祁 虹, 段留生, 王樹林, 王 燕, 張 謙, 馮國(guó)藝, 杜海英, 梁青龍, 林永增**

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全生育期UV-B輻射增強(qiáng)對(duì)棉花生長(zhǎng)及光合作用的影響*

祁 虹1, 段留生2, 王樹林1, 王 燕1, 張 謙1, 馮國(guó)藝1, 杜海英1, 梁青龍1, 林永增1**

(1. 河北省農(nóng)林科學(xué)院棉花研究所/農(nóng)業(yè)部黃淮海半干旱區(qū)棉花生物學(xué)與遺傳育種重點(diǎn)實(shí)驗(yàn)室 石家莊 050051; 2. 中國(guó)農(nóng)業(yè)大學(xué)農(nóng)學(xué)院 北京 100083)

植物光合系統(tǒng)是UV-B輻射最初和最重要的作用靶標(biāo)。本文在大田條件下進(jìn)行紫外燈照射處理, 研究全生育期UV-B輻射增強(qiáng)(高于環(huán)境20%和40%)對(duì)棉花形態(tài)、干物質(zhì)積累、光合色素和產(chǎn)量的影響, 并通過分析棉花主莖功能葉片的氣體交換參數(shù)和葉綠素?zé)晒鈪?shù), 探討UV-B輻射增強(qiáng)影響棉花光合作用的機(jī)制。結(jié)果表明, UV-B輻射增強(qiáng)抑制了棉花生長(zhǎng)和干物質(zhì)積累, 籽棉產(chǎn)量顯著降低, 且UV-B輻射越強(qiáng), 抑制作用越明顯。隨UV-B輻射的增強(qiáng), 棉花主莖功能葉的凈光合速率(n)在各生育期均顯著降低, 葉綠素含量呈先升高后降低趨勢(shì), 氣孔導(dǎo)度(s)和蒸騰速率(r)未發(fā)生變化, 胞間CO2濃度(i)反而升高, 說明n下降主要由非氣孔限制因素造成。對(duì)葉綠素?zé)晒鈪?shù)的分析表明, PSⅡ的最大光化學(xué)量子產(chǎn)率(v/m)、實(shí)際光化學(xué)量子效率(PSII)、線性電子傳遞速率(ETR)和光化學(xué)淬滅系數(shù)()隨著UV-B輻射的增強(qiáng)而降低, 非光化學(xué)猝滅系數(shù)(NPQ)則顯著升高, 且各葉綠素?zé)晒鈪?shù)與n變化均顯著相關(guān); 慢速弛豫NPQ(NPQS)及其在NPQ中的比例均隨UV-B輻射的增強(qiáng)而顯著提高, 表明PSⅡ反應(yīng)中心受損, 光化學(xué)效率降低。以上結(jié)果證明, 全生育期UV-B輻射增強(qiáng)降低了棉花的光合葉面積、葉綠素含量和凈光合速率, 引起棉花生長(zhǎng)與物質(zhì)積累受抑, 產(chǎn)量降低。UV-B輻射增強(qiáng)引起的光合速率下降與PSⅡ反應(yīng)中心遭到破壞密切相關(guān)。

UV-B輻射增強(qiáng); 棉花生長(zhǎng); 氣體交換; 光系統(tǒng)Ⅱ(PSⅡ); 葉綠素?zé)晒鈪?shù); 慢速弛豫NPQ

近些年人類活動(dòng)排放的氯氟烴類物質(zhì)(chloro- fluoro-carbon, CFCs)使臭氧層變薄, 導(dǎo)致到達(dá)地表的紫外線(主要是波長(zhǎng)為280~320 nm的B區(qū), 簡(jiǎn)稱UV-B輻射)不斷增強(qiáng)[1-2]。目前南半球的UV-B輻射強(qiáng)度較1979—1992年水平提高40%, 而北半球則提高14%[3]。由于氯氟烴類化合物半衰期長(zhǎng)達(dá)50~150年[4], 地球上的生物還將長(zhǎng)期遭受UV-B輻射增強(qiáng)的影響。

UV-B輻射增強(qiáng)對(duì)植物以及整個(gè)生態(tài)系統(tǒng)的影響已經(jīng)成為各國(guó)科學(xué)家關(guān)注的焦點(diǎn)。前人研究表明, UV-B輻射可以攻擊植物的DNA[5]、蛋白質(zhì)[6]和膜系統(tǒng)[7], 從而對(duì)植物的生長(zhǎng)發(fā)育、生理代謝等多方面產(chǎn)生負(fù)面影響[8]。在植物的各種生理過程中, 光合系統(tǒng)是UV-B輻射最初和最重要的作用靶標(biāo)[9]。UV-B輻射增強(qiáng)條件下, 油菜(L.)[10]、高粱[(L.) Moench][11]、丹參(Bge.)[12]、水稻(L.)[13]、玉米(L.)[14]等作物的光合作用均受到了不同程度的抑制。光合作用的下降可能與光合色素含量減少[7]、光合酶活性受抑[15]以及光系統(tǒng)Ⅱ(photosystem Ⅱ complex, PSⅡ)效率降低[16]等有關(guān)。然而, 這些結(jié)果絕大多數(shù)是從培養(yǎng)箱或溫室試驗(yàn)中得到的。Booij-James等[17]研究發(fā)現(xiàn), 在光合有效輻射(photosynthetic active radiation, PAR)為50~200 μmol·m–2·s–1條件下, UV-B輻射只增加1.24 μmol·m–2·s–1, 擬南芥[(L.) Heynh.]PSⅡ中的D1和D2蛋白也會(huì)大量降解; 而當(dāng)PAR上升到450~500 μmol·m–2·s–1時(shí), 即使UV-B輻射提高32~40 kJ·m–2·d–1, 豌豆(L.)PSⅡ的最大光化學(xué)效率(v/m)與PSⅡ的實(shí)際光化學(xué)效率(PSⅡ)也沒有發(fā)生顯著變化[18]。這表明UV-B輻射對(duì)植物的傷害很大程度上取決于PAR的強(qiáng)度。而在培養(yǎng)箱或溫室條件下, PAR遠(yuǎn)低于大田環(huán)境, UV-B輻射增強(qiáng)對(duì)植物和光合系統(tǒng)的傷害很容易被高估[19-20]。因此, 在大田條件下研究全生育期UV-B輻射增強(qiáng)對(duì)作物光合系統(tǒng)和生長(zhǎng)的影響具有重要的理論和現(xiàn)實(shí)意義。

棉花(L.)是重要的經(jīng)濟(jì)作物, 對(duì)UV-B輻射增強(qiáng)非常敏感。在溫室與大田條件下增強(qiáng)UV-B輻射, 棉花均表現(xiàn)出株高變矮, 葉面積減小, 干物重下降[21-22], 葉綠素含量與光合速率降低[23-24], 產(chǎn)量與品質(zhì)也顯著下降[25]。但有關(guān)UV-B輻射增強(qiáng)影響棉花光合作用的機(jī)制尚鮮見報(bào)道。本文以棉花作為受試材料, 在大田條件下, 研究了全生育期UV-B輻射增強(qiáng)對(duì)棉花生長(zhǎng)、物質(zhì)生產(chǎn)、光合色素含量和產(chǎn)量的影響, 并通過分析棉花葉片的氣體交換參數(shù)和葉綠素?zé)晒鈪?shù)變化探討UV-B輻射增強(qiáng)影響棉花光合作用的機(jī)制。

1 材料與方法

1.1 試驗(yàn)設(shè)計(jì)

供試棉花材料選用轉(zhuǎn)基因抗蟲棉品種‘中棉所41’。試驗(yàn)為3年, 2012—2013年測(cè)定生長(zhǎng)、發(fā)育等形態(tài)學(xué)指標(biāo), 2013年測(cè)定葉片氣體交換參數(shù)和葉綠素?zé)晒鈪?shù), 2014年測(cè)定熒光暗弛豫動(dòng)力學(xué)。試驗(yàn)采取大田種植, 安排在河北省邢臺(tái)市威縣棗園鄉(xiāng)東張莊村(36o56￠N, 115o26￠E)。試驗(yàn)田連續(xù)多年植棉, 一熟棉田, 土壤中等地力, 含有機(jī)質(zhì)8.53 g·kg–1, 全氮0.578 g·kg–1, 有效磷40.3 mg·kg–1, 速效鉀124 mg·kg–1。

試驗(yàn)設(shè)置3個(gè)處理: U0, 對(duì)照, 環(huán)境UV-B輻射強(qiáng)度; U1, 設(shè)計(jì)高于環(huán)境UV-B輻射強(qiáng)度20%; U2, 設(shè)計(jì)高于環(huán)境UV-B輻射強(qiáng)度40%。每行棉花上方懸掛1排紫外燈管(長(zhǎng)1.2 m, 中心波長(zhǎng)297 nm, 40 W), 用醋酸纖維素膜包裹以濾掉280 nm以下波段, 通過調(diào)整燈管高度控制到達(dá)棉花頂部的紫外輻射強(qiáng)度。分別于2012年5月中旬、6月中旬、7月中旬和8月中旬的晴天, 從8:00至18:00, 每隔15 min測(cè)定1次棉花冠層環(huán)境UV-B輻射強(qiáng)度, 以時(shí)間為橫坐標(biāo), UV-B輻射強(qiáng)度為縱坐標(biāo)繪制曲線并模擬方程, 以拋物線與軸的環(huán)繞面積作為試驗(yàn)地的環(huán)境UV-B輻射強(qiáng)度(kJ·m–2·d–1), 每月根據(jù)環(huán)境UV-B輻射強(qiáng)度變化調(diào)整各處理的輻射劑量, 2013年和2014年的UV-B處理強(qiáng)度參照2012年的環(huán)境強(qiáng)度設(shè)定, 實(shí)際處理強(qiáng)度如表1所示。環(huán)境及各處理UV-B輻射強(qiáng)度使用紫外輻射計(jì)(環(huán)地牌, 北京師范大學(xué)光電儀器廠)測(cè)定297 nm處強(qiáng)度。UV-B輻射增強(qiáng)處理從棉花三葉期開始, 至吐絮期結(jié)束, 每天照射10 h (8:00—18:00), 陰天或下雨關(guān)閉紫外燈。每個(gè)處理設(shè)置4個(gè)重復(fù), 采取完全隨機(jī)設(shè)計(jì)排列, 每個(gè)重復(fù)棉花4行, 長(zhǎng)度3.6 m, 小區(qū)面積10.8 m2。試驗(yàn)采用覆膜直播, 大小行種植, 大行行距105 cm, 小行行距45 cm, 株距22 cm, 密度6.0萬株·hm–2。

表1 不同棉花生育期各處理的UV-B輻射強(qiáng)度

1.2 測(cè)定方法

1.2.1 生長(zhǎng)、干物質(zhì)積累和產(chǎn)量

分別于2012年和2013年的6月5日、6月25日、7月15日、8月5日和8月25日, 調(diào)查各處理棉花的株高、節(jié)數(shù)和子葉節(jié)莖粗, 各小區(qū)分別連續(xù)調(diào)查20株, 取算術(shù)平均數(shù); 同時(shí)隨機(jī)取棉株3棵, 室內(nèi)測(cè)定其果枝總長(zhǎng)和葉片數(shù), 用SHY-150掃描式活體面積測(cè)量?jī)x測(cè)定棉花單株總?cè)~面積, 計(jì)算葉面積指數(shù)(LAI)[26]:

LAI=單株棉花葉片總面積/

單株棉花所占土地面積 (1)

將棉株分解, 地上部與根系分別烘干稱重。計(jì)算棉花的相對(duì)生長(zhǎng)速率(PGR)[27]:

PGR=(ln2–ln1)/(2–1) (2)

式中:1和2分別為時(shí)間1和2時(shí)的單株棉花干重。

9月10日每小區(qū)連續(xù)調(diào)查20株棉花成鈴數(shù), 取平均數(shù)作為單株成鈴數(shù); 收獲中部吐絮棉鈴, 計(jì)算單鈴重。

籽棉產(chǎn)量=單株鈴數(shù)×密度×單鈴重×0.85 (3)

1.2.2 氣體交換參數(shù)及葉片葉綠素?zé)晒鈪?shù)測(cè)定

棉花葉片氣體交換參數(shù)和葉綠素?zé)晒庀嚓P(guān)參數(shù)采用Li-6400便攜式光合儀測(cè)定。分別于2013年的棉花蕾期(6月24日)、盛花期(7月15日)、盛鈴期(8月8日)和吐絮期(8月27日), 選擇晴天上午9:00—11:00測(cè)定棉花主莖倒三葉的凈光合速率(n)、蒸騰速率(r)、氣孔導(dǎo)度(s)和胞間CO2濃度(i), 采用開放式氣路, 光源由LED紅藍(lán)光源提供, 光強(qiáng)設(shè)定為1 400 μmol·m–2·s–1, 氣體流量500 μmol·s–1。在黎明前測(cè)定棉花主莖倒三葉的PSⅡ初始熒光(o)、最大熒光(m); 在光適應(yīng)狀態(tài)下測(cè)定光下初始熒光(o￠)、光下最大熒光(m￠)和穩(wěn)態(tài)熒光(s)。計(jì)算以下PSⅡ相關(guān)參數(shù):

最大量子產(chǎn)量(v/m)=(m–o)/m(4)

光化學(xué)量子效率(PSⅡ)=(m￠–s)/m￠(5)

線性電子傳遞速率(ETR)=PPFD×PSⅡ×0.84×0.5 (6)

光化學(xué)猝滅系數(shù)()=(m￠–s)/(m￠–o￠) (7)

非光化學(xué)猝滅系數(shù)(NPQ)=(m–m￠)/m￠(8)

高等植物NPQ可以分為兩部分: 高能態(tài)猝滅(hight energy state quenching,)和光抑制猝滅(photoinhibitory quenching,)[28]。棉花葉片的NPQ組成采用熒光暗弛豫動(dòng)力學(xué)進(jìn)行分析, 參照Griffiths和Maxwell的方法[29], 有所改動(dòng)。將NPQ分解為兩部分, 快速弛豫NPQ(rapidly relaxing NPQ, NPQF), 代表; 緩慢弛豫NPQ(slowly relaxing NPQ, NPQS), 代表。將充分光適應(yīng)的棉花主莖倒三葉放入Li-6400便攜式光合儀熒光葉室, 在黑暗條件下每隔5 min打一次飽和光(1 500 μmol·m–2·s–1), 同時(shí)測(cè)量其最大熒光值, 連續(xù)測(cè)量1 h。NPQF計(jì)算公式如下:

NPQF=(m–mr)/mr(9)

NPQS=NPQ–NPQF(10)

式中:mr為弛豫平衡后的最大熒光值。

1.2.3 光合色素含量測(cè)定

參照Cambrollé[30]的方法, 在測(cè)定完氣體交換參數(shù)后, 取同一葉片, 去葉脈稱取0.5 g, 加入10 mL 80% 的丙酮溶液, 充分浸提后過濾, 取上清1 mL, 再加入2 mL丙酮溶液, 在663 nm和646 nm下測(cè)定溶液吸光值, 按照Lichtenthaler的方法[31]計(jì)算葉綠素a (Chla)、葉綠素b (Chlb)和總?cè)~綠素(Chla+b)的含量。

1.3 統(tǒng)計(jì)分析

所有數(shù)據(jù)用DPS 7.55軟件進(jìn)行統(tǒng)計(jì)分析。

2 結(jié)果與分析

2.1 不同程度UV-B輻射增強(qiáng)對(duì)棉花生長(zhǎng)的影響

如表2所示, 兩年的試驗(yàn)結(jié)果趨勢(shì)一致, 棉花各生育期的株高、果枝總長(zhǎng)以及子葉節(jié)莖粗均隨著UV-B輻射的增強(qiáng)呈下降趨勢(shì), 表明UV-B輻射增強(qiáng)對(duì)棉花莖干的縱向伸長(zhǎng)和橫向增粗均有抑制作用; 但除苗期的U2處理外, 各處理不同生育期節(jié)數(shù)均未發(fā)生顯著變化, 說明UV-B輻射增強(qiáng)對(duì)莖干伸長(zhǎng)的抑制作用主要是由于節(jié)間變短造成的。棉花的葉片生長(zhǎng)受到UV-B輻射增強(qiáng)的抑制, LAI在不同年份均隨UV-B輻射的增強(qiáng)而顯著降低。從抑制程度看, 棉花苗期對(duì)UV-B輻射更為敏感, U2處理下棉花LAI在2012年和2013年的苗期(6月5日)分別比U0降低56.6%和48.3%, 而在吐絮期(8月25日)則分別降低39.4%和30.3%。

2.2 不同程度UV-B輻射增強(qiáng)對(duì)棉花干物質(zhì)積累和產(chǎn)量的影響

兩年的干物質(zhì)積累和分配結(jié)果如表3所示。隨著UV-B輻射的增強(qiáng), 棉花地上部與根系干物質(zhì)量均顯著減少, 根冠比則有所提高, 表明UV-B輻射增強(qiáng)對(duì)棉花地上部的抑制作用大于根系。相對(duì)生長(zhǎng)速率(PGR)表示植株的生長(zhǎng)能力。由表3看出, 各處理下棉花的PGR均隨著生育期的推進(jìn)逐漸降低, 在棉花生育前期, PGR顯著受到UV-B增強(qiáng)的抑制, 但在進(jìn)入花鈴期以后(8月5日)反而隨UV-B的增強(qiáng)而提高。這可能是由于UV-B增強(qiáng)條件下棉株結(jié)鈴少后期營(yíng)養(yǎng)生長(zhǎng)旺盛造成的。3年的棉花籽棉產(chǎn)量結(jié)果表現(xiàn)一致, 均隨著UV-B輻射的增強(qiáng)而顯著降低。從產(chǎn)量構(gòu)成因素看, 單鈴重與單株鈴數(shù)均有隨UV-B輻射增強(qiáng)而降低的趨勢(shì)(表4)。

2.3 不同程度UV-B輻射增強(qiáng)對(duì)棉花氣體交換參數(shù)的影響

如圖1所示, 在各生育期, 棉花主莖功能葉的n隨UV-B輻射的增強(qiáng)而顯著降低, 但s和r未發(fā)生顯著變化,i則與n變化相反, 隨UV-B輻射的增強(qiáng)有升高趨勢(shì)。UV-B輻射增強(qiáng)對(duì)n的抑制在生育前高于中后期, 蕾期(6月24日)U1和U2處理棉花n分別比對(duì)照降低15.0%和56.4%, 到初花期(7月15日)則分別降低9.0%和22.9%。

2.4 不同程度UV-B輻射增強(qiáng)對(duì)棉花葉片光合色素含量與組成的影響

葉綠素是植物進(jìn)行光合作用的主要色素。U1處理下, 棉花主莖功能葉中Chla和Chlb含量均略有升高, Chla/Chlb值沒有顯著差異; 而U2處理下Chla和Chlb含量顯著下降, Chla/Chlb比值顯著降低(表5)。

2.5 不同程度UV-B輻射增強(qiáng)對(duì)棉花主莖功能葉葉綠素?zé)晒鈪?shù)的影響

葉綠素?zé)晒馐枪夂献饔玫奶结? 通過對(duì)熒光參數(shù)的測(cè)定和分析, 可以了解植物光合作用響應(yīng)環(huán)境的變化及影響機(jī)制[32]。各處理下棉花主莖功能葉的葉綠素?zé)晒鈪?shù)結(jié)果顯示(圖2),v/m、PSⅡ、ETR和均隨UV-B輻射的增強(qiáng)而降低, 而NPQ則顯著升高。從變化幅度來看, 各處理的葉綠素?zé)晒鈪?shù)均隨著UV-B輻射處理時(shí)間的延長(zhǎng), 差異逐漸減小, 以PSⅡ?yàn)槔? 蕾期(6月24日)U1和U2處理分別比對(duì)照降低24.1%和29.5%, 盛花期(7月15日)降低3.4%和12.9%, 而到盛鈴期(8月8日)U1處理與對(duì)照已無顯著差別, U2也只降低了6.2%。這一結(jié)果表明棉花生育前期對(duì)UV-B輻射增強(qiáng)更為敏感。

表2 不同程度UV-B輻射增強(qiáng)對(duì)不同生育期棉花生長(zhǎng)的影響

同一年份數(shù)字標(biāo)注不同字母表示差異顯著(<0.05)。The data with different letters in the same year are significantly different (< 0.05).

表3 不同程度UV-B輻射增強(qiáng)對(duì)棉花干物質(zhì)積累和分配的影響

地上部干重為棉花莖、葉和蕾鈴的干物重之和。同一年份數(shù)字標(biāo)注不同字母表示差異顯著(<0.05)。Dry matter of the aboveground part is the total dry weight of stems, leaves, buds and bolls. The data with different letters in the same year are significantly different (< 0.05).

同一年份數(shù)字標(biāo)注不同字母表示差異顯著(<0.05)。The data with different letters in the same year are significantly different (< 0.05).

n: 凈光合速率;s: 氣孔導(dǎo)度;i: 胞間CO2濃度;r: 蒸騰速率。n: net photosynthetic rate;s: stomatal conductance;i: intercellular CO2concentration;r: transpiration rate.

植物葉片的暗弛豫動(dòng)力學(xué)測(cè)定可以分析NPQ變化的機(jī)制。根據(jù)凈光合速率和葉綠素?zé)晒鈪?shù)的測(cè)定結(jié)果, 選取棉花對(duì)UV-B輻射增強(qiáng)最為敏感的蕾期(6月24日), 對(duì)不同UV-B輻射處理下主莖功能葉片進(jìn)行了暗弛豫動(dòng)力學(xué)分析, 結(jié)果如表6所示。UV-B增強(qiáng)條件下, 棉花主莖功能葉NPQF顯著增大, 但U1處理高于U2處理; 而NPQS則隨UV-B的增強(qiáng)而大幅提高, U1和U2處理分別比對(duì)照提高2.48倍和8.87倍。從組成比例看, NPQF占NPQ的比例隨著UV-B輻射的增強(qiáng)而降低, NPQS的比例則隨著UV-B輻射的增強(qiáng)而顯著提高。

2.6 不同UV-B輻射強(qiáng)度下棉花葉片光合特征參數(shù)的相關(guān)性分析

不同UV-B輻射強(qiáng)度下, 棉花葉片的氣體交換參數(shù)與葉綠素含量、葉綠素?zé)晒鈪?shù)的相關(guān)關(guān)系如表7所示。n與相關(guān)系數(shù)最高, 達(dá)0.901, 與其他葉綠素?zé)晒鈪?shù)的相關(guān)系數(shù)也達(dá)0.83以上, 且均達(dá)0.01顯著水平; 其次是Chla+b, 與n相關(guān)系數(shù)為0.708, 達(dá)0.05顯著水平;n與其他氣體交換參數(shù)(s、i和r)間無顯著相關(guān)性。

表5 不同程度UV-B輻射增強(qiáng)對(duì)棉花葉片葉綠素含量及組成的影響

不同字母表示差異顯著(<0.05)。The data with different letters are significantly different (< 0.05).

表6 不同UV-B輻射強(qiáng)度下棉花葉片NPQ組成分析

NPQ: 非光化學(xué)淬滅系數(shù); NPQF: 快速弛豫NPQ; NPQS: 緩慢弛豫NPQ。不同字母表示差異顯著(<0.05)。NPQ: non-photochemical quenching; NPQF: rapidly relaxing NPQ; NPQS: slowly relaxing NPQ. The data with different letters are significantly different (< 0.05).

表7 不同UV-B輻射強(qiáng)度下棉花葉片光合特征參數(shù)的相關(guān)性分析

n: 凈光合速率;s: 氣孔導(dǎo)度;i: 胞間CO2濃度;r: 蒸騰速率。v/m: PSⅡ的最大光化學(xué)量子產(chǎn)率;PSⅡ: PSⅡ的實(shí)際光化學(xué)量子效率;: 光化學(xué)淬滅系數(shù); ETR: 線性電子傳遞速率; NPQ: 非光化學(xué)淬滅系數(shù)。*: 相關(guān)性達(dá)0.05顯著水平; **: 相關(guān)性達(dá)0.01顯著水平。n: net photosynthetic rate;s: stomatal conductance;i: intercellular CO2concentration;r: transpiration rate;v/m: maximum quantum efficiency of PSⅡ photochemistry;PSⅡ: PSⅡ operating efficiency;: photochemical quenching; ETR: linear electron transport rate; NPQ: non-photochemical quenching. *: correlation significant at 0.05 level; **: correlation significant at 0.01 level.

v/m: PSⅡ的最大光化學(xué)量子產(chǎn)率, 反映PSⅡ的潛在量子效率;PSⅡ: PSⅡ的實(shí)際光化學(xué)量子效率, 反映被用于光化學(xué)途徑激發(fā)能占進(jìn)入PSⅡ總激發(fā)能的比例;: 光化學(xué)淬滅系數(shù), 反映PSⅡ反應(yīng)中心的開放程度; ETR: 線性電子傳遞速率, 代表了植物葉片的總光合速率; NPQ: 非光化學(xué)淬滅系數(shù), 反映了植物熱耗散的能力。v/m: maximum quantum efficiency of PSⅡ photochemistry, reflecting the intrinsic efficiency of PSⅡ;PSⅡ: PSⅡ operating efficiency, reflecting the proportion of absorbed light that is actually used in PSⅡ photochemistry;: photochemical quenching, reflecting the open proportion of PSⅡ reaction center; ETR: linear electron transport rate, an indicator of overall photosynthesis of plant leaf; NPQ: non-photochemical quenching, reflecting the rate of heat loss from PSⅡ.

3 討論

3.1 UV-B輻射增強(qiáng)抑制棉花生長(zhǎng)

UV-B輻射增強(qiáng)是全球環(huán)境變化的重要問題之一, 對(duì)植物的形態(tài)、生長(zhǎng)發(fā)育、生理代謝、干物質(zhì)積累和產(chǎn)量[33-35]等產(chǎn)生多方面的影響。本研究結(jié)果表明, UV-B輻射增強(qiáng)抑制了棉花莖稈的伸長(zhǎng)和增粗, LAI顯著減小, 生長(zhǎng)減緩, 這與在丹參[12]、擬南芥[7]、向日葵(L.)[36]、小麥(L.)[37]、豌豆[38]等作物上的研究結(jié)果一致。葉片是作物進(jìn)行光合作用的主要器官, 葉面積與作物的生物量間存在顯著正相關(guān)關(guān)系[4]。UV-B輻射增強(qiáng)引起的葉面積減少, 必然影響棉花的干物質(zhì)積累與產(chǎn)量形成。

3.2 UV-B輻射增強(qiáng)導(dǎo)致棉花葉片凈光合速率下降, 葉綠素含量降低

光合作用為綠色植物提供物質(zhì)和能量, 是植物生長(zhǎng)發(fā)育的基礎(chǔ)。葉片光合速率的高低是決定作物物質(zhì)生產(chǎn)能力的主要因素之一。本研究表明, 棉花主莖功能葉的n隨UV-B輻射的增強(qiáng)而減小,s未發(fā)生顯著變化,i反而升高, 表明n的降低并非由氣孔開度變化造成。Jansen等[39]研究發(fā)現(xiàn), UV-B輻射增強(qiáng)并不會(huì)引起氣孔的打開或閉合, 而是造成保衛(wèi)細(xì)胞喪失開合的調(diào)節(jié)能力。因此, UV-B輻射增強(qiáng)所引起的n下降, 與氣孔開度無關(guān), 而主要由非氣孔限制因素造成[40-41]。本研究中不同UV-B輻射強(qiáng)度下棉花葉片的n與s和i間無顯著相關(guān)性也驗(yàn)證了這一結(jié)論。

葉綠素是光合有效輻射的主要吸收色素, 其含量與組成對(duì)植物的光合作用與同化機(jī)能產(chǎn)生重要影響[42]。但葉綠素對(duì)UV-B輻射極為敏感, 葉綠體類囊體膜與垛疊結(jié)構(gòu)極易受到UV-B輻射增強(qiáng)的破壞[43]。本研究中, 在UV-B輻射增強(qiáng)40%的條件下, Chla與Chlb含量以及Chla/Chlb均顯著下降。葉綠素含量的減少直接降低葉片對(duì)光能的吸收效率和傳遞速率, 干擾光能在PSⅡ與PSⅠ間的分配和轉(zhuǎn)換, 抑制物質(zhì)合成[44]。Chla/Chlb反映了葉綠體類囊體膜的穩(wěn)定性[45], Chla/Chlb越小, 類囊體膜垛疊越松散, 光化學(xué)活性也越低[46]。UV-B輻射增強(qiáng)條件下Chla/Chlb比值降低, 表明葉綠體結(jié)構(gòu)的穩(wěn)定性和光合磷酸化活性下降, 光合作用受到不利影響。

3.3 UV-B輻射增強(qiáng)導(dǎo)致的光合速率下降與PSⅡ反應(yīng)中心受損密切相關(guān)

在影響植物光合作用的諸多非氣孔限制因素中, PSⅡ的光化學(xué)活性最易受到UV-B輻射的干擾[8]。本研究證明, 不同UV-B輻射強(qiáng)度下,n變化與葉綠素?zé)晒鈪?shù)間存在極顯著相關(guān)關(guān)系,n的高低與PSⅡ的光化學(xué)活性密切相關(guān)。PSⅡ的狀態(tài)與活性能夠通過分析葉綠素?zé)晒庹T導(dǎo)動(dòng)力學(xué)參數(shù)獲得, 反映植物對(duì)光能的吸收、傳遞、耗散與分配, 揭示光合速率變化的內(nèi)在機(jī)制[47]。v/m代表PSⅡ原初光能轉(zhuǎn)換效率[48], 一般穩(wěn)定在0.83左右[49]。UV-B輻射增強(qiáng)條件下, 棉花葉片v/m降低, 表明PSⅡ活性受到脅迫影響發(fā)生抑制, 且UV-B輻射增強(qiáng)越多, 抑制程度越高。同時(shí),PSⅡ、ETR和均隨UV-B輻射強(qiáng)度的增加而減小, 表明PSⅡ的光能轉(zhuǎn)換效率減小, 類囊體膜上電子傳遞鏈的傳遞速率減慢, 反應(yīng)中心逐漸關(guān)閉, PSⅡ光化學(xué)活性降低。

植物在逆境環(huán)境下會(huì)發(fā)生光抑制現(xiàn)象, 產(chǎn)生的過剩光能會(huì)以熱耗散的形式猝滅, 以保護(hù)光合元件免受逆境脅迫的損傷。NPQ與PSⅡ的熱耗散呈線性正相關(guān)[50]。本研究中, 棉花葉片NPQ隨UV-B輻射的增強(qiáng)而增大, 表明UV-B輻射增強(qiáng)條件下過剩的光能不斷增加, 用于光合作用的激發(fā)能比例降低。一般認(rèn)為, 高等植物NPQ可以分為兩部分: 高能態(tài)猝滅(hight energy state quenching,)和光抑制猝滅(photoinhibitory quenching,)[28]。前者與黃素循環(huán)的能量耗散有關(guān), 是植物響應(yīng)脅迫的一種光保護(hù)機(jī)制[51], 可用暗弛豫動(dòng)力學(xué)中的NPQF表示; 后者與PSⅡ反應(yīng)中心D1蛋白的受損情況有關(guān), 可用NPQS表示。本研究結(jié)果顯示, U1處理下NPQF與NPQS均升高, NPQF為NPQ的主要組分; 而在U2處理下NPQS較U1處理顯著提高, 成為NPQ升高的主要因素。這表明, 小幅提高UV-B輻射, 棉花主要依靠主動(dòng)的高能態(tài)猝滅來消耗過剩光能, 以保護(hù)棉花的光合器官免受損傷; 而在大幅提高UV-B輻射條件下, 棉花高能態(tài)猝滅能力下降, PSⅡ反應(yīng)中心遭到破壞成為引起葉片光抑制的主要原因。

3.4 UV-B增強(qiáng)的生物學(xué)效應(yīng)受試驗(yàn)條件和棉花生育時(shí)期的影響

不同培養(yǎng)條件下, UV-B增強(qiáng)對(duì)棉花的影響結(jié)果存在差異。侍福梅等[52]在培養(yǎng)箱中對(duì)棉花幼苗進(jìn)行UV-B輻射處理, 僅在0.32 kJ·m–2·h–1的UV-B輻射強(qiáng)度下照射1.5 h, 棉花葉片萎蔫嚴(yán)重, 葉片細(xì)胞死亡, 而本研究U2處理下(在1.53~2.24 kJ·m–2·h–1UV-B強(qiáng)度下每天連續(xù)照射8 h)棉花葉片仍能進(jìn)行光合作用, 說明溫室低PAR條件使植株對(duì)UV-B輻射更為敏感。本研究還發(fā)現(xiàn), 棉花的莖、葉生長(zhǎng), 葉片凈光合速率以及葉綠素?zé)晒鈪?shù)均表現(xiàn)出前期抑制程度大于后期, 表明棉花不同生長(zhǎng)階段對(duì)UV-B輻射的響應(yīng)存在差異, 幼苗對(duì)UV-B輻射增強(qiáng)更為敏感。

4 結(jié)論

綜上所述, 在大田條件下, 全生育期UV-B輻射增強(qiáng)會(huì)對(duì)棉花生長(zhǎng)、干物質(zhì)積累、光合作用、PSⅡ反應(yīng)中心光化學(xué)效率以及產(chǎn)量形成產(chǎn)生抑制作用, UV-B輻射強(qiáng)度越高, 抑制程度越大; 葉綠素含量則表現(xiàn)為隨著UV-B輻射的增強(qiáng)先升高后降低。UV-B輻射增強(qiáng)引起的光合速率下降主要由非氣孔限制因素造成, 與PSⅡ反應(yīng)中心遭到破壞所導(dǎo)致的光化學(xué)活性下降有關(guān)。

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Effect of enhanced UV-B radiation on cotton growth and photosynthesis*

QI Hong1, DUAN Liusheng2, WANG Shulin1, WANG Yan1, ZHANG Qian1, FENG Guoyi1, DU Haiying1, LIANG Qinglong1, LIN Yongzeng1**

(1. Institute of Cotton Research, Hebei Academy of Agriculture and Forestry Sciences / Key Laboratory of Biology and Genetic Improvement of Cotton in Huanghuaihai Semiarid Area, Ministry of Agriculture, Shijiazhuang 050051, China; 2. College of Agronomy and Biotechnology, China Agricultural University, Beijing 100083, China)

It has been shown that the thinning of ozone layer continuously enhances ambient ultraviolet-B (UV-B) radiation. Enhanced UV-B radiation influences the growth, development and metabolism of crops, of which photosystem is the initial and most important target. In this study, UV-B radiation was increased by 20% and 40% by using ultraviolet lamp during the whole growth period of cotton under field condition, and its effect on cotton morphology, dry matter accumulation, photosynthetic pigment content and seed cotton yield were analyzed. The influencing mechanism of enhanced UV-B radiation on photosynthesis was also investigated by determining gas exchange parameters and chlorophyll fluorescence parameters in functional leaves. The results showed that the growth of cotton stems, leaves and dry matter accumulation were significantly inhibited by enhanced UV-B radiation. The inhibition effects of enhanced UV-B radiation on cotton were more obvious at seedling stage than that at later growth stages. Seed cotton yield also remarkably decreased with increasing UV-B radiation. The contents ofchlorophyll a (Chla) and chlorophyll b (Chlb) increased under the treatment of 20% above ambient UV-B radiation and there was no change in Chla/Chlb. When UV-B radiation increased to 40% above ambient UV-B radiation, Chla, Chlband Chla/Chlbsignificantly decreased. With increasing UV-B radiation, net photosynthetic rate (n) of functional leaves on cotton main stem significantly decreased. Although there were no change in stomatal conductance (s) and transpiration rate (r) under 40% increase in UV-B radiation, while intercellular CO2concentration (i) increased, which indicated that the decline in photosynthesis was mainly caused by non-stomatal limitation factors. The results of chlorophyll fluorescence parameters analysis showed that with increasing UV-B radiation, maximum quantum efficiency (v/m), operating efficiency (PSⅡ), linear electron transport rate (ETR) and photochemical quenching () of PSIIremarkably decreased, but non-photochemical quenching (NPQ)increased. All the chlorophyll fluorescence parameters were significantly correlated withnchanges. Slowly relaxing NPQ (NPQS) and its proportion in NPQ significantly increased under enhanced UV-B radiation, which indicated that the photochemical efficiency of PSⅡ decreased as itsreaction center wasdamaged by elevated UV-B radiation. The results demonstrated that photosynthetic leaf area, chlorophyll content and photosynthetic rate of cotton dropped under enhanced UV-B radiation during the cotton growth period. This inhibited cotton growth, material accumulation and seed cotton yield. Decrease inndue to enhanced UV-B radiation was closely related with the destruction of PSⅡ reaction center.

Enhanced UV-B radiation; Cotton growth; Gas exchange; Photosystem Ⅱ(PSⅡ); Chlorophyll fluorescence parameters; Lowly relaxing NPQ

S562

A

1671-3990(2017)05-0708-12

10.13930/j.cnki.cjea.160801

* 國(guó)家自然科學(xué)基金項(xiàng)目(31171491)和現(xiàn)代農(nóng)業(yè)產(chǎn)業(yè)技術(shù)體系建設(shè)專項(xiàng)資金(CARS-18-21)資助

**通訊作者:林永增, 主要從事棉花栽培與生理生態(tài)研究。E-mail: zaipei@sohu.com

祁虹, 主要從事棉花栽培生理研究。E-mail: qihong83@126.com

2016-09-07

2017-01-19

* This work was supported by the National Natural Science Foundation of China (31171491) and the Special Fund for the Industrail Technology System Construction of Modem Agriculture (CARS-18-21).

** Corresponding author, E-mail: zaipei@sohu.com

Sep. 7, 2016; accepted Jan. 19, 2017

祁虹, 段留生, 王樹林, 王燕, 張謙, 馮國(guó)藝, 杜海英, 梁青龍, 林永增. 全生育期UV-B輻射增強(qiáng)對(duì)棉花生長(zhǎng)及光合作用的影響[J]. 中國(guó)生態(tài)農(nóng)業(yè)學(xué)報(bào), 2017, 25(5): 708-719

Qi H, Duan L S, Wang S L, Wang Y, Zhang Q, Feng G Y, Du H Y, Liang Q L, Lin Y Z. Effect of enhanced UV-B radiation on cotton growth and photosynthesis[J]. Chinese Journal of Eco-Agriculture, 2017, 25(5): 708-719