Hebei Province,with winter wheat seeds drilling sown in the OTCs（Open-Top Chambers） on October 17,2008 and the stands were exposed to charcoal filtered air at the steaming levels as follows： charcoal filtered air（CF,O3 ranging over 4—28 nL/L）,ambient air（NF,O3 ranging over 7—78 nL/L）,100 nL/L O3（CF100,O3 ranging over 96—108 nL/L） and 150 nL/L O3（CF150,O3 ranging over 145—160nL/L） between 17 March and 2 June 2009,and beside,a closed OTC（5H,O3 ranging over 15—68 nL/L） was set up for comparison.For these wheat stands the steaming was conducted between 9：00—17：00 BST each day,with the operation totaling 45 days except overcast and rainy weather till the flowering initiation.Thereafter the steaming continued for additional 22 days till harvest.And between 22：00 — 23：59 BST,5 May 2009 an IMAGING-PAM（H.Walz,Effeltrich,Germany） modulating fluorometer was used to measure the minimal and maximal fluorescence yield（denoted as Fo and Fm,respectively） after the stands adapted to darkness,with the measured zone marked by two vertical black lines as shown on leaf with a soft writing brush.Between 9：00—12：00 BST 6 May 2009 the light absorbing coefficient PAR-absorptivity（IA） and rapid light curves（RLC） were measured over the marked area.The above measurements were carried out in the following order： CF-1,5H-1,NF-1,CF100-1,CF150-1,CF-2,5H-2,NF-2,CF100-2,CF150-2,CF-3 followed by Fo and Fm exported to the related RLC-measured records by means of Imaging Win（IMAGING PAM software）,whereby are re-calculated the fraction of energy dissipated as heat via the regulated photoprotective NPQ mechanism and the fraction that is passively dissipated in the form of heat and fluorescence,designated as Y（NPQ） and Y（NO）,respectively at PSⅡ.Results indicate that CF100 and CF150 treatments remarkably decrease the maximum quantum yield of PSⅡ（Fv/Fm）,the largest capacity of photosynthesis（Pm）,half-saturation light intensity（Pm/α）,PAR-absorptivity（IA）,Y（NPQ） and non-photochemical quenching efficiency（NPQ） when photosynthetically active radiation（PAR） is more than 200μmol· m-2·s-1.With PAR below the level under the CF100 and CF150 treatments,the initial slope（α） of the RLC and quantum yield（Y[Ⅱ]） of photochemical energy conversion at PSⅡ are much larger than those from the NF treatment.In that case,the above figures decrease appreciably and so does the daily total utilization of light energy via photochemical conversion（Daily ∑Y（Ⅱ））,and the Y（NO） at PSⅡ agrees with the greatly increasing proportion of light energy lost via Y（NPQ） [daily ΣY（NPQ）] and Y（NO） [Daily ∑Y（NO）] approaches in the accumulative energy absorption at PSⅡ on a daily basis.The CF treatment increases greatly Y（Ⅱ）,Pm,α,Y（NPQ）,NPQ and Daily ∑Y（Ⅱ） for daily accumulated energy utilization at PSⅡ from photochemical reaction,with Y（NO） significantly lower than the others.The 5H treatment produces much lower Pm and Pm/α,compared to those from NF treatment.When the other 4 treatments-given Y（NPQ） and NPQ approach saturation,those related to NF treatment increase at higher rates.High-concentration ozone reduces pronouncedly light energy absorption,usability and protection against light damage to winter wheat,thereby changing the structure for distributing energy at PSⅡ,improving the sensitivity of the crop to change in light intensity and increasing light suppression so that the wheat is being damaged by twofold injuries by ozone and excess light energy.The CF treatment ameliorates the ability of photo-synthesis and-protection of the crop but makes the potential endurance of strong light reduced compared to the NF treatment.The 5H treatment-caused Pm and Pm/α decline may be owing to the lower content of CO2 in the OTC than in the others between 9：00—12：00 BST.The experiments were made in Gucheng station where air quality could have exerted some harmful impact,and the yield would suffer severest loss.