李 麗, ?？》? 文 志, 崔 健, 王效科,*

1 中國科學(xué)院生態(tài)環(huán)境研究中心城市與區(qū)域國家重點實驗室, 北京 100085 2 中國科學(xué)院華南植物園, 廣州 510650 3 中國農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所, 北京 100081

干旱和臭氧濃度升高對元寶楓早生和晚生葉片色素和脫落酸含量的影響

李 麗1, ?？》?, 文 志1, 崔 健3, 王效科1,*

1 中國科學(xué)院生態(tài)環(huán)境研究中心城市與區(qū)域國家重點實驗室, 北京 100085 2 中國科學(xué)院華南植物園, 廣州 510650 3 中國農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所, 北京 100081

臭氧和干旱是威脅我國北方城市植物生長的兩大重要因素。于2012年利用開頂式氣室,通過設(shè)置4個處理(AW-大氣環(huán)境和水分充足；AW+60-大氣增加60 nL/L臭氧+水分充足；AD-大氣+干旱處理；AD+60-大氣增加60 nL/L臭氧+干旱處理),開展了大氣臭氧濃度升高(以下簡稱“臭氧”)和干旱對元寶楓秋季變色期主要色素含量及脫落酸(ABA)含量的影響研究。結(jié)果表明：(1)早生葉在臭氧處理后,總?cè)~綠素和類胡蘿卜素分別下降了21%和29.6%、花青苷和類黃酮相對含量顯著升高了34.1%和7.3%、脫落酸含量增加了19.8%。干旱處理后,早生葉總?cè)~綠素顯著下降了18.7%、花青苷和類黃酮相對含量分別顯著升高了37%和7.4%、脫落酸含量顯著升高了13%。葉片的上述生理變化將會導(dǎo)致葉片提前變紅、葉片早衰和提前脫落。(2)晚生葉在干旱處理后總?cè)~綠素含量減少了18.8%,脫落酸含量增加了33.4%,臭氧以及與干旱共同處理未對晚生葉產(chǎn)生顯著影響。(3)臭氧和干旱共同處理后,早生葉總?cè)~綠素含量、花青苷和葉片脫落酸含量存在顯著交互作用,交互作用緩解了葉片總?cè)~綠素的下降和花青苷的上升,但未緩解葉片脫落酸含量的增加。綜上,早生葉和晚生葉對臭氧和干旱處理的響應(yīng)不同,早生葉對臭氧處理響應(yīng)大于晚生葉,而晚生葉對干旱更敏感。臭氧和干旱處理均加速了葉片衰老,二者共同處理后葉片脫落風(fēng)險增加。

元寶楓；臭氧；干旱；光合色素；花青苷；類黃酮；脫落酸

臭氧是一種重要的具有氧化性的污染氣體,過高的濃度會威脅植物的生長、農(nóng)作物產(chǎn)量及人類健康[1- 2]。由于化石燃料的使用和城市化的快速發(fā)展,大量臭氧前體物體NOx被排放到大氣中,導(dǎo)致了我國各大城市空氣中臭氧濃度不斷升高[3- 5]。據(jù)文獻報道,2012年北京城郊7—8月份臭氧極值達到195.8 nL/L[6],如此高的臭氧濃度將會對植物生長造成傷害,如葉片出現(xiàn)黃褐色、黑色或紫紅色集中于葉脈兩側(cè)的密集斑點,在北京城區(qū)及郊區(qū)已發(fā)現(xiàn)多種植物葉片受害癥狀[6-7]。同時,干旱也是限制我國北方樹木生長的重要因素。在全球氣候變化背景下,頻繁出現(xiàn)的干旱和不斷升高的大氣臭氧濃度將會共同對城市樹木生長產(chǎn)生嚴重威脅,增加了植物響應(yīng)的不確定性和復(fù)雜性。

葉片色素含量對植物生長具有重要意義。葉綠素和類胡蘿卜素不僅是主要的光合色素,同時也與花青苷和類黃酮共同參與調(diào)節(jié)葉片顏色,葉片葉綠素和類胡蘿卜素的降解,花色素苷的積累,使元寶楓等彩葉樹的葉片在秋季由綠色轉(zhuǎn)為紅色[8-9]。因此葉片秋季色素含量和脫落酸含量的變化能夠反映著葉片秋季變色的時間和長度,也影響著城市的秋季景觀。已有研究表明,臭氧會通過植物氣孔進行葉片內(nèi)部,直接攻擊原生質(zhì)膜上的類脂或蛋白質(zhì),造成光合色素合成降低,葉綠素分解[10-11]。花青苷是一種水溶性的黃酮多酚類化合物,是秋季紅葉植物呈現(xiàn)紅色的主要色素,也是一些彩葉樹種葉片衰老的標志[12-13]。類黃酮也是植物體內(nèi)重要的色素,用于吸收UV-B,調(diào)控葉片顏色和亮度[14-15]?；ㄇ嘬站哂泻軓姷目寡趸?能夠清除臭氧等污染物導(dǎo)致的活性氧自由基,一些研究結(jié)果表明臭氧濃度升高后葉片花青苷和類黃酮的含量增加[16-17]。因為花青苷具有水溶性,干旱脅迫后葉片花青苷含量上升以降低細胞滲透勢[16,18]。但目前對臭氧和干旱復(fù)合影響植物葉片花青苷和類黃酮的研究還很少。

元寶楓(AcertruncatumBunge)是我國特有的槭樹科落葉喬木,因其秋季葉片鮮艷的紅色,葉片能夠吸附粉塵,苗木易栽培等特點在北方城市廣泛種植,是重要的具有觀賞價值,生態(tài)和經(jīng)濟價值的城市綠化樹種。目前對于秋色葉樹種-元寶楓葉色表達影響的研究有光照影響[19],K元素影響[20],季節(jié)變化[21],溫濕度及外源蔗糖[9]以及轉(zhuǎn)色機理[8]研究等,目前未見有關(guān)于元寶楓色素含量對于大氣污染物臭氧,干旱及其協(xié)同作用響應(yīng)的相關(guān)研究。

本研究選擇一年生元寶楓幼苗為研究對象,于2012年在北京市昌平區(qū)利用開頂式氣室,設(shè)置兩個臭氧濃度和兩個水分梯度,對葉片總?cè)~綠素、花青苷和類黃酮相對含量以及葉片脫落酸含量進行了測定。本實驗?zāi)康氖茄芯砍粞鯘舛壬吆透珊祵υ獙殫魅~片的主要色素和脫落酸含量的變化,為評價我國北方城市面臨的大氣污染和干旱共同對樹木生長影響提供數(shù)據(jù)支持,研究結(jié)果對于模擬和預(yù)測未來氣候變化對城市樹木生長及觀賞價值影響具有重要意義。

1 材料與方法

1.1 實驗地點

實驗地點位于北京市昌平區(qū)種子管理站(40°12′N,116°08′E),屬暖溫帶大陸性季風(fēng)氣候,年均降水量為550.3 mm[22]。土壤類型為潮土,質(zhì)地為砂壤,有機質(zhì)含量為16.4 g/kg,全氮0.9 g/kg,速效磷38.1 mg/kg,速效鉀102.1 mg/kg,pH 8.3。

1.2 實驗設(shè)計和實驗材料

實驗在開頂式氣室內(nèi)進行,氣室的設(shè)計在之前的基礎(chǔ)上有所改進[5]。氣室材料為陽光板(透光率85%),形狀為圓柱體 (直徑2 m,高2.5 m),頂部有高于頂端的透明擋板用于防止雨水進入,罩子內(nèi)外氣體自由流通,每個罩子周圍挖有25 cm寬,75 cm深的水溝,內(nèi)鋪設(shè)透明薄膜用于防止外部雨水進入以及內(nèi)外水分交換。共12個罩子,每兩個之間的距離為2 m (開頂式氣室及細節(jié)描述見文獻[10])。實驗設(shè)置4個處理,分別為：AW-大氣臭氧+水分充足,AW+60-大氣增加60 nL/L臭氧+水分充足,AD-大氣臭氧+干旱,AD+60-大氣加60 nL/L臭氧+干旱。共12個開頂式氣室,每個處理3個重復(fù),因此每個罩子為1個重復(fù)。干旱設(shè)置為土壤田間持水量的50%,實驗開始后所有罩子停止?jié)菜?待土壤水分下降到相同值后進行不同水量灌溉。通過土壤水分(EC- 5,Decagon Device,UK)和土壤水勢(MPS- 2,Decagon Device,UK)監(jiān)測,定量澆水的方法控制干旱。對照處理土壤水分為田間持水量,不存在干旱脅迫。臭氧熏氣時間為7月28日開始,10月25日結(jié)束,每天熏氣時間8:30—17:30,陰雨天氣停止熏氣,總處理時間為57d,熏氣期間大氣臭氧均值為34 nL/L,臭氧累計量AOT40為28.2 μL L-1h。

實驗材料為1年生元寶楓(Acertruncatum)幼苗,由北京本地苗圃購入,2012年4月份移栽到氣室外緩苗,5月30日選取長勢一致的120株幼苗移入開頂式氣室內(nèi)進行適應(yīng),每個罩子內(nèi)種植10株元寶楓。每個罩子內(nèi)種植10株元寶楓。為避免花盆限制根系生長,幼苗直接種植于開頂式氣室內(nèi)。元寶楓為落葉樹種,選擇植株頂端向陽位置,將7月1日—7日間展開的葉片作為早生葉進行掛牌標記。將9月1日—7日間展開的葉片作為晚生葉進行掛牌標記。從葉片展開到采樣結(jié)束,早生葉臭氧累計量AOT40約為28.2 μL L-1h,晚生葉臭氧累積量AOT40約為14.2 μL L-1h。

1.3 指標測定

采樣時間為10月10日上午,采樣時植株株高為(80±7) cm,基徑為(11±1) mm,處理間株高,基徑無顯著差異。每個開頂式氣室內(nèi)選擇3株長勢良好的植株,每個植株分別選擇2—3片標記的早生葉和晚生葉進行采樣,取樣時葉片避開葉脈分為兩部分,一部分用保溫箱快速轉(zhuǎn)移到4 ℃冰箱中,于2—3d內(nèi)完成葉綠素a和b、類胡蘿卜素、花青苷和類黃酮的測定,另一部分用液氮罐轉(zhuǎn)移到-80 ℃冰箱內(nèi)用于生長激素測定。

葉綠素的測定取50 mg新鮮葉片,在4℃環(huán)境下剪碎后用4 mL 95% 的乙醇溶液浸泡提取,取提取液用分光光度計(型號)測定664、648、470 nm 波長吸光度,根據(jù)Lichtenthaler[23]的修正公式計算葉綠素a、b總量以及類胡蘿卜素含量。

花青苷和類黃酮相對含量的測定分別參照Pirie[24]和Caldwell[25]的方法并略作改進,取100 mg新鮮葉片,用5mL 0.1% HCl甲醇4 ℃浸泡提取24 h,取提取液用分光光度計(型號)于530 nm(花色素苷)和 300 nm(類黃酮)處測定吸光值。用每g葉片在530 nm處的吸收值OD530/g鮮重表示葉片中花色素苷相對含量,OD300/g鮮重作為葉片中類黃酮相對含量[26]。

脫落酸(ABA)含量的測定酶聯(lián)免疫吸附測定法(ELISA)[27]。

1.4 數(shù)據(jù)分析

臭氧和干旱分別作為影響因子對各指標的作用以及交互作用利用雙因素方差Two-way ANOVA分析進行。處理間多因素比較采用LSD法。所有數(shù)據(jù)在處理前均進行了方差齊性和正態(tài)分布檢驗。數(shù)據(jù)分析采用SPSS 17.0 軟件進行,并利用Sigmaplot 11.0進行繪圖。

2 結(jié)果

2.1 總?cè)~綠素和類胡蘿卜素含量

圖1 臭氧濃度增加和干旱處理對早生葉和晚生葉總?cè)~綠素和類胡蘿卜素含量的影響 Fig.1 The effects of elevated ozone and drought stress on total chlorophyll (Chl (a+b)) and carotenoid (Car) contents in early-flush and late-flush leaves圖中不同字母表示處理間多重比較差異顯著 (P<0.05)

早生葉總?cè)~綠素和類胡蘿卜素含量在臭氧處理后顯著降低,降低百分比分別為21%和29.6%(圖1,表1)。早生葉總?cè)~綠素含量在干旱處理后顯著降低了18.7%。共同處理對早生葉片總?cè)~綠素含量具有顯著交互作用,交互作用表明總?cè)~綠素下降了18.6%,介于單獨臭氧和干旱處理之間(圖1,表1)。晚生葉總?cè)~綠素在干旱處理后顯著降低了18.8%,臭氧單獨或共同處理未對晚生葉上述指標產(chǎn)生顯著影響(圖1,表1)。

2.2 花青苷和類黃酮色素相對含量

早生葉花青苷和類黃酮相對含量在臭氧處理后分別顯著增加了34.1%和7.3%,在干旱處理后分別顯著增加了37%和7.4%。共同處理對早生葉中花青苷相對含量產(chǎn)生了顯著的交互作用,處理后花青苷相對含量升高了34.2%,介于單獨臭氧和干旱處理之間(圖2,表1)。臭氧、干旱以及共同處理未對晚生葉葉片花青苷和類黃酮相對含量產(chǎn)生顯著影響。

圖2 臭氧增加和干旱處理對早生葉和晚生葉花色素苷和類黃酮相對含量的影響Fig.2 The effects of elevated ozone and drought stress on anthocyanin and flavonoid relative contents in early-flush and late-flush leaves圖中不同小寫字母表示處理間多重比較差異顯著 (P<0.05)

因素Factors葉齡Leafage總?cè)~綠素Chlorophyll類胡蘿卜Carotenoid花青苷Anthocyanin類黃酮Flavonoid脫落酸ABA臭氧Ozone早生葉0．02?0．01??0．03?0．02?0．01??晚生葉0．580．620．540．110．95干旱Drought早生葉0．05?0．060．02?0．02?0．01??晚生葉0．04?0．110．520．480．01??臭氧×干旱早生葉0．02?0．190．02?0．250．03?Ozone×Drought晚生葉0．320．330．260．170．96

表中數(shù)值為P值,*P<0.05,**P<0.01,***P<0.001

2.3 脫落酸含量

早生葉脫落酸含量在臭氧和干旱單獨處理后均顯著升高,升高幅度分別為19.8%和13%。共同處理對早生葉脫落酸含量有顯著交互作用,處理后脫落酸含量升高了20.8% (圖3,表1),略高于單獨的臭氧和干旱處理。晚生葉在干旱處理后脫落酸含量顯著上升了33.4%。臭氧和共同處理未對晚生葉葉片脫落酸含量產(chǎn)生顯著影響。

3 討論

圖3 臭氧增加和干旱處理對早生葉 和晚生葉 葉片脫落酸(ABA)含量的影響Fig.3 The effects of elevated ozone and drought stress on abscisic acid (ABA) contents in early-flush and late-flush leaves圖中不同小寫字母表示處理間多重比較差異顯著 (P<0.05)

葉綠素和類胡蘿卜是重要的光合色素也同時影響著葉片的顏色,光合色素含量的下降意味著葉片光合能力的降低。臭氧和干旱脅迫對葉綠素的分解作用已經(jīng)被大量研究證實[5,10,28],本實驗結(jié)果也表明臭氧濃度升高和干旱處理導(dǎo)致早生葉總?cè)~綠素含量下降(圖1)。交互作用表明葉片早生葉總?cè)~綠素含量介于單獨臭氧和干旱處理之間,說明干旱保護和減緩了臭氧對葉片葉綠素的下降作用(圖1,表1)?？赡艿慕忉屖菤饪资浅粞踹M入葉片的主要通道,而干旱能夠降低葉片的氣孔導(dǎo)度[12],從而減少了葉片對臭氧的攝入量[29-30]。

元寶楓是一種具有秋季觀賞價值的彩葉樹種,花青苷和相關(guān)的可溶性糖結(jié)合形成紅色,樹木秋季葉片呈現(xiàn)的鮮紅色便是葉綠素含量減少花青苷的合成增加的結(jié)果[12,31],類黃酮也能在秋季提升葉片的亮度[14]。本實驗結(jié)果表明,臭氧和干旱處理后早生葉葉片花青苷和類黃酮相對含量均顯著增加(圖2,表1),研究表明花青苷作為一種可溶性黃酮類物質(zhì),其含量的增加能夠降低滲透壓減輕干旱脅迫[16,18],增加葉片對臭氧抗氧化性[17]。花青苷交互作用的結(jié)果表明,臭氧的存在緩解了干旱造成的早生葉花青苷含量的上升,目前未發(fā)現(xiàn)臭氧和干旱復(fù)合影響對花青苷影響的研究,所以具體響應(yīng)機制仍不明確。

脫落酸是能夠降低葉片氣孔導(dǎo)度、加速葉片衰老、脫落的主要植物激素[32- 34]。本實驗結(jié)果表明,臭氧和干旱處理均導(dǎo)致葉片脫落酸含量升高,交互作用表現(xiàn)脫落酸含量大于單獨臭氧和干旱處理,變化趨勢與之前發(fā)表的光合測量結(jié)果-氣孔導(dǎo)度在處理后的下降趨勢相符合[10]。對于元寶楓等不敏感樹種,葉片氣孔臭氧、干旱等脅迫的反應(yīng)是ABA含量升高以調(diào)控氣孔關(guān)閉,減少水分散失和臭氧進入,交互作用的結(jié)果也與一些文獻結(jié)果一致[35-36],脫落酸含量升高會導(dǎo)致葉片早衰,提前脫落,變色期變短。

晚生葉和早生葉對臭氧濃度升高和干旱處理的響應(yīng)不同。晚生葉總?cè)~綠素和脫落酸含量對干旱處理較為敏感,這可能與晚生葉蒸騰作用較為強烈有關(guān)。在早生葉中,除了類胡蘿卜素外,臭氧濃度升高和干旱處理均對早生葉相關(guān)指標產(chǎn)生了顯著影響。早生和晚生葉對臭氧處理的響應(yīng)差異可能與以下原因有關(guān)：1)臭氧對葉片的傷害具有明顯的時間累積效應(yīng)[37],受害程度與臭氧累積量正相關(guān),而早生葉接受臭氧熏蒸的時間較長,因此臭氧累積量大于晚生葉。2)晚生葉對臭氧的適應(yīng)性。有研究表明,植物在受到臭氧威脅后植株會產(chǎn)生更多的抗氧化類物質(zhì)如抗壞血酸等輸送到更重要的幼嫩器官如晚生葉片中[38],因此晚生葉抗氧化能力可能強于早生葉,這也可能是晚生葉受臭氧影響較小的原因。在本實驗中,由于未對葉片開始變紅、變紅持續(xù)時間、落葉時間和葉片顏色色度進行監(jiān)測和分析,所以難以詳細評價臭氧和干旱對元寶楓秋季物候變化的影響程度。

4 結(jié)論

(1)元寶楓早生葉和晚生葉對干旱和臭氧的響應(yīng)不同,早生葉對臭氧處理響應(yīng)大于晚生葉,而晚生葉對干旱處理更敏感。

(2)臭氧濃度升高和干旱均加速了葉片衰老。處理后早生葉光合色素減少、花青苷和類黃酮增加、葉片ABA含量增加,這些變化將會改變元寶楓秋季葉片秋季變色時間,影響元寶楓秋季物候和作為彩葉樹的觀賞價值。

(3)共同處理后葉片脫落酸含量增加,葉片提前脫落風(fēng)險增加。

致謝：北京城市生態(tài)站宋文質(zhì)工程師和姚余輝老師在OTC設(shè)計,搭建和運行過程中給予幫助,張紅星老師在設(shè)備安裝中提供幫助,馮兆忠老師幫助寫作，特此致謝。

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The effects of elevated ozone and chronic drought on leaf pigments and abscisic acid contents in early and late-flush leaves of Shantung maple (AcertruncatumBunge)

LI Li1, NIU Junfeng2, WEN Zhi1, CUI Jian3, WANG Xiaoke1,*

1StateKeyLaboratoryofUrbanandRegionalEcology,ResearchCenterforEco-EnvironmentalSciences,ChineseAcademyofSciences,Beijing100085,China2SouthChinaBotanicalGarden,ChineseAcademyofSciences,Guangzhou510650,China3InstituteofAgricultureResourcesandRegionalPlanning,ChineseAcademyofAgricultureSciences,Beijing100081,China

The changing color of leaves in autumn is not only necessary for the growth of foliage trees but is also important for urban landscape interests. Red color in maple leaves relates to the synthesis of anthocyanin and the degraded pigments. Ozone (O3) is an important phytotoxic pollutant, which may affect the basic physiological functions of plants due to its highly reactive oxidative characteristics. The increased consumption of fossil fuels in China has led to increased emission of O3precursors and visible plant injury induced by high O3concentration frequently occurs around Beijing. In addition, trees are often subjected to periodic drought in North China with the frequency and the severity of drought events projected in the background of climate change. Drought in summer usually coincides with episodes of high O3concentrations, which, together, may affect plant growth including color expression and leaf senescence of foliage tree species in fall. Although numerous publications have reported the effects of elevated O3concentration or drought stress on trees, little is known about the possible interactions between anthocyanin and flavonoid in Asian maple species. To investigate the effects of chronic drought stress and elevated O3concentrations on leaf pigments and abscission of Shantung maple (AcertruncatumBunge), we set up 12 open-top chambers with four treatments (AW: non-filtered ambient air and well watered; AW + 60: non-filtered ambient air plus 60 nL/L O3and well watered; AD: non-filtered ambient air and drought; AD + 60: non-filtered ambient air plus 60 nL/L O3and drought) in a suburb of Beijing, China. Total chlorophyll (total Chl), carotenoid (Car), anthocyanin, flavonoid, and abscisic acid (ABA) contents in early and late-flush leaves were measured in October of the first year. Leaves that unfolded from July 1 to 7 were marked as early-flush leaves and the AOT40 (The cumulative O3 exposure, which was described as the accumulated hourly mean O3concentrations over 40 ppb during O3 fumigation period) was 28.2 μL L-1h when harvested. Late-flush leaves unfolded from September 1 to 7 and the AOT40 was 14.2 μL L-1h when harvested. The results showed: (1) For early-flush leaves, elevated O3significantly decreased the total Chl and Car contents by 21% and 29.6%, respectively, increased anthocyanin and flavonoid relative contents by 34.1% and 7.3%, respectively, and increased ABA contents by 19.8%. Drought stress decreased the total Chl by 18.7%, increased the relative contents of anthocyanin and flavonoid by 37% and 7.4%, respectively, and increased ABA contents by 13%. These physiology changes would collectively lead to leaf reddening, senescence, and abscission in advance of autumn. (2) Late-flush leaves only responded to drought treatments as indicated by a significant decrease of 18.8% in total Chl and an increase of 33.4% in ABA contents. (3) Significant interactions were found in total Chl, anthocyanin, and ABA contents of early-flush leaves, as indicated by the fact that the decrease in total Chl and increase in anthocyanin were mitigated, but the increase in ABA contents was aggravated. In conclusion, early and late-flush leaves responded differently to elevated O3and drought stress. Early-flush leaves responded more to ozone treatment, while late-flush leaves were more sensitive to drought stress. Both treatments lead to leaf early senescence and their interactive treatments may increase the risk of early abscission. This study may provide a better understanding of autumnal leaf growth and the phenology response to elevated O3and drought stress in the coming future.

AcertruncatumBunge; ozone; drought; photosynthetic pigment; anthocyanin; flavonoid; ABA

國家自然科學(xué)基金項目(31170424, 41571053, 71533005)

2015- 05- 06;

日期:2016- 03- 03

10.5846/stxb201505060933

*通訊作者Corresponding author.E-mail: wangxk@rcees.ac.cn

李麗, ?？》? 文志, 崔健, 王效科.干旱和臭氧濃度升高對元寶楓早生和晚生葉片色素和脫落酸含量的影響.生態(tài)學(xué)報,2016,36(21):6804- 6811.

Li L, Niu J F, Wen Z, Cui J, Wang X K.The effects of elevated ozone and chronic drought on leaf pigments and abscisic acid contents in early and late-flush leaves of Shantung maple (AcertruncatumBunge).Acta Ecologica Sinica,2016,36(21):6804- 6811.